Interactions between G-actin and myosin subfragment 1: immunochemical probing of the NH2-terminal segment on actin.
The role of the N-terminal segment of actin in myosin-induced polymerization of G-actin was studied by using peptide antibodies directed against the first seven N-terminal residues of alpha-skeletal actin. Light scattering, fluorescence, and analytical ultracentrifugation experiments showed that the Fab fragments of these antibodies inhibited the polymerization of G-actin by myosin subfragment 1 (S-1) by inhibiting the binding of these proteins to each other. Fluorescence measurements using actin labeled with pyrenyliodoacetamide revealed that Fab inhibited the initial step in the binding of S-1 to G-actin. It is deduced from these results and from other literature data that the initial contact between G-actin and S-1 involves residues 1-7 on actin and residues 633-642 on the S-1 heavy chain. This interaction appears to be of major importance for the binding of S-1 and G-actin. The presence of additional myosin contact sites on G-actin was indicated by concentration-dependent recovery of S-1 binding to G-actin without displacement of Fab. The reduced Fab inhibition of S-1 binding to polymerizing and polymerized actin is consistent with the tightening of acto-S-1 binding at these sites or the creation of new sites upon formation of F-actin.
DasGupta
G
G
Molecular Biology Institute, University of California, Los Angeles 90024.
White
J
J
Cheung
P
P
Reisler
E
E
D000199:Actins / Q000276:immunology / Q000378:metabolism*; D000906:Antibodies / Q000378:metabolism; D005456:Fluorescent Dyes; D007140:Immunoglobulin Fab Fragments / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D010446:Peptide Fragments / Q000276:immunology / Q000378:metabolism*; D011485:Protein Binding; D014461:Ultracentrifugation
D000199:Actins; D000906:Antibodies; D005456:Fluorescent Dyes; D007140:Immunoglobulin Fab Fragments; D010446:Peptide Fragments; D009218:Myosins