Binding of the amino-terminal region of myosin alkali 1 light chain to actin and its effect on actin-myosin interaction.

The role of the amino-terminal region of myosin alkali 1 light chain (A1) in the interaction between actin and myosin subfragment-1 (S-1) was explored. Papain digestion of skeletal myosin filaments produced S-1 whose A1 was found to lose the basic 13 amino-terminal amino acid residues (A1'). We obtained three types of papain S-1 isoenzymes differing in their alkali light chain content: recombined papain S-1 (A1), papain S-1 (A1'), and papain S-1 (A2). Both the maximum turnover rate (Vmax) and the dissociation constant (Km) for actin-activated papain S-1 (A1') ATPase activity were similar to those for papain S-1 (A2) and remarkably larger than those for recombined papain S-1 (A1). The 13 amino-terminal residue peptide of A1 (N-pep) was isolated and characterized. 1H-NMR spectroscopy suggested that the N-pep was relatively immobilized in the presence of actin filaments. A cross-linking study suggested that N-pep binds to actin. The addition of N-pep to acto-S-1 (A1) made Km and Vmax for the actin-activated ATPase activity close to those for S-1 (A2). Removal of the trimethyl group from the N-pep suppressed the above effect on the actin-S-1 interaction. Our findings suggest that the amino-terminal region of A1 binds to the actin molecule to affect the mechanism of actin-activated S-1 ATPase.