The structure of the rigor complex and its implications for the power stroke.
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 A 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 beta-sheet. These suggest a mechanism for the control of the power stroke by strong actin binding.
Holmes
K C
KC
Max Planck Institute for Medical Research, 69120 Heidelberg, Germany. holmes@mpimf-heidelberg.mpg.de
Schröder
R R
RR
Sweeney
H L
HL
Houdusse
Anne
A
D000199:Actins / Q000502:physiology*; D000818:Animals; D001696:Biomechanical Phenomena; D008954:Models, Biological; D008958:Models, Molecular; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D009218:Myosins / Q000502:physiology*; D011487:Protein Conformation
D000199:Actins; D009218:Myosins