Crescentin
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2008-06-15T16:17:50Z
Muro Bot
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robot Adding: [[it:Crescentina (proteina)]]
[[Image:Crescentin.jpg|thumb|300px|Ribbon diagram and space-filling model of ''Caulobacter vibrioides'' Crescentin created from homology model available at [http://modbase.compbio.ucsf.edu/modbase-cgi-new/model_details.cgi?queryfile=1156808221_140&searchmode=default&filtermode=on&displaymode=moddetail&seq_id=&model_id= Q6IET3]]]
'''Crescentin''' is a [[protein]] which is a [[bacterial]] relative of the [[intermediate filaments]] found in [[eukaryotic cells]]. Just as [[tubulins]] and [[actin]]s, the other major [[Cytoskeleton|cytoskeletal proteins]], have [[prokaryotic]] [[Homology (biology)|homologs]] in, respectively, the [[FtsZ]] and [[MreB]] proteins, intermediate filaments are linked to the crescentin protein.
==Role in cell shape==
Crescentin was recently discovered in the prokaryote ''[[Caulobacter crescentus]]'', an aquatic bacterium which uses its [[crescent]]-shaped cells for enhanced motility.<ref>Biosciences, Eurekah.com, 2000-2005. Accessed [[19 February]]. 2006 through PubMed.</ref> The crescentin protein is located on the [[wiktionary:Concave|concave]] face of these cells and appears to be necessary for their shape, as [[mutants]] lacking the protein form rod-shaped cells.<ref>Møller-Jensen, Jakob, and Löwe, Jan. “Increasing complexity of the bacterial cytoskeleton.” ''Curr. Opin. Cell. Biol.'' 2005 Feb.; 17(1): 75-81.</ref> To influence the shape of the ''Caulobacter'' cells, the [[helices]] of crescentin filaments associate with the [[cytoplasmic]] side of the [[cell membrane]] on one lateral side of the cell. This induces a curved cell shape in younger cells, which are shorter than the helical pitch of crescentin, but induces a spiral shape in older, longer cells.<ref>Margolin, William. “Bacterial shapes: concave coiled coils curve Caulobacter.” ''Curr. Biol''. 2004 Mar.; 14: 242-244.</ref>
==Protein structure==
Like eukaryotic intermediate filaments, crescentin organizes into filaments and is present in a helical structure in the cell. Crescentin is necessary for both shapes of the ''Caulobacter'' prokaryote (vibroid/crescent-shape and helical shape, which it may adopt after a long stationary phase). The crescentin protein has 430 residues; its sequence mostly consists of a pattern of 7 repeated residues which form a coiled-coil structure. The [[DNA]] sequence of the protein has sections very similar to the eukaryotic [[keratin]] and [[lamin]] proteins, mostly involving the coiled-coil structure. Researchers Ausmees et al. recently proved that, like animal intermediate filament proteins, crescentin has a central rod made up of four coiled-coil segments.<ref name="Ausmees, N. et al.">Ausmees, N. et al. “The bacterial cytoskeleton: an intermediate filament-like function in cell shape.” ''Cell''. 2003 [[12 December]];115(6):705-13.</ref> Both intermediate filament and crescentin proteins have a primary sequence including four α-helical segments along with non-α-helical linker domains. An important difference between crescentin and animal intermediate filament proteins is that crescentin lacks certain consensus sequence elements at the ends of the rod domain which are conserved in animal lamin and keratin proteins.<ref>Herrmann, Harald and Aebi, Ueli. “Intermediate filaments: Molecular structure, assembly mechanism, and integration into functionally distinct intracellular scaffolds.” ''Ann. Rev. Biochem.'' 73: 749-789.</ref>
==Assembly of filaments==
Eukaryotic intermediate filament proteins assemble into filaments of 8-15 nm within the cell without the need for energy input, that is, no need for [[Adenosine triphosphate|ATP]] or [[Guanosine triphosphate|GTP]]. Ausmees et al. continued their crescentin research by testing whether the protein could assemble into filaments in this manner ''[[in vitro]]''. They found that crescentin proteins were indeed able to form filaments about 10 nm wide, and that some of these filaments organized laterally into bundles, just as eukaryotic intermediate filaments do.<ref name="Ausmees, N. et al.">Ausmees, N. et al. “The bacterial cytoskeleton: an intermediate filament-like function in cell shape.” ''Cell''. 2003 [[12 December]];115(6):705-13.</ref> The similarity of crescentin protein to intermediate filament proteins suggests an [[evolutionary]] linkage between these two cytoskeletal proteins.
==References==
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{{Cytoskeletal Proteins}}
[[Category:Cytoskeleton]]
[[it:Crescentina (proteina)]]