The structure of the rigor complex and its implications for the power stroke

• Published in: Philosophical transactions of the Royal Society of London. Series B. Biological sciences 2004-12, Vol.359 (1452), p.1819-1828
• Main Authors: Holmes, K. C., Trentham, D. R., Simmons, R., Schröder, R. R., Sweeney, H. L., Houdusse, Anne
• Format: Article
• Language: English
• Subjects: Actin; Actins; Actins - physiology; Animals; Arm; Biomechanical Phenomena; Coordinate systems; Cryo-Energy-Filter Electron Microscopy; Crystal structure; Decorated Actin; Electron microscopy; Microfilaments; Models, Biological; Models, Molecular; Muscle Contraction - physiology; Muscle, Skeletal - physiology; Myosin Cross-Bridge; Myosin V; Myosins - physiology; Nucleotides; Protein Conformation; Rotation; Smooth muscle; Strong Binding; Switches
• ISSN: 0962-8436; 1471-2970
• DOI: 10.1098/rstb.2004.1566

Decorated actin provides a model system for studying the strong interaction between actin and myosin. Cryo-energy-filter electron microscopy has recently yielded a 14 Å resolution map of rabbit skeletal actin decorated with chicken skeletal S1. The crystal structure of the cross-bridge from skeletal chicken myosin could not be fitted into the three-dimensional electron microscope map without some deformation. However, a newly published structure of the nucleotide-free myosin V cross-bridge, which is apparently already in the strong binding form, can be fitted into the three-dimensional reconstruction without distortion. This supports the notion that nucleotide-free myosin V is an excellent model for strongly bound myosin and allows us to describe the actin-myosin interface. In myosin V the switch 2 element is closed although the lever arm is down (post-power stroke). Therefore, it appears likely that switch 2 does not open very much during the power stroke. The myosin V structure also differs from the chicken skeletal myosin structure in the nucleotide-binding site and the degree of bending of the backbone ß-sheet. These suggest a mechanism for the control of the power stroke by strong actin binding.