PRIMARY STRUCTURE OF THE HINGE REGION IN ADULT CHICKEN CARDIAC MYOSIN SUBFRAGMENT-2

The complete amino-acid sequence of the hinge region in the subfragment-2 (S-2) derived from adult chicken cardiac ventricular muscle myosin has been determined by direct protein sequencing. The entire amino-acid sequence of this hinge composed of 143 residues was established by structural analysis of CNBr peptides, lysyl and arginyl endopeptidase peptides of carboxymethylated S-2. By sequence comparison with the corresponding region of the same chicken cardiac myosin which was recently deduced from its cDNA eight amino-acid differences were recognized. Comparing the sequence of this hinge with those of other cardiac myosins such as rat alpha- and beta-myosin heavy chains (MHC), rabbit alpha-MHC and human alpha- and beta-MHCs relatively lower degrees of sequence identities, namely 74.8%, 77.6%, 76.1% 75.5% and 75.5%, are observed. On the other hand, more than 89.5% sequence identities are shown among these mammalian cardiac myosins. These results indicate that avian cardiac MHC has diverged earlier than mammalian cardiac myosin has diverged to alpha- and beta-MHC. Amino-acid substitutions in this hinge region form a cluster on the C-terminal sequence region. On the contrary, in the N-terminal portion, completely conserved segments are observed, suggesting that these regions may contribute to the myosin ATPase activity and muscle contraction.