Kinesin

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The kinesin dimer attaches to, and moves along, microtubules.

Kinesins (the one shown is from PDB code 3kin) and dyneins walk along microtubules dragging their cargo along with them (red: ATP) (bottom: domain that links to the cargos) (more details...)

Kinesin is a class of motor protein dimer found in biological cells. A kinesin attaches to microtubules, and moves along the tubule in order to transport cellular cargo, such as vesicles. Kinesins typically consist of two large globular heads that allow attachment to microtubules, a central coiled region, and a region termed light-chain, which connects the kinesin to the intracellular component to be moved. Most kinesin-related proteins move toward the plus end of the microtubule, as does kinesin itself, but some move toward the minus end.

"Kinesin and Dynein lie at the heart of Microtubule-Based Movement. These are termed Microtubule Associated Proteins (MAPs). These motor MAPs attach both to intracellular components, and to microtubles (MTs), and by moving along the MT they are able to transport the intracellular components, which could be organelles, vesicles, or other components of the cytoskeleton, to where they are required." [1] Kinesin accomplishes transport by essentially "walking" along a microtubule. Two mechanisms were proposed to explain how this movement occurs. In the "hand-over-hand" mechanism, the kinesin heads step over one another, in effect alternating in the role of leading forward. In the "inchworm" mechanism, one kinesin dimer moves forward, with the other one then being dragged forward. Despite some remaining controversy, the mounting evidence points towards the hand-over-hand mechanism as being more likely.

In recent years, it has been found that microtubule-based molecular motors including a number of kinesin motors, are capable of organizing two separate microtubule asters into a metastable structures independent of any external positional cues. This self-organization is in turn dependent on the directionalities of these molecular motors as well as its processivity. It is also dependent on the dynamic instability and stochastic transition of microtubule aster itself. This motor-dependent self-organization ultimately contributed to a centrsome-independent mitotic spindle assembly mechanism.

While many kinesins walk along microtubules toward either the plus or minus ends, the Kinesin 13 family act as regulators of microtubule dynamics. The prototypical member of this family is MCAK (formerly Kif2C, XKCM1, Gene KIF2C) which acts at the ends of microtubule polymers to depolymerize them. The function of MCAK in cells and its mechanism in vitro is currently being investigated by numerous labs.

[edit] See also

• Molecular motors

[edit] External links

• How Kinesin Moves
• Kinesin and Dynein Microtubule Movement
• Biology of the Cell, 4th ed
• The Inner Life of a Cell, video featuring a Kinesin transporting a vesicle