Structure
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 depolymerize a microtubule from both ends making it a very efficient process.
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 a model.) 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 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.
Read more about this topic: Kinesin 13
Famous quotes containing the word structure:
“The structure was designed by an old sea captain who believed that the world would end in a flood. He built a home in the traditional shape of the Ark, inverted, with the roof forming the hull of the proposed vessel. The builder expected that the deluge would cause the house to topple and then reverse itself, floating away on its roof until it should land on some new Ararat.”
—For the State of New Jersey, U.S. public relief program (1935-1943)
“The question is still asked of women: “How do you propose to answer the need for child care?” That is an obvious attempt to structure conflict in the old terms. The questions are rather: “If we as a human community want children, how does the total society propose to provide for them?””
—Jean Baker Miller (20th century)
“For the structure that we raise,
Time is with materials filled;
Our to-days and yesterdays
Are the blocks with which we build.”
—Henry Wadsworth Longfellow (1809–1882)