Table 2. The complex salt bridge and kinetic coupling.
| Myosin isoforms | Amino acid at position 177 | Amino acid at position 236 | Amino acid at position 675 | Interactions observed in crystal structure among residues in the three positions (ref.) | Coupling* between ADP/actin affinity KDA/KA = KAD/KD (ref.) |
|---|---|---|---|---|---|
| Scallop (Argopecten irradians) striated muscle | E(177) | R(236) | E(675) | Complex salt bridge (this work) | 45-48 (17) |
| Rabbit skeletal muscle | E(180) | R(240) | E(680) | Complex salt bridge (chicken skeletal muscle S1) (16) | 100 (17) 30-60 (49) |
| Drosophila indirect flight muscle | E(180) | R(237) | E(678) | NA | 55 (38) |
| Drosophila embryonic muscle | E(180) | R(236) | E(678) | NA | 300 (38) |
| Bovine cardiac (α/β) muscle | E(179) | R(237) | E(677) | NA | 15-20 (50) |
| Chicken gizzard smooth muscle | E(177) | K(240) | H(688) | Weak single salt bridge (1BR1, 1BR4) (8) | 4 (18) |
Residues involved in the complex salt bridge or their sequence equivalents from several muscle myosins and the kinetic coupling in the respective isoform. NA, not available.
*
The coupling is given by the ratio of the actin dissociation constant from myosin in the presence and absence of ADP (KDA/KA) or the ADP dissociation constant from myosin in the presence and absence of actin (KAD/KD).