Kinesin Transport Protein

Kinesins are a class of motor proteins found in eukaryotic cells.This protein is coded by KIF1B(Kinesin family member 1B)gene. Kinesins move along microtubule cables powered by the hydrolysis of ATP (thus kinesins are ATPases). The active movement of kinesins supports several cellular functions including mitosis, meiosis and transport of cargo such as axonal transport.

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In the cell, small molecules such as gases and glucose diffuse to where they are needed. Large molecules synthesised in the cell body, intracellular components such as vesicles, and organelles such as mitochondria are too large (and the cytosol too crowded) to diffuse to their destinations. Motor proteins fulfill the role of transporting large cargo about the cell to their required destinations. Kinesins are motor proteins that transport such cargo by walking unidirectionally along microtubule tracks hydrolysing one molecule of adenosine triphosphate (ATP) at each step. It was thought that ATP hydrolysis powered each step, the energy released propelling the head forwards to the next binding site. It now seems that the head diffuses forward and the force of binding to the microtubule is what pulls the cargo along.

Motor proteins travel in a specific direction along a microtubule. This is because the microtubule is polar and the heads only bind to the microtubule in one orientation, while ATP binding gives each step its direction through a process known as neck linker zippering.

Most kinesins walk towards the positive end of a microtubule which, in most cells, entails transporting cargo from the centre of the cell towards the periphery. This form of transport is known as anterograde transport.

A different type of motor protein known as dyneins, move towards the minus end of the microtubule. Thus they transport cargo from the periphery (terminal buttons) of the cell towards the centre (soma). This is known as retrograde transport. Anterograde axoplasmic transport is the fastest of the two transports, moving at a speed of up to 500 mm per day, while retrograde transport moves about half as fast.

Kinesin accomplishes transport by "walking" along a microtubule. Two mechanisms have been proposed to account for this movement.

• In the "hand-over-hand" mechanism, the kinesin heads step past one another, alternating the lead position.
• In the "inchworm" mechanism, one kinesin head always leads, moving forward a step before the trailing head catches up.