High‐pressure adaptation of muscle proteins from deep‐sea fishes, Coryphaenoides yaquinae and C. armatus

The evolutionary adaptations of functional genes to life at high pressures are not well understood. To elucidate the mechanisms of protein adaptation to high pressures, we isolated two muscle protein‐encoding cDNAs, α‐actin and myosin heavy chain (MyHC), derived from skeletal muscles of two deep‐sea fishes, Coryphaenoides yaquinae and C. armatus , and two non‐deep‐sea fishes, C. acrolepis and C. cinereus . The α‐actins from two deep‐sea fishes have three amino acid substitutions in comparison to those of non‐deep‐sea fishes. These substitutions enable the deep‐sea fish actins to function even at 60 MPa. The MyHCs of the two deep‐sea fishes have a proline residue in the loop‐1 region and have a shorter loop‐2 region than the non‐deep‐sea fishes. Additionally, the MyHCs of deep‐sea fishes have biased amino acid substitutions at core positions within the coiled‐coil structure of the rod region. The roles of these substitutions in the deep‐sea fishes MyHCs, however, remain unclear.