Title

Millisecond time-resolved changes occurring in Ca2+-regulated myosin filaments upon relaxation

UMMS Affiliation

Department of Cell Biology

Date

7-1-2008

Document Type

Article

Subjects

Animals; Calcium; Cryoelectron Microscopy; Kinetics; Microfilaments; Mollusca; Myosins; Time Factors

Disciplines

Life Sciences | Medicine and Health Sciences

Abstract

Contraction of many muscles is activated in part by the binding of Ca(2+) to, or phosphorylation of, the myosin heads on the surface of the thick filaments. In relaxed muscle, the myosin heads are helically ordered and undergo minimal interaction with actin. On Ca(2+) binding or phosphorylation, the head array becomes disordered, reflecting breakage of the head-head and other interactions that underlie the ordered structure. Loosening of the heads from the filament surface enables them to interact with actin filaments, bringing about contraction. On relaxation, the heads return to their ordered positions on the filament backbone. In scallop striated adductor muscle, the disordering that takes place on Ca(2+) binding occurs on the millisecond time scale, suggesting that it is a key element of muscle activation. Here we have studied the reverse process. Using time-resolved negative staining electron microscopy, we show that the rate of reordering on removal of Ca(2+) also occurs on the same physiological time scale. Direct observation of images together with analysis of their Fourier transforms shows that activated heads regain their axial ordering within 20 ms and become ordered in their final helical positions within 50 ms. This rapid reordering suggests that reformation of the ordered structure, and the head-head and other interactions that underlie it, is a critical element of the relaxation process.

Rights and Permissions

Citation: J Mol Biol. 2008 Aug 29;381(2):256-60. Epub 2008 Jun 18. Link to article on publisher's site

DOI of Published Version

10.1016/j.jmb.2008.06.032

Related Resources

Link to Article in PubMed

Journal Title

Journal of molecular biology

PubMed ID

18585394