Characterization of myosin heavy chains from the mantle muscles of cephalopods

Myosin heavy chain (MyHC) genes from the mantle muscles of three cephalopod species, namely, golden cuttlefish Sepia esculenta, Japanese common squid Todarodes pacificus, and spear squid Loligo bleekeri were subjected to synthesis of first strand cDNA by reverse transcription-PCR. As a result of sequencing of the obtained cDNA fragments, the MyHCs from S. esculenta and L. bleekeri were found to consist of 1936 amino acids, while T. pacificus MyHC consisted of 1939 residues. The sequences were found to be 73%, 55%, and 41% identical to those of the Ca2+-regulated scallop MyHCs, human skeletal MyHC, and chicken gizzard (smooth muscle) MyHC, respectively. The cephalopod MyHCs conserved ATPand actin-binding sites as well as light chain binding sites in the head (S1) region with the clear differences in sequence homology from those of higher organisms, and typical α-helical heptad repeats involved in the formation of coiled-coil structure in the rod region. The sequences of the two surface loops at the 25/50 kDa and 50/20 kDa junctions of the motor domain were found to be conserved among cephalopods compared to those from the other sources. In the phylogenetic tree based on the amino acid sequences, the cephalopod MyHCs formed a cluster, clearly different from the other invertebrate counterparts, in accordance with the results of tertiary structure modeling of the head regions.