A large and distinct rotation of the myosin light chain domain occurs upon muscle contraction

A large and distinct rotation of the myosin light chain domain occurs upon muscle contraction

Department of Biochemistry, University of Minnesota Medical School, Minneapolis, MN 55455

Edited by Thomas D. Pollard, Salk Institute for Biological Studies, La Jolla, CA, and approved January 2, 1998 (received for review November 3, 1997)

Abstract

For more than 30 years, the fundamental goal in molecular motility has been to resolve force-generating motor protein structural changes. Although low-resolution structural studies have provided evidence for force-generating myosin rotations upon muscle activation, these studies did not resolve structural states of myosin in contracting muscle. Using electron paramagnetic resonance, we observed two distinct orientations of a spin label attached specifically to a single site on the light chain domain of myosin in relaxed scallop muscle fibers. The two probe orientations, separated by a 36° ± 5° axial rotation, did not change upon muscle activation, but the distribution between them changed substantially, indicating that a fraction (17% ± 2%) of myosin heads undergoes a large (at least 30°) axial rotation of the myosin light chain domain upon force generation and muscle contraction. The resulting model helps explain why this observation has remained so elusive and provides insight into the mechanisms by which motor protein structural transitions drive molecular motility.

Footnotes

↵ * J.E.B. and I.B.-M. contributed equally to this work.
↵ † To whom reprint requests should be addressed. e-mail: ddt{at}ddt.biochem.umn.edu.
This paper was submitted directly (Track II) to the Proceedings Office.
Abbreviations: EPR, electron paramagnetic resonance; FDNASL, 3-(5-fluoro-2,4-dinitroanilino)-2,2,5,5-tetramethyl-1-pyrrolidinyloxy; LC, light chain; RLC, regulatory LC.
A commentary on this article begins on page 2720.