Hsp90 761123 225376867 2008-07-13T10:39:35Z Boghog2 2428506 /* Isoforms */ reordered gene and protein columns in table; removed unnecessary bolding; centering {{Pfam_box | Symbol = Hsp90 NTD | Name = Hsp90, N-terminal domain | image = hsp90.jpg | width = 270px | caption = Solid ribbon model of the [[yeast]] Hsp90-dimer in complex with ATP (based on {{PDB|2CG9}}). | Pfam= PF02518 | InterPro= IPR003594 | SMART= | PROSITE = PDOC00270 | SCOP = d.122.1.1 | SCOP = 1AH6 | TCDB = | PDB = {{PDB2|1A4H}}, {{PDB2|1AH6}}, {{PDB2|1AH8}}, {{PDB2|1AM1}}, {{PDB2|1AMW}}, {{PDB2|1BGQ}}, {{PDB2|1BYQ}}, {{PDB2|1OSF}}, {{PDB2|1QY5}}, {{PDB2|1QY8}}, {{PDB2|1QYE}}, {{PDB2|1TBW}}, {{PDB2|1TC0}}, {{PDB2|1U0Y}}, {{PDB2|1U2O}}, {{PDB2|1US7}}, {{PDB2|1UY6}}, {{PDB2|1UY7}}, {{PDB2|1UY8}}, {{PDB2|1UY9}}, {{PDB2|1UYC}}, {{PDB2|1UYD}}, {{PDB2|1UYE}}, {{PDB2|1UYF}}, {{PDB2|1UYG}}, {{PDB2|1UYH}}, {{PDB2|1UYI}}, {{PDB2|1UYK}}, {{PDB2|1UYL}}, {{PDB2|1UYM}}, {{PDB2|1Y4S}}, {{PDB2|1Y4U}}, {{PDB2|1YC3}}, {{PDB2|1YER}}, {{PDB2|1YES}}, {{PDB2|1YET}}, {{PDB2|1YSZ}}, {{PDB2|1YT0}}, {{PDB2|1YT1}}, {{PDB2|1YT1}}, {{PDB2|1YT2}}, {{PDB2|1ZW9}}, {{PDB2|1ZWH}}, {{PDB2|2AKP}}, {{PDB2|2BRC}}, {{PDB2|2BRE}}, {{PDB2|2BSM}}, {{PDB2|2BT0}}, {{PDB2|2BYH}}, {{PDB2|2BYI}}, {{PDB2|2BZ5}}, {{PDB2|2CCS}}, {{PDB2|2CCT}}, {{PDB2|2CCU}}, {{PDB2|2CDD}}, {{PDB2|2CG9}}, {{PDB2|2CGF}}, {{PDB2|2ESA}}, {{PDB2|2EXL}}, {{PDB2|2FWY}}, {{PDB2|2FWZ}}, {{PDB2|2FXS}}, {{PDB2|2FYP}}, {{PDB2|2GFD}}, {{PDB2|2GQP}}, {{PDB2|2H55}}, {{PDB2|2H8M}}, {{PDB2|2HCH}}, {{PDB2|2HG1}}, {{PDB2|2IOP}}, {{PDB2|2IOQ}}, {{PDB2|2IOR}}, {{PDB2|2IWS}}, {{PDB2|2IWU}}, {{PDB2|2IWX}}, {{PDB2|2O1U}}, {{PDB2|2O1V}}, {{PDB2|2O1W}}, {{PDB2|2QF6}}, {{PDB2|2QFO}}, {{PDB2|2QG0}}, {{PDB2|2QG2}}, {{PDB2|2UWD}}, {{PDB2|2VCI}}, {{PDB2|2VCJ}}, {{PDB2|2VWC}}, {{PDB2|3D0B}} }} {{Pfam_box | Symbol = Hsp90 MD | Name = Hsp90 middle domain | Pfam= PF00183 | InterPro= IPR001404 | SMART= | PROSITE = PDOC00270 | SCOP = d.14.1.8 | SCOP = 1hk7 | TCDB = | PDB = {{PDB2|1HK7}}, {{PDB2|1USU}}, {{PDB2|1USV}}, {{PDB2|1Y4S}}, {{PDB2|1Y4U}}, {{PDB2|2CG9}}, {{PDB2|2CGE}}, {{PDB2|2GQ0}}, {{PDB2|2IOP}}, {{PDB2|2IOQ}}, {{PDB2|2O1T}}, {{PDB2|2O1U}}, {{PDB2|2O1V}}, {{PDB2|2O1W}} }} {{Pfam_box | Symbol = Hsp90 CTD | Name = Hsp90 C-terminal domain | Pfam= PF00183 | InterPro= IPR001404 | SMART= | PROSITE = PDOC00270 | SCOP = d.271.1.1 | SCOP = 1sf8 | TCDB = | PDB = {{PDB2|1SF8}}, {{PDB2|2CG9}}, {{PDB2|2CGE}}, {{PDB2|2IOP}}, {{PDB2|2IOQ}}, {{PDB2|2O1T}}, {{PDB2|2O1U}}, {{PDB2|2O1V}}, {{PDB2|2O1W}} }} '''Hsp90''' ('''heat shock protein 90''') is a molecular [[chaperone (protein)|chaperone]] and is one of the most abundant [[protein]]s expressed in [[cell (biology)|cell]]s.<ref name="pmid9749880">{{cite journal | author = Csermely P, Schnaider T, Soti C, Prohászka Z, Nardai G | title = The 90-kDa molecular chaperone family: structure, function, and clinical applications. A comprehensive review | journal = Pharmacol. Ther. | volume = 79 | issue = 2 | pages = 129–68 | year = 1998 | month = August | pmid = 9749880 | doi = 10.1016/S0163-7258(98)00013-8 | url = | issn = }}</ref> It is a member the [[heat shock protein]] family which is upregulated in response to stress. Hsp90 is found in [[eubacteria]] and all branches of [[eukarya]], but it is apparently absent in [[archaea]].<ref name="R20">{{cite journal | author = Chen B, Zhong D, Monteiro A | title = Comparative genomics and evolution of the Hsp90 family of genes across all kingdoms of organisms | journal = BMC Genomics | volume = 7 | issue = | pages = 156 | year = 2006 | pmid = 16780600 | pmc = 1525184 | doi = 10.1186/1471-2164-7-156 | url = }}</ref> Whereas cytoplasmic Hsp90 is essential for viability under all conditions in [[eukaryote]]s, the bacterial homologue '''HtpG''' is dispensable under non-heat stress conditions.<ref name="pmid9748451">{{cite journal | author = Thomas JG, Baneyx F | title = Roles of the Escherichia coli small heat shock proteins IbpA and IbpB in thermal stress management: comparison with ClpA, ClpB, and HtpG In vivo | journal = J. Bacteriol. | volume = 180 | issue = 19 | pages = 5165–72 | year = 1998 | month = October | pmid = 9748451 | pmc = 107554 | url = | issn = }}</ref> ==Introduction== Heat shock proteins, as a class, are among the most highly expressed cellular proteins across all species. As their name implies, heat shock proteins protect cells when stressed by elevated temperatures. They account for 1–2% of total protein in unstressed cells. However when cells are heated, the fraction of heat shock proteins increases to 4–6% of cellular proteins.<ref name="R1">{{cite journal | author = Crevel G, Bates H, Huikeshoven H, Cotterill S | title = The Drosophila Dpit47 protein is a nuclear Hsp90 co-chaperone that interacts with DNA polymerase alpha | journal = J. Cell. Sci. | volume = 114 | issue = Pt 11 | pages = 2015–25 | year = 2001 | month = June | pmid = 11493638 | url = http://jcs.biologists.org/cgi/pmidlookup?view=long&pmid=11493638 | issn = }}</ref> Heat shock protein 90 (Hsp90) is one of the most common of the heat related proteins. The protein is named "HSP" for obvious reasons whereas the "90" comes from the fact that it weighs roughly 90 [[Atomic mass unit|kiloDaltons]]. A 90 kD size protein is considered a fairly large for a non-fibrous protein. The function of Hsp90 includes assisting in [[protein folding]], cell [[signal transduction|signaling]], and [[tumor]] repression. This protein was first isolated by extracting proteins from stressed cells. These cells were stressed by heating, dehydrating or by other means, all of which caused the cell’s proteins to begin to [[denaturation (biochemistry)|denature]].<ref name="R4">{{cite journal | author = Prodromou C, Panaretou B, Chohan S, Siligardi G, O'Brien R, Ladbury JE, Roe SM, Piper PW, Pearl LH | title = The ATPase cycle of Hsp90 drives a molecular 'clamp' via transient dimerization of the N-terminal domains | journal = EMBO J. | volume = 19 | issue = 16 | pages = 4383–92 | year = 2000 | month = August | pmid = 10944121 | pmc = 302038 | doi = 10.1093/emboj/19.16.4383 | url = }}</ref> As discussed in more detail below, researchers later realized that Hsp90 has other essential functions in unstressed cells. ==Isoforms== Hsp90 is highly conserved and expressed in a variety of different organisms from bacteria to mammals – including the prokaryotic analogue [[htpG]] (high temperature protein G) with 40% sequence identity and 55% similarity to the human protein.<ref name="R20"/> [[Yeast]] Hsp90 is 60% identical to human Hsp90α. In [[mammal]]ian cells, there are two or more genes encoding [[cytosol]]ic Hsp90 homologues,<ref name="R20"/> with the human Hsp90α showing 85% sequence identity to Hsp90β.<ref name="pmid16269234">{{cite journal | author = Chen B, Piel WH, Gui L, Bruford E, Monteiro A | title = The Hsp90 family of genes in the human genome: insights into their divergence and evolution | journal = Genomics | volume = 86 | issue = 6 | pages = 627–37 | year = 2005 | month = December | pmid = 16269234 | doi = 10.1016/j.ygeno.2005.08.012 | url = | issn = }}</ref> The α- and the β-forms are thought to be the result of a [[gene duplication]] event that occurred millions of years ago.<ref name="R20"/> The five functional human genes encoding Hsp90 [[protein isoform]]s are listed below:<ref name="pmid16269234"/> {| class="wikitable" |- ! family ! subcellular<br />location ! subfamily ! gene ! protein |- | rowspan="3" | HSP90A | rowspan="3" align="center" | [[cytosol|cytosolic]] | rowspan="2" align="center" | HSP90AA<br />(inducible) | [[HSP90AA1]] | align="center" | Hsp90-α<sub>1</sub> |- | [[HSP90AA2]] | align="center" | Hsp90-α<sub>2</sub> |- | align="center" | HSP90AB<br />(constitutively expressed) | [[HSP90AB1]] | align="center" | Hsp90-β |- | HSP90B | align="center" | [[endoplasmic reticulum|endoplasmic<br />reticulum]] | | align="center" | [[HSP90B1]] | align="center" | GRP94 |- | align="center" | TRAP | [[mitochondrion|mitochondrial]] | | align="center" | [[TRAP1]] | align="center" | '''T'''NF '''R'''eceptor-<br />'''A'''ssociated '''P'''rotein 1 |} There are 12 human [[pseudogene]]s (non-functional genes) that encode additional Hsp90 isoforms which are not expressed as proteins. Recently, a membrane associated variant of cytosolic Hsp90, lacking an ATP-binding site, has been identified and was named '''Hsp90N'''.<ref name="R21">{{cite journal | author = Grammatikakis N, Vultur A, Ramana CV, Siganou A, Schweinfest CW, Watson DK, Raptis L | title = The role of Hsp90N, a new member of the Hsp90 family, in signal transduction and neoplastic transformation | journal = J. Biol. Chem. | volume = 277 | issue = 10 | pages = 8312–20 | year = 2002 | month = March | pmid = 11751906 | doi = 10.1074/jbc.M109200200 | url = }}</ref> Hsp90N is a splice variant of HSP90AA1. ==Structure== ===Common features=== The overall structure of Hsp90 is similar to other proteins in that it contains all of the common [[secondary structure|secondary structural elements]] (i.e., [[alpha helix]]es, [[Beta sheet|beta pleated sheets]] and random coils). Being a [[cytoplasm]]ic protein requires that the protein be globular in structure, that is largely non-polar on the inside and polar on the outside, so as to be dissolved by water. Hsp90 contains nine helices and eight anti-parallel beta pleated sheets, which combine to form several alpha/beta sandwiches. The [[310 helix|3<sub>10</sub> helices]] make up approximately 11% of the protein's amino acid residues, which is much higher than the average 4% in other proteins.<ref name="R2">{{cite journal | author = Goetz MP, Toft DO, Ames MM, Erlichman C | title = The Hsp90 chaperone complex as a novel target for cancer therapy | journal = Ann. Oncol. | volume = 14 | issue = 8 | pages = 1169–76 | year = 2003 | month = August | pmid = 12881371 | url = | doi = 10.1093/annonc/mdg316 }}</ref> ===Domain structure=== [[Image:Hsp90_schematic_2cg9.png|thumb|270px|Domain structure of the yeast heat-inducible Hsp90. '''Top''': 3D structure of the dimeric Hsp90 based on {{PDB|2CG9}} coordinates. Bound ATP molecules are represented by space filling spheres. '''Bottom''': 1D sequence of the yeast Hsp90. NTD= N-terminal domain (red), MD = middle domain (green), CTD = C-terminal domain (blue).]] Hsp90 consists of four structural [[protein domain|domain]]s:<ref name=pearl>{{cite journal | author = Pearl LH, Prodromou C | title = Structure and in vivo function of Hsp90 | journal = Curr. Opin. Struct. Biol. | volume = 10 | issue = 1 | pages = 46–51 | year = 2000 | month = February | pmid = 10679459 | url = | doi = 10.1016/S0959-440X(99)00047-0 }}</ref><ref name=prodromou3>{{cite journal | author = Prodromou C, Pearl LH | title = Structure and functional relationships of Hsp90 | journal = Curr Cancer Drug Targets | volume = 3 | issue = 5 | pages = 301–23 | year = 2003 | month = October | pmid = 14529383 | url = | doi = 10.2174/1568009033481877 }}</ref><ref name=pearl2>{{cite journal | author = Pearl LH, Prodromou C | title = Structure, function, and mechanism of the Hsp90 molecular chaperone | journal = Adv. Protein Chem. | volume = 59 | issue = | pages = 157–86 | year = 2001 | pmid = 11868271 | url = | doi = 10.1016/S0065-3233(01)59005-1 }}</ref> * a highly conserved [[N-terminus|N-terminal]] (NTD) domain of ~25 kDa, * a "charged linker" region, that connects the N-terminus with the middle domain. * a middle domain (MD) of ~40 kDa, * a [[C-terminus|C-terminal]] domain (CTD) of ~12 kDa and [[Crystal structure]]s are available for the N-terminal domain of [[yeast]] and human Hsp90,<ref name=stebbins>{{cite journal | author = Stebbins CE, Russo AA, Schneider C, Rosen N, Hartl FU, Pavletich NP | title = Crystal structure of an Hsp90-geldanamycin complex: targeting of a protein chaperone by an antitumor agent | journal = Cell | volume = 89 | issue = 2 | pages = 239–50 | year = 1997 | month = April | pmid = 9108479 | url = | doi = 10.1016/S0092-8674(00)80203-2 }}</ref><ref name=prodromou1>{{cite journal | author = Prodromou C, Roe SM, O'Brien R, Ladbury JE, Piper PW, Pearl LH | title = Identification and structural characterization of the ATP/ADP-binding site in the Hsp90 molecular chaperone | journal = Cell | volume = 90 | issue = 1 | pages = 65–75 | year = 1997 | month = July | pmid = 9230303 | url = | doi = 10.1016/S0092-8674(00)80314-1 }}</ref><ref name=prodromou2>{{cite journal | author = Prodromou C, Roe SM, Piper PW, Pearl LH | title = A molecular clamp in the crystal structure of the N-terminal domain of the yeast Hsp90 chaperone | journal = Nat. Struct. Biol. | volume = 4 | issue = 6 | pages = 477–82 | year = 1997 | month = June | pmid = 9187656 | url = | doi = 10.1038/nsb0697-477 }}</ref> for complexes of the N-terminus with inhibitors and [[nucleotide]]s,<ref name=stebbins/><ref name=prodromou1/> and for the middle domain of yeast Hsp90.<ref name=meyer>{{cite journal | author = Meyer P, Prodromou C, Hu B, Vaughan C, Roe SM, Panaretou B, Piper PW, Pearl LH | title = Structural and functional analysis of the middle segment of hsp90: implications for ATP hydrolysis and client protein and cochaperone interactions | journal = Mol. Cell | volume = 11 | issue = 3 | pages = 647–58 | year = 2003 | month = March | pmid = 12667448 | url = | doi = 10.1016/S1097-2765(03)00065-0 }}</ref> Recently structures for full length Hsp90 from ''E. coli'' ({{PDB2|2IOP}}, {{PDB2|2IOQ}}),<ref name="pmid17055434">{{cite journal | author = Shiau AK, Harris SF, Southworth DR, Agard DA | title = Structural Analysis of E. coli hsp90 reveals dramatic nucleotide-dependent conformational rearrangements | journal = Cell | volume = 127 | issue = 2 | pages = 329–40 | year = 2006 | month = October | pmid = 17055434 | doi = 10.1016/j.cell.2006.09.027 | url = | issn = }}</ref> yeast ({{PDB2|2CG9}}, {{PDB2|2CGE}}),<ref name=ali>{{cite journal | author = Ali MM, Roe SM, Vaughan CK, Meyer P, Panaretou B, Piper PW, Prodromou C, Pearl LH' | title = Crystal structure of an Hsp90-nucleotide-p23/Sba1 closed chaperone complex | journal = Nature | volume = 440 | issue = 7087 | pages = 1013–7 | year = 2006 | month = April | pmid = 16625188 | doi = 10.1038/nature04716 | url = }}</ref> and the dog endoplasmic reticulum ({{PDB2|2O1U}}, {{PDB2|2O1V}})<ref name="pmid17936703">{{cite journal | author = Dollins DE, Warren JJ, Immormino RM, Gewirth DT | title = Structures of GRP94-nucleotide complexes reveal mechanistic differences between the hsp90 chaperones | journal = Mol. Cell | volume = 28 | issue = 1 | pages = 41–56 | year = 2007 | month = October | pmid = 17936703 | doi = 10.1016/j.molcel.2007.08.024 | url = | issn = }}</ref> were elucidated.<ref name="pmid18442971">{{cite journal | author = Wandinger SK, Richter K, Buchner J | title = The hsp90 chaperone machinery | journal = J. Biol. Chem. | volume = 283 | issue = 27 | pages = 18473–7 | year = 2008 | month = July | pmid = 18442971 | doi = 10.1074/jbc.R800007200 | url = | issn = }}</ref> Hsp90 forms [[homodimer]]s where the contact sites are localized within the C-terminus in the open conformation of the dimer. The N-termini also come in contact in the closed conformation of the dimer.<ref name=meyer2>{{cite journal | author = Meyer P, Prodromou C, Hu B, Vaughan C, Roe SM, Panaretou B, Piper PW, Pearl LH. | title = Structural and functional analysis of the middle segment of hsp90: implications for ATP hydrolysis and client protein and cochaperone interactions | journal = Mol. Cell | volume = 11 | issue = 3 | pages = 647–58 | year = 2003 | month = March | pmid = 12667448 | url = | doi = 10.1016/S1097-2765(03)00065-0 }}</ref> ====N-terminal domain==== [[Image:Hsp90 ATP pocket.jpg|thumb|270px|The ATP binding pocket.]] The N-terminal domain shows high [[homology (biology)|homology]] not only amongst members of the Hsp90 chaperone family, but also to members of the ATPase/kinase GHKL ([[DNA gyrase|'''G'''yrase]], '''H'''sp90, [[Histidine kinase|Histidine '''K'''inase]], [[DNA mismatch repair#MutL|'''M'''utL]]) superfamily.<ref name=prodromou3/> A common binding pocket for ATP and the inhibitor [[geldanamycin]] is situated in the N-terminal domain.<ref name=stebbins/><ref name=prodromou1/> Amino acids that are directly involved in the interaction with ATP are Leu34, Asn37, Asp79, Asn92, Lys98, Gly121, and Phe124. In addition, Mg<sup>2+</sup> and a several water molecules form bridging electrostatic and [[hydrogen bond|hydrogen bonding]] interactions respectively between Hsp90 and ATP. In adddition, Glu33 is required for ATP [[hydrolysis]]. ====Middle domain==== The middle domain is divided into three regions: *a 3-layer α-β-α sandwich, *a 3-turn α-helix and irregular loops, and *a 6-turn α-helix.<ref name=prodromou3/> The MD is also involved in client protein binding. For example proteins known to interact this the Hsp90 MD include PKB/[[Akt1]], [[nitric oxide synthase|eNOS]],<ref name=sato/><ref name=fontana>{{cite journal | author = Fontana J, Fulton D, Chen Y, Fairchild TA, McCabe TJ, Fujita N, Tsuruo T, Sessa WC | title = Domain mapping studies reveal that the M domain of hsp90 serves as a molecular scaffold to regulate Akt-dependent phosphorylation of endothelial nitric oxide synthase and NO release | journal = Circ. Res. | volume = 90 | issue = 8 | pages = 866–73 | year = 2002 | month = May | pmid = 11988487 | url = | doi = 10.1161/01.RES.0000016837.26733.BE }}</ref> [[AHSA1|Aha1]], [[AHSA2|Hch1]]. Furthermore substrate binding (e.g., by Aha1 and Hch1) to the MD is also known to increase the [[ATPase]] activity of Hsp90.<ref name="meyer"/><ref name=panaretou>{{cite journal | author = Panaretou B, Siligardi G, Meyer P, Maloney A, Sullivan JK, Singh S, Millson SH, Clarke PA, Naaby-Hansen S, Stein R, Cramer R, Mollapour M, Workman P, Piper PW, Pearl LH, Prodromou C | title = Activation of the ATPase activity of hsp90 by the stress-regulated cochaperone aha1 | journal = Mol. Cell | volume = 10 | issue = 6 | pages = 1307–18 | year = 2002 | month = December | pmid = 12504007 | url = | doi = 10.1016/S1097-2765(02)00785-2 }}</ref> ====C-terminal domain==== The C-terminal domain possesses an alternative ATP-binding site, which becomes accessible when the N-terminal Bergerat pocket is occupied.<ref name=marcu>{{cite journal | author = Marcu MG, Chadli A, Bouhouche I, Catelli M, Neckers LM | title = The heat shock protein 90 antagonist novobiocin interacts with a previously unrecognized ATP-binding domain in the carboxyl terminus of the chaperone | journal = J. Biol. Chem. | volume = 275 | issue = 47 | pages = 37181–6 | year = 2000 | month = November | pmid = 10945979 | doi = 10.1074/jbc.M003701200 | url = }}</ref><ref name=söti>{{cite journal | author = Söti C, Rácz A, Csermely P | title = A Nucleotide-dependent molecular switch controls ATP binding at the C-terminal domain of Hsp90. N-terminal nucleotide binding unmasks a C-terminal binding pocket | journal = J. Biol. Chem. | volume = 277 | issue = 9 | pages = 7066–75 | year = 2002 | month = March | pmid = 11751878 | doi = 10.1074/jbc.M105568200 | url = }}</ref> At the very C-terminal end of the protein is the tetratricopeptide repeat (TPR) motif recognition site, the conserved MEEVD pentapeptide, that is responsible for the interaction with co-factors such as the [[immunophilin]]s [[FKBP5|FKBP51]] and [[FKBP52]], the [[STIP1|stress induced phosphoprotein 1]] (Sti1/Hop), [[PPID|cyclophilin-40]], [[TFPI2|PP5]], [[TOMM70A|Tom70]], and many more.<ref name=young>{{cite journal | author = Young JC, Obermann WM, Hartl FU | title = Specific binding of tetratricopeptide repeat proteins to the C-terminal 12-kDa domain of hsp90 | journal = J. Biol. Chem. | volume = 273 | issue = 29 | pages = 18007–10 | year = 1998 | month = July | pmid = 9660753 | url = | doi = 10.1074/jbc.273.29.18007 }}</ref> ==Mechanism== The Hsp90 protein contains three functional domains, the [[Adenosine triphosphate|ATP]] binding, protein binding and dimerizing domain, each of which play a crucial role in the function of the protein. ===ATP binding=== [[Image:Hsp_90_pincer_movement.png|thumb|280px|Pincer movement of Hsp90 coupled to the ATPase cycle.]] The region of the protein near the [[N-terminus]] has a high affinity ATP binding site. The ATP binds to a sizable cleft in the side of protein, which is 15&nbsp;[[Ångström|Å]] (1.5&nbsp;nanometres) deep. This cleft has a high affinity for ATP, and when given a suitable protein substrate, Hsp90 cleaves the ATP into [[Adenosine diphosphate|ADP]] and [[phosphate|P<sub>i</sub>]]. Direct inhibitors of ATP binding or [[allosteric]] inhibitors of either ATP binding or ATPase activity can block Hsp90 function.<ref name="R2"> </ref> Another interesting feature of the ATP-binding region of Hsp90 is that it has a “lid” that is open during the ADP-bound state and closed in the ATP-bound state, in the open conformation, the lid has no intraprotein interaction, and when closed comes into contact with several residues.<ref name="R6">{{cite journal | author = Wegele H, Müller L, Buchner J | title = Hsp70 and Hsp90--a relay team for protein folding | journal = Rev. Physiol. Biochem. Pharmacol. | volume = 151 | issue = | pages = 1–44 | year = 2004 | pmid = 14740253 | doi = 10.1007/s10254-003-0021-1 | url = }}</ref> The contribution of this lid to the activity of Hsp90 has been probed with [[site-directed mutagenesis]]. The Ala107Asp mutant stabilizing the closed conformation of the protein through the formation of additional hydrogen bonds substantially increases ATPase activity while leaving the AMP+PnP conformation unchanged.<ref name="R6"/> The [[ATPase]] binding region of Hsp90 is currently under intense study, because it is the principal binding site of drugs targeting this protein.<ref name="pmid16784024">{{cite journal | author = Chiosis G, Caldas Lopes E, Solit D | title = Heat shock protein-90 inhibitors: a chronicle from geldanamycin to today's agents | journal = Curr Opin Investig Drugs | volume = 7 | issue = 6 | pages = 534–41 | year = 2006 | month = June | pmid = 16784024 | doi = | url = | issn = }}</ref> Antitumor drugs targeting this section of Hsp90 include the antibiotics [[geldanamycin]],<ref name="R2"/><ref name="R3">{{cite journal | author = Pratt WB, Toft DO | title = Regulation of signaling protein function and trafficking by the hsp90/hsp70-based chaperone machinery | journal = Exp. Biol. Med. (Maywood) | volume = 228 | issue = 2 | pages = 111–33 | year = 2003 | month = February | pmid = 12563018 | url = http://www.ebmonline.org/cgi/pmidlookup?view=long&pmid=12563018 | issn = }}</ref> [[herbimycin]], [[radicicol]], [[deguelin]],<ref name="Oh">{{cite journal | author =Oh SH, Woo JK, Yazici YD, Myers JN, Kim WY, Jin Q, Hong SS, Park HJ, Suh YG, Kim KW, Hong WK, Lee HY | title = Structural basis for depletion of heat shock protein 90 client proteins by deguelin | journal = J. Natl. Cancer Inst. | volume = 99 | issue = 12 | pages = 949–61 | year = 2007 | month = June | pmid = 17565155 | doi = 10.1093/jnci/djm007 | url = }}</ref>, [[derrubone]],<ref name="Hadden">{{cite journal | author = Hadden MK, Galam L, Gestwicki JE, Matts RL, Blagg BS | title = Derrubone, an inhibitor of the Hsp90 protein folding machinery | journal = J. Nat. Prod. | volume = 70 | issue = 12 | pages = 2014–8 | year = 2007 | month = December | pmid = 18020309 | doi = 10.1021/np070190s | url = }}</ref> and [[macbecin]].<ref name="Martin">{{cite journal | author = Martin CJ, Gaisser S, Challis IR, Carletti I, Wilkinson B, Gregory M, Prodromou C, Roe SM, Pearl LH, Boyd SM, Zhang MQ | title = Molecular characterization of macbecin as an Hsp90 inhibitor | journal = J. Med. Chem. | volume = 51 | issue = 9 | pages = 2853–7 | year = 2008 | month = May | pmid = 18357975 | doi = 10.1021/jm701558c | url = }}</ref> ===Protein binding=== [[Image:hsp90cycle.jpg|thumb|280px|The Hsp90 chaperone cycle. X/Y represents an immature incompletely folded protein such a [[steroid receptor]]. [[DNAJB1|Hsp40]], [[Hsp70]], and [[PTGES3|p23]] are partner chaperones while [[Hop (protein)|Hop]] is a [[co-chaperone]]. Finally X-X represents a mature properly folded protein dimer.]] <!-- Unsourced image removed: [[Image:hsp90_5.jpg]] -->The protein binding region of Hsp90 is located towards the [[C-terminus]] of the amino sequence. The Hsp90 protein can adopt two major conformational states. The first is an open ATP-bound state and the second is a closed ADP-bound state. Thus ATP hydrolysis drives what is commonly referred to as a “pincer type” conformational change in the protein binding site.<ref name="R9">{{cite journal | author = Grenert JP, Sullivan WP, Fadden P, Haystead TA, Clark J, Mimnaugh E, Krutzsch H, Ochel HJ, Schulte TW, Sausville E, Neckers LM, Toft DO | title = The amino-terminal domain of heat shock protein 90 (hsp90) that binds geldanamycin is an ATP/ADP switch domain that regulates hsp90 conformation | journal = J. Biol. Chem. | volume = 272 | issue = 38 | pages = 23843–50 | year = 1997 | month = September | pmid = 9295332 | url = | doi = 10.1074/jbc.272.38.23843 }}</ref> Hsp90, while in the open conformation, leaves some [[hydrophobic]] residues exposed, to which unfolded and misfolded proteins that have unusual hydrophobic regions exposed are recruited with high affinity.<ref name="R11">{{cite journal | author = Xu Z, Horwich AL, Sigler PB | title = The crystal structure of the asymmetric GroEL-GroES-(ADP)7 chaperonin complex | journal = Nature | volume = 388 | issue = 6644 | pages = 741–50 | year = 1997 | month = August | pmid = 9285585 | doi = 10.1038/41944 | url = | issn = }}</ref> When a bound substrate is in place, the energy releasing ATP hydrolysis by the ATPase function near the NTD forces conformational changes which clamps the Hsp90 down onto the substrate.<ref name="R6"/> In a reaction similar to that of other molecular clamp proteins like GyrB and [[DNA mismatch repair#MutL|MutL]], this site drives virtually all of the protein folding functions that Hsp90 plays a role in. In contrast MutL and GyrB function as [[topoisomerase]]s and use a charge clamp with a high amount of positively charged sidechains that is electrostatically attracted to the negative backbone of DNA.<ref name="R10">{{cite journal | author = Kampranis SC, Bates AD, Maxwell A | title = A model for the mechanism of strand passage by DNA gyrase | journal = Proc. Natl. Acad. Sci. U.S.A. | volume = 96 | issue = 15 | pages = 8414–9 | year = 1999 | month = July | pmid = 10411889 | pmc = 17530 | url = | doi = 10.1073/pnas.96.15.8414 }}</ref> The ability of Hsp90 to clamp onto proteins allows it perform several functions including assisting folding, preventing aggregation, and facilitating transport. ==Function== ===Normal cells=== In unstressed cells, Hsp90 plays a number of important roles, which include assisting in [[protein folding|folding]], intracellular transport, maintenance, and degradation of proteins as well as facilitating cell signaling. ====Protein folding and chaperon==== Hsp90 is known to associate with the non-native structures of many proteins which has lead to the proposal that Hsp90 is involved in protein folding in general.<ref name="pmid10322418">{{cite journal | author = Buchner J | title = Hsp90 & Co. - a holding for folding | journal = Trends Biochem. Sci. | volume = 24 | issue = 4 | pages = 136–41 | year = 1999 | month = April | pmid = 10322418 | doi = 10.1016/S0968-0004(99)01373-0 | url = | issn = }}</ref> Furthermore Hsp90 has been shown to suppress the aggregation of a wide range of "client" or "substrate" proteins and hence acts as a general protective chaperone.<ref name="pmid1551911">{{cite journal | author = Miyata Y, Yahara I | title = The 90-kDa heat shock protein, Hsp90, binds and protects casein kinase II from self-aggregation and enhances its kinase activity | journal = J. Biol. Chem. | volume = 267 | issue = 10 | pages = 7042–7 | year = 1992 | month = April | pmid = 1551911 | doi = | url = http://www.jbc.org/cgi/content/abstract/267/10/7042 | issn = }}</ref><ref name="pmid1614549">{{cite journal | author = Wiech H, Buchner J, Zimmermann R, Jakob U | title = Hsp90 chaperones protein folding in vitro | journal = Nature | volume = 358 | issue = 6382 | pages = 169–70 | year = 1992 | month = July | pmid = 1614549 | doi = 10.1038/358169a0 | url = | issn = }}</ref><ref name="pmid7706269">{{cite journal | author = Jakob U, Lilie H, Meyer I, Buchner J | title = Transient interaction of Hsp90 with early unfolding intermediates of citrate synthase. Implications for heat shock in vivo | journal = J. Biol. Chem. | volume = 270 | issue = 13 | pages = 7288–94 | year = 1995 | month = March | pmid = 7706269 | doi = 10.1074/jbc.270.13.7288 | url = | issn = }}</ref> However Hsp90 is somewhat more selective than other chaperones.<ref name="pmid12475174">{{cite journal | author = Picard D | title = Heat-shock protein 90, a chaperone for folding and regulation | journal = Cell. Mol. Life Sci. | volume = 59 | issue = 10 | pages = 1640–8 | year = 2002 | month = October | pmid = 12475174 | doi = 10.1007/PL00012491 | url = | issn = }}</ref> ====Protein degradation==== <!-- Image with unknown copyright status removed: [[Image:hsp903=4.jpg]] --> Eukaryotic proteins which are no longer needed or are misfolded or otherwise damaged are usually marked for destruction by the [[Ubiquitin|polyubiquitation]] pathway. These ubiquitinated proteins are recognized and degraded by the 26S [[proteasome]].<ref name="R7">{{cite journal | author = Imai J, Maruya M, Yashiroda H, Yahara I, Tanaka K | title = The molecular chaperone Hsp90 plays a role in the assembly and maintenance of the 26S proteasome | journal = EMBO J. | volume = 22 | issue = 14 | pages = 3557–67 | year = 2003 | month = July | pmid = 12853471 | pmc = 165619 | doi = 10.1093/emboj/cdg349 | url = }}</ref><ref name="R16">{{cite journal | author = Correia MA, Sadeghi S, Mundo-Paredes E | title = Cytochrome P450 ubiquitination: branding for the proteolytic slaughter? | journal = Annu. Rev. Pharmacol. Toxicol. | volume = 45 | issue = | pages = 439–64 | year = 2005 | pmid = 15822184 | doi = 10.1146/annurev.pharmtox.45.120403.100127 | url = }}</ref> Hence the 26S proteasome is an integral part of the cell's mechanism to degrade proteins. Furthermore a constant supply of functional Hsp90 needed to maintain the [[tertiary structure]] of the proteasome.<ref name="R14">{{cite journal | author = Kimura Y, Matsumoto S, Yahara I | title = Temperature-sensitive mutants of hsp82 of the budding yeast Saccharomyces cerevisiae | journal = Mol. Gen. Genet. | volume = 242 | issue = 5 | pages = 517–27 | year = 1994 | month = March | pmid = 8121410 | url = | doi = 10.1007/BF00285275 }}</ref> Finally experiments done with heat sensitive Hsp90 mutants and the 26S proteasome suggest that Hsp90 is responsible for most, if not all, of the ATPase activity of the proteasome.<ref name="R7"/> ====Interaction with steroid receptors==== [[Image:gr_hsp90_translocation.png|thumb|405px|Schematic diagram of the translocation of the [[glucocorticoid receptor]] (GR) from the cytoplasm into the nucleus assisted by Hsp90 (90).<ref name="pmid11751894">{{cite journal | author = Davies TH, Ning YM, Sánchez ER | title = A new first step in activation of steroid receptors: hormone-induced switching of FKBP51 and FKBP52 immunophilins | journal = J. Biol. Chem. | volume = 277 | issue = 7 | pages = 4597–600 | year = 2002 | month = February | pmid = 11751894 | doi = 10.1074/jbc.C100531200 | url = | issn = }}</ref> In the cytoplasm, GR is complexed with Hsp90 and the [[immunophilin]] [[FKBP5|FKBP51]] (51). Binding of hormone to GR causes a conformational change in the complex which results in exchange of FKBP51 for [[FKBP52]] (52). FKBP52 in turn binds the [[dynein]] (dyn) motor protein which attaches to the [[cytoskeleton]] and transports the GR complex into the nucleus. Once in the nucleus, the complex disassembles releasing GR which dimerizes and binds to DNA where it facilitates transcription of DNA into [[messenger RNA|mRNA]].]] The [[glucocorticoid receptor]] (GR) is the most thoroughly studied example of a [[steroid receptor]] whose function is crucially dependent on interactions with Hsp90.<ref name="pmid16610357">{{cite journal | author = Pratt WB, Morishima Y, Murphy M, Harrell M | title = Chaperoning of glucocorticoid receptors | journal = Handb Exp Pharmacol | volume = | issue = 172 | pages = 111–38 | year = 2006 | pmid = 16610357 | doi = 10.1007/3-540-29717-0_5 | url = | issn = }}</ref><ref name="pmid17628337">{{cite journal | author = Grad I, Picard D | title = The glucocorticoid responses are shaped by molecular chaperones | journal = Mol. Cell. Endocrinol. | volume = 275 | issue = 1-2 | pages = 2–12 | year = 2007 | month = September | pmid = 17628337 | doi = 10.1016/j.mce.2007.05.018 | url = | issn = }}</ref> In the absence of the steroid hormone [[cortisol]], GR resides in the [[cytosol]] complexed with several chaperone proteins including Hsp90 (see figure to the right). These chaperones maintain the GR in a state capable of binding hormone. A second role of Hsp90 is to bind [[immunophilin]]s (e.g., [[FKBP52]]) that attach the GR complex to the [[dynein]] protein trafficking pathway which [[protein targeting|translocates]] the activated receptor from the cytoplasm into the nucleus.<ref name="pmid15242338">{{cite journal | author = Pratt WB, Galigniana MD, Morishima Y, Murphy PJ | title = Role of molecular chaperones in steroid receptor action | journal = Essays Biochem. | volume = 40 | issue = | pages = 41–58 | year = 2004 | pmid = 15242338 | doi = | url = http://essays.biochemistry.org/bsessays/040/bse0400041.htm | issn = }}</ref> Once in the nucleus, the GR dimerizes and binds to specific sequences of DNA and thereby [[downregulation and upregulation|upregulates]] the expression of GR responsive genes. Hsp90 is also required for the proper functioning of several other steroid receptors, including those responsible for the binding of [[mineralocorticoid receptor|aldosterone]],<ref name="pmid2542305">{{cite journal | author = Rafestin-Oblin ME, Couette B, Radanyi C, Lombes M, Baulieu EE | title = Mineralocorticosteroid receptor of the chick intestine. Oligomeric structure and transformation | journal = J. Biol. Chem. | volume = 264 | issue = 16 | pages = 9304–9 | year = 1989 | month = June | pmid = 2542305 | doi = | url = http://www.jbc.org/cgi/content/abstract/264/16/9304 | issn = }}</ref> [[androgen receptor|androgen]],<ref name="pmid6201744">{{cite journal | author =Joab I, Radanyi C, Renoir M, Buchou T, Catelli MG, Binart N, Mester J, Baulieu EE | title = Common non-hormone binding component in non-transformed chick oviduct receptors of four steroid hormones | journal = Nature | volume = 308 | issue = 5962 | pages = 850–3 | year = 1984 | pmid = 6201744 | doi = 10.1038/308850a0 | url = | issn = }}</ref> [[estrogen receptor|estrogen]],<ref name="pmid3584104">{{cite journal | author = Redeuilh G, Moncharmont B, Secco C, Baulieu EE | title = Subunit composition of the molybdate-stabilized "8-9 S" nontransformed estradiol receptor purified from calf uterus | journal = J. Biol. Chem. | volume = 262 | issue = 15 | pages = 6969–75 | year = 1987 | month = May | pmid = 3584104 | doi = | url = http://www.jbc.org/cgi/content/abstract/262/15/6969 | issn = }}</ref> and [[progesterone receptor|progesterone]].<ref name="pmid2419124">{{cite journal | author = Catelli MG, Binart N, Jung-Testas I, Renoir JM, Baulieu EE, Feramisco JR, Welch WJ | title = The common 90-kd protein component of non-transformed '8S' steroid receptors is a heat-shock protein | journal = EMBO J. | volume = 4 | issue = 12 | pages = 3131–5 | year = 1985 | month = December | pmid = 2419124 | pmc = 554632 | doi = | url = | issn = }}</ref> ===Cancerous cells=== Cancerous cells over express a number of proteins, including [[phosphoinositide 3-kinase|PI3K]] and [[AKT]] and inhibition of these two proteins triggers [[apoptosis]]. Furthermore Hsp90 stabilizes the PI3K and AKT proteins. Hence inhibition of Hsp90 appears to induce [[apoptosis]] through inhibition of the PI3K/AKT signaling pathway.<ref name="pmid15710948">{{cite journal | author = Mohsin SK, Weiss HL, Gutierrez MC, Chamness GC, Schiff R, Digiovanna MP, Wang CX, Hilsenbeck SG, Osborne CK, Allred DC, Elledge R, Chang JC | title = Neoadjuvant trastuzumab induces apoptosis in primary breast cancers | journal = J. Clin. Oncol. | volume = 23 | issue = 11 | pages = 2460–8 | year = 2005 | month = April | pmid = 15710948 | doi = 10.1200/JCO.2005.00.661 | url = }}</ref><ref name="R5">{{cite journal | author = Stebbins CE, Russo AA, Schneider C, Rosen N, Hartl FU, Pavletich NP | title = Crystal structure of an Hsp90-geldanamycin complex: targeting of a protein chaperone by an antitumor agent | journal = Cell | volume = 89 | issue = 2 | pages = 239–50 | year = 1997 | month = April | pmid = 9108479 | url = | doi = 10.1016/S0092-8674(00)80203-2 }}</ref> Another important role of Hsp90 in cancer is the stabilization of mutant proteins such as [[v-Src]], the fusion [[oncogene]] [[Bcr-abl fusion protein|Bcr/Abl]], and [[p53]] that appear during cell transformation. It appears that Hsp90 can act as a "protector" of less stable proteins produced by DNA mutations.<ref name=calderwood>{{cite journal | author = Calderwood SK, Khaleque MA, Sawyer DB, Ciocca DR | title = Heat shock proteins in cancer: chaperones of tumorigenesis | journal = Trends Biochem. Sci. | volume = 31 | issue = 3 | pages = 164–72 | year = 2006 | month = March | pmid = 16483782 | doi = 10.1016/j.tibs.2006.01.006 | url = }}</ref> Hsp90 is also required for induction of vascular endothelial growth factor ([[VEGF]]) and [[nitric oxide synthase]] (NOS).<ref name="fontana"/><ref name="pmid11988487">{{cite journal | author = Fontana J, Fulton D, Chen Y, Fairchild TA, McCabe TJ, Fujita N, Tsuruo T, Sessa WC | title = Domain mapping studies reveal that the M domain of hsp90 serves as a molecular scaffold to regulate Akt-dependent phosphorylation of endothelial nitric oxide synthase and NO release | journal = Circ. Res. | volume = 90 | issue = 8 | pages = 866–73 | year = 2002 | month = May | pmid = 11988487 | url = | doi = 10.1161/01.RES.0000016837.26733.BE }}</ref> Both are important for ''de novo'' [[angiogenesis]] that is required for tumour growth beyond the limit of diffusion distance of oxygen in tissues.<ref name=calderwood/> It also promotes the invasion step of [[metastasis]] by assisting the [[matrix metalloproteinase]] MMP2.<ref name=eustace>{{cite journal | author = Eustace BK, Sakurai T, Stewart JK, Yimlamai D, Unger C, Zehetmeier C, Lain B, Torella C, Henning SW, Beste G, Scroggins BT, Neckers L, Ilag LL, Jay DG | title = Functional proteomic screens reveal an essential extracellular role for hsp90 alpha in cancer cell invasiveness | journal = Nat. Cell Biol. | volume = 6 | issue = 6 | pages = 507–14 | year = 2004 | month = June | pmid = 15146192 | doi = 10.1038/ncb1131 | url = }}</ref> Together with its co-chaperones, Hsp90 modulates tumour cell apoptosis "mediated through effects on [[AKT]],<ref name=sato>{{cite journal | author = Sato S, Fujita N, Tsuruo T | title = Modulation of Akt kinase activity by binding to Hsp90 | journal = Proc. Natl. Acad. Sci. U.S.A. | volume = 97 | issue = 20 | pages = 10832–7 | year = 2000 | month = September | pmid = 10995457 | pmc = 27109 | doi = 10.1073/pnas.170276797 | url = }}</ref> [[tumor necrosis factor receptor]]s (TNFR) and [[NFκB|nuclear factor-κB]] (NF- κB) function."<ref name=whitesell>{{cite journal | author = Whitesell L, Lindquist SL | title = Hsp90 and the chaperoning of cancer | journal = Nat. Rev. Cancer | volume = 5 | issue = 10 | pages = 761–72 | year = 2005 | month = October | pmid = 16175177 | doi = 10.1038/nrc1716 | url = }}</ref> Finally Hsp90 participates in many key processes in oncogenesis such as self-sufficiency in growth signals, stabilization of mutant proteins, angiogenesis, and metastasis. Targeting Hsp90 with drugs has shown promising effects in clinical trials. For example, the Hsp90 inhibitor, [[geldanamycin]] has been used as an anti-tumor agent with great success, 50% reduction of tumor growth has been realized with doses of geldanamycin.<ref name="R2"> </ref> The drug was originally thought to be a [[kinase]] inhibitor. However it has since been shown to be an Hsp90 inhibitor where it uses a compact conformation to insert itself into the ATP binding site.<ref name="R2"/> ==Summary== It is clear that Hsp90 plays a [[Janus (mythology)|Janus]]-like role in the cell where it is essential for the creation, maintenance, and destruction of proteins. Its normal function is critical to maintaining the health of cells while its dysregulation in contrast may contribute to [[carcinogenesis]]. The ability for the chaperonin to both make the 26S proteasome stable ''[[in vivo]]'' so as to allow the cell to degrade unwanted and/or harmful proteins in a timely manner and to be responsible for allowing tumor causing kinases to persist in the cytoplasm that would normally be broken down by the same proteasome confirms these specific roles and at the same time show its functional diversity. Clinical cancer treatment trials such as those with geldanamycin and its derivatives have put Hsp90's importance into focus and have highlighted the need for full scale research into Hsp90 related pathways. Combined with the interest in Hsp90's ''in vivo'' protein folding functions by [[proteomics]] researchers, this chaperonin will continue to be a research priority for the foreseeable future. ==References== {{Reflist|2}} ==External links== * {{MeshName|Hsp90+Heat-Shock+Proteins}} * {{cite web | url = http://hsp90.org/ | title = Hsp90 web site | author = Didier Picard | authorlink = | coauthors = | date = | format = | work = | publisher = VisibilityWeb | pages = | language = | archiveurl = | archivedate = | quote = A web site for the community of scientists interested in the Hsp90 molecular chaperone machine. | accessdate = 2008-07-07}} {{Chaperones}} [[Category:proteins]] [[Category:Heat shock proteins]] [[de:Hsp90]] [[fr:Hsp90]]