Question

The heads of kinesin-like proteins have fairly closely related amino acid sequences but diverse tail sequences. What is the explanation for this seeming contradiction?

1) The similarity of kinesin-like protein heads and the variation in tails are purely random.
2) The similarity of the heads is explained by their similar roles in interacting with microtubules; the variation in the tails reflects the variety of cargoes to which they bind.
3) The similarity of the heads is explained by their different roles in interacting with microtubules; the variation in the tails reflects the similar cargoes to which they bind.
4) The similarity of the heads is explained by their similar roles in interacting with microtubules; the variation in the tails reflects the similar cargoes to which they bind.
5) The similarity of the heads is explained by their different roles in interacting with microtubules; the variation in the tails reflects the variety of cargoes to which they bind.

Answer 1

The heads of kinesin-like proteins have similar amino acid sequences due to their conserved role in interacting with microtubules, while the diversity in their tail sequences is because they bind to a variety of cargoes, requiring adaptation in their tail structures.

Step-by-step explanation:

The observation that kinesin-like protein heads have closely related amino acid sequences while their tails are diverse can be explained by their functional roles within the cell. The similarity of the heads is due to their involvement in interacting with microtubules, a role that is conserved across different kinesin proteins. On the other hand, the variation in their tails is related to the variety of cargoes they bind to, which requires a diverse set of tail domain structures to accommodate different types of cargo that need to be transported within the cell.

Therefore, the correct explanation for this observation is that the similarity of the heads is explained by their similar roles in interacting with microtubules; the variation in the tails reflects the variety of cargoes to which they bind. This is because the head domain is responsible for the ATP-driven 'walking' along microtubule tracks, a fundamental process that is necessary for the transport functions kinesins serve, whereas the tail domain is adapted to bind different cargoes, necessitating the sequence variability.