Coevolution of head, neck, and tail domains of myosin heavy chains

Myosins, a large family of actin-based motors, have one or two heavy chains with one or more light chains associated with each heavy chain. The heavy chains have a (generally) N-terminal head domain with an ATPase and actin-b inding site, followed by a neck domain to which the light chains bind, and a C-terminal tail domain through which the heavy chains self-associate and/ or bind the myosin to its cargo. Approximately 140 members of the myosin su perfamily have been grouped into 17 classes based on the sequences of their head domains. I now show that a phylogenetic tree based on the sequences o f the combined neck and tail domains groups 144 myosins, with a few excepti ons, into the same 17 classes. For the nine myosin classes that have multip le members, phylogenetic trees based on the head domain or the combined nec k/tail domains are either identical or very similar. For class II myosins. very similar phylogenetic: trees are obtained for the head, neck, and tail domains of 47 heavy chains and for 29 essential light chains and 19 regulat ory light chains. These data strongly suggest that the head, neck, and tail domains of all myosin heavy chains. and light chains at least of class II myosins, have coevolved and are likely to be functionally interdependent, c onsistent with biochemical evidence showing that regulated actin-dependent MgATPase activity of Dictyostelium myosin II requires isoform specific inte ractions between the heavy chain head and tail and light chains.