Roles of the amino acid side chains in the actin-binding S-site of myosin heavy chain.
The heptapeptide Ile-Arg-Ile-Cys-Arg-Lys-Gly-OEt is the analog of the S-site, one of the actin-binding sites in myosin [Suzuki et al. (1987) J. Biol. Chem. 262, 11410-11412]. Various substituted heptapeptides were synthesized, and the dissociation constants of each acto-heptapeptide complex was measured. Comparison of the dissociation constants indicated that the hydrophobic side chain of Ile-1 was critical for the binding with F-actin, but not that of Ile-3. The positive charge and the side chain length of Arg-2 were also important. The presence of a sulfur atom in the Cys-4 was also necessary. The affinity of the N-terminal Ile-Arg-Ile part for F-actin was influenced by the kind of residues in the C-terminal tetrapeptide part. Based on these results, the side chains of Ile(702), Arg(703), and Cys(SH1)(705) in myosin subfragment-1 heavy chain were assigned to be critical for the binding with F-actin. The amino acid sequence of S-1 heavy chain containing these critical residues for the S-site from residue number 700 to 717 can be predicted as an analogue of the segment B of the ATP-binding site [Walker et al. (1982) EMBO J. 1, 945-951]. The actin-binding S-site possibly shares a part of the ATP-binding site in myosin. We discuss the possibility that the S-site is an inhibitory site of myosin ATPase and the so-called actin-activation of myosin ATPase is a deinhibition induced by transient binding of F-actin to the S-site.
Eto
M
M
Department of Chemistry, Faculty of Science, Hokkaido University.
Suzuki
R
R
Morita
F
F
Kuwayama
H
H
Nishi
N
N
Tokura
S
S
D000199:Actins / Q000378:metabolism*; D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D004789:Enzyme Activation; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009132:Muscles / Q000737:chemistry; D009218:Myosins / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D011817:Rabbits
D000199:Actins; D000251:Adenosine Triphosphatases; D009218:Myosins