Myosin II from rabbit skeletal muscle and Dictyostelium discoideum and its interaction with F‐actin studied by ¹H NMR spectroscopy

Abstract

Mg-F-actin occurs in two conformational states, I and M, where the N-terminal amino acids are either immobile or highly mobile. In the rigor or ADP complex of rabbit myosin S1 with Mg-F-actin the N-terminal acetyl group of actin stays in its highly mobile state. The same is true for the complexes with the myosin motor domain from Dictyostelium discoideum. This excludes a direct strong interaction of the N-terminal amino acids with myosin in the rigor state as suggested. An interaction of the N-terminus of F-actin with myosin is also not promoted by occupying its low-affinity binding site(s) with divalent ions. The N-terminal high-mobility region may be part of a structural system which has evolved for releasing inadequate stress applied to the actin filaments ß 2002 Published by Elsevier Science B.V. on behalf of the Federation of European Biochemical Societies.

Myosin isoforms show unique conformations in the actin-bound state

“…However, a region of significant structural flexibility remains close to the N terminus of actin in subdomain 1 (D1) in all of the actomyosin reconstructions. This result is supported by a recent NMR study that also shows flexibility at actin's N terminus in both strongly bound states of skeletal actomyosin (27). There is a significant discrepancy peak between subdomain 2 (D2) of the lower actin and the C terminus of the upper actin in both the skeletal and smooth-muscle isoforms.…”

All-Atom Molecular Dynamics Simulations of Actin–Myosin Interactions: A Comparative Study of Cardiac α Myosin, β Myosin, and Fast Skeletal Muscle Myosin

“…On the other hand, we should also consider the restraining effect of the rest of F-actin on the three actin subunits (AC1–AC3) included in our MD simulations. Therefore, to properly control the flexibility of AC1–AC3 in our MD simulations, we have imposed weak positional restraints (using harmonic springs with a force constant of 0.01 kcal mol –1 Å –2 ) on the Cα atoms of actin residues excluding the highly flexible N-terminal residues 1–4. , To calibrate the actin flexibility entailed by such restraints, we have calculated the average rmsd for AC1–AC3 (relative to the initial models) during the last 2 ns of all MD trajectories, which yield rmsd values of 1.8–2.1 Å (see Table S3 of the Supporting Information). For comparison, we have calculated the rmsd between the flexibly fitted actin models obtained in two EM-fitting studies , and the initial actin models [PDB entries and (see refs and )], which gave similar rmsd values of 1.9–2.2 Å. Additionally, the rmsd between two recent actin models (PDB entries and ) is also 2 Å.…”