Full-length rat alpha and beta cardiac myosin heavy chain sequences. Comparisons suggest a molecular basis for functional differences

The two cardiac myosin heavy chain isoforms, α and β, differ functionally. α Myosin exhibits higher actin-activated ATPase than does β myosin, and hearts expressing α myosin exhibit increased contractility relative to hearts expressing β myosin. To understand the molecular basis for this functional difference, we determined the complete nucleotide sequence of full-length rat α and β myosin heavy chain cDNAs. This study represents the first opportunity to compare full-length fast ATPase and slow ATPase muscle myosin sequences. The α and β myosin heavy chain amino acid sequences are more related to each other than to other sarcomeric myosin heavy chain sequences. Of the 1938 amino acid residues in α and β myosin heavy chain, 131 are non-identical with 37 non-conservative changes. Two-thirds of these non-identical residues are clustered, and several of these clusters map to regions that have been implicated as functionally important. Some of the regions identified by the clusters of non-identical amino acid residues may affect actin binding, ATP hydrolysis and force production.