This Article Full Text Full Text (PDF) All Versions of this Article: biophysj.106.095802v1 93/6/2083    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Espinoza-Fonseca, L. M. Articles by Thomas, D. D. Search for Related Content PubMed PubMed Citation Articles by Espinoza-Fonseca, L. M. Articles by Thomas, D. D.

Molecular Dynamics Simulations Reveal a Disorder-to-Order Transition on Phosphorylation of Smooth Muscle Myosin

Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455

Correspondence: Address reprint requests to David D. Thomas, Dept. of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455. E-mail: ddt{at}umn.edu.

We have performed molecular dynamics simulations of the phosphorylated (at S-19) and the unphosphorylated 25-residue N-terminal phosphorylation domain of the regulatory light chain (RLC) of smooth muscle myosin to provide insight into the structural basis of regulation. This domain does not appear in any crystal structure, so these simulations were combined with site-directed spin labeling to define its structure and dynamics. Simulations were carried out in explicit water at 310 K, starting with an ideal -helix. In the absence of phosphorylation, large portions of the domain (residues S-2 to K-11 and R-16 through Y-21) were metastable throughout the simulation, undergoing rapid transitions among -helix, -helix, and turn, whereas residues K-12 to Q-15 remained highly disordered, displaying a turn motif from 1 to 22.5 ns and a random coil pattern from 22.5 to 50 ns. Phosphorylation increased -helical order dramatically in residues K-11 to A-17 but caused relatively little change in the immediate vicinity of the phosphorylation site (S-19). Phosphorylation also increased the overall dynamic stability, as evidenced by smaller temporal fluctuations in the root mean-square deviation. These results on the isolated phosphorylation domain, predicting a disorder-to-order transition induced by phosphorylation, are remarkably consistent with published experimental data involving site-directed spin labeling of the intact RLC bound to the two-headed heavy meromyosin. The simulations provide new insight into structural details not revealed by experiment, allowing us to propose a refined model for the mechanism by which phosphorylation affects the N-terminal domain of the RLC of smooth muscle myosin.