Alternative relay regulates the adenosine triphosphatase activity of Locusta migratoria striated muscle myosin

Abstract Locust ( Locusta migratoria ) has a single striated muscle myosin heavy chain ( Mhc ) gene, which contains 5 clusters of alternative exclusive exons and 1 differently included penultimate exon. The alternative exons of Mhc gene encode 4 distinct regions in the myosin motor domain, that is, the N‐terminal SH3‐like domain, one lip of the nucleotide‐binding pocket, the relay, and the converter. Here, we investigated the role of the alternative regions on the motor function of locust muscle myosin. Using Sf9‐baculovirus protein expression system, we expressed and purified 5 isoforms of the locust muscle myosin heavy meromyosin (HMM), including the major isoform in the thorax dorsal longitudinal flight muscle (FL1) and 4 isoforms expressed in the abdominal intersegmental muscle (AB1 to AB4). Among these 5 HMMs, FL1‐HMM displayed the highest level of actin‐activated adenosine triphosphatase (ATPase) activity (hereafter referred as ATPase activity). To identify the alternative region(s) responsible for the elevated ATPase activity of FL1‐HMM, we produced a number of chimeras of FL1‐HMM and AB4‐HMM. Substitution with the relay of AB4‐HMM (encoded by exon‐14c) substantially decreased the ATPase activity of FL1‐HMM, and conversely, the relay of FL1‐HMM (encoded by exon‐14a) enhanced the ATPase activity of AB4‐HMM. Mutagenesis showed that the exon‐14a‐encoded residues Gly 474 and Asn 509 are responsible for the elevated ATPase activity of FL1‐HMM. Those results indicate that the alternative relay encoded by exon‐14a/c play a key role in regulating the ATPase activity of FL1‐HMM and AB4‐HMM.