The study demonstrates that the N-terminal amino acids of F-actin do not have a direct strong interaction with myosin in the rigor state, suggesting this region may act to release inadequate stress on actin filaments.
Challenges models of direct N-terminal actin-myosin contacts in rigor; leaves open its role in actin filament stress release.
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.
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Kany et al. (2002) studied this question.
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