Kinesin 13 4138132 220489634 2008-06-20T02:57:42Z DH85868993 2824367 moved [[M Type Kinesins]] to [[Kinesin 13]]: More current terminology, per talk page The '''Kinesin 13 Family''' are a subfamily of the molecular [[motor proteins]] known as [[kinesin]]s. Most kinesins transport materials or cargo around the cell while traversing along [[microtubule]] [[polymer]] tracks with the help of [[ATP hydrolysis|ATP-hydrolysis]]-created energy. They are easily identified by their three typical structural components including a highly conserved structural domain, catalytic core, and microtubule binding sites. The kinesin 13 family, unlike other kinesins, has an internally positioned motor domain. They were initially named KIF-M because of the unique location of their catalytic core in the middle of the [[polypeptide]] between the N-terminal globular domain and the C-terminal stalk but they are truly special due to their versatile nature. The Kinesin 13 family's molecular mechanism is less understood than other classes of kinesins which have their motor domains at one end of the molecule or the other. They are capable of traveling to both the minus and plus ends of microtubules whereas most motors are unidirectional. Thus they can catalytically [[polymerization|depolymerize]] a microtubule from both ends making it a very efficient process. The prototypical member of the Kinesin 13 family is MCAK (mitotic [[centromere]] associated kinesin). Formerly known as Kif2C or KCM1 this molecule has been shown to be essential to [[mitosis]]. Other members of this class include Kif2A, Kif2B, and Kif24. The exact mechanism of Kinesin 13 activated microtubule depolymerization remains unclear, however, recent biochemical and structural studies revealed some more detailed class specific features enabling researchers to formulate the following model. (Refer to Figure 6 in referenced Ogawa article for illustrated description.) The protein first contacts the side wall of a microtubule. This is not a stable interaction because the convex surface of the catalytic core does not fit to the flat surface of the straight microtubule [[protofilament]]. Steric hindrance between the molecule neck and adjacent protofilament further inhibits full contact between protein and the microtubule and only facilitates one-dimensional [[diffusion]] along the microtubule. At this time, The protein's [[nucleotide binding pocket]] is trapped in an open state so that the structure is not [[hydrolysis|hydrolyzing]] ATP. Once the motor reaches the end of the microtubule, the protofilament spontaneously curves itself allowing motor to make full contact with the [[tubulin]] [[subunit]]. More MCAK molecules collectively bind to the curved region supporting the theory that they do not actively peel away the microtubule but they wait patiently for it to adopt this curved conformation. They stabilize the curved conformation by binding to the end of the microtubule and then catalyze depolymerization. ==References== Ogawa, T., Nitta, R., Okada, Y., and N. Hirokawa (2004) Cell 116: 591-602. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WSN-4BSKPFC-D&_user=423519&_coverDate=02%2F20%2F2004&_fmt=full&_orig=search&_qd=1&_cdi=7051&view=c&_acct=C000020258&_version=1&_urlVersion=0&_userid=423519&md5=e9bbf4940109f931dc67ed73439122cb&ref=full A Common Mechanism for Microtubule Destabilizers—M Type Kinesins Stabilize Curling of the Protofilament Using the Class-Specific Neck and Loops] ==External links== * [http://download.cell.com/supplementarydata/cell/116/4/591/DC1/index.htm Video Illustrations] [[Category:Motor proteins]]