High Pressure Adaptation of Muscle Proteins from Deep-Sea Fish

Deep-sea fish distributes to abyssal depths of several thousand meters, the pressures of which shallower-living fish cannot tolerate. Tolerance to abyssal pressures by deep-sea fish is likely to depend at least in part on adaptive modifications of proteins. However, structural modifications that allow proteins to function at high pressures have not been well understood. To elucidate the mechanisms of protein adaptation to high pressures, we cloned α-actin and myosin heavy chain cDNAs 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 comparison of the α-actins from deep-sea fishes with those of non deep-sea fishes identified three amino acid substitutions, which would make the deep-sea fish actin function even at 60 MPa. The myosin heavy chains from deep-sea fishes have a Pro residue in the loop-1 region and have a shorter loop-2 region than non deep-sea fishes. Additionally, the myosin heavy chains from deep-sea fishes have the biased amino acid substitutions at core positions in the coiled-coil structure of the rod region. The roles of these characteristic sequences in myosin heavy chain from deep-sea fish, however, have remained unclear.