Question

If you were comparing the molecular structure of kinesin and myosin, which are thought to have been derived from a common ancestral protein, which part (heads or tails) would you expect to be most similar between them? Why?

Answer 1

The heads of kinesin and myosin are more likely to be similar due to their conserved ATPase activity necessary for their role as motor proteins, while their tails have diverged more significantly. This is analogous to the evolutionary relationship observed between homologous structures like FtsZ and tubulin.

Step-by-step explanation:

Comparing the Molecular Structure of Kinesin and Myosin

When comparing the molecular structures of kinesin and myosin, which are believed to have evolved from a common ancestral protein, we would expect their heads to be more similar than their tails. The reason for this prediction is that the heads of these motor proteins are responsible for ATPase activity and their interaction with other cytoskeletal elements. This is evidenced by the ATPase activity being localized in the myosin heads, which interact with actin microfilaments. Furthermore, as kinesin and myosin are both motor proteins that convert the chemical energy from ATP hydrolysis into mechanical work, their heads have likely preserved structural similarities essential for this function. By contrast, their tail regions, which mediate interactions with cargoes and other structural elements within the cell, have likely diverged more substantially to accommodate different cellular functions and structures.

This concept parallels the evolutionary relationship between FtsZ and tubulin, both of which are homologous structures. FtsZ, a prokaryotic origin protein, is considered the ancestral protein to both itself and tubulin, a eukaryotic protein. Despite their common ancestry, tubulin's function has evolved and diversified, especially in the context of cell-division machinery within multicellular eukaryotes.

When comparing proteins such as kinesin and myosin, it's the highly conserved nature of the ATPase activity within the heads that suggest their structural and functional homology. In contrast, the tails have evolved to fulfill specific roles within different cellular contexts, leading to greater structural divergence.