N-terminal polar amino acids of the C2 insert of nonmuscle myosin II-C2 regulate its functional properties.

In this study, we investigated the regions in the alternatively spliced C2 insert of nonmuscle myosin (NM) II-C conferring unique functional properties to the protein. We used constructs carrying deletions within different regions of C2 in neuronal cells; namely, the polar N terminus, the proline/serine-rich middle, and the nonpolar C terminus. We compared the wild-type NM II-C2 and deletion mutants with respect to ATPase activity, coassembly with NM II-B, regulation by myosin light-chain kinase (MLCK), and solubility, to determine the C2 region(s) involved in these processes. In addition, we examined the ability of the mutants to rescue the neurite-shortening phenotype upon NM II-C2 knockdown in Neuro-2a cells. Our data highlight the importance of the polar N terminus in NM II-C2 function.