The essential light chain is required for full force production by skeletal muscle myosin.
Myosin, a molecular motor that is responsible for muscle contraction, is composed of two heavy chains each with two light chains. The crystal structure of subfragment 1 indicates that both the regulatory light chains (RLCs) and the essential light chains (ELCs) stabilize an extended alpha-helical segment of the heavy chain. It has recently been shown in a motility assay that removal of either light chain markedly reduces actin filament sliding velocity without a significant loss in actin-activated ATPase activity. Here we demonstrate by single actin filament force measurements that RLC removal has little effect on isometric force, whereas ELC removal reduces isometric force by over 50%. These data are interpreted with a simple mechanical model where subfragment 1 behaves as a torque motor whose leyer arm length is sensitive to light-chain removal. Although the effect of removing RLCs fits within the confines of this model, altered crossbridge kinetics, as reflected in a reduced unloaded duty cycle, probably contributes to the reduced velocity and force production of ELC-deficient myosins.
VanBuren
P
P
Department of Molecular Physiology and Biophysics, University of Vermont, Burlington 05405.
Waller
G S
GS
Harris
D E
DE
Trybus
K M
KM
Warshaw
D M
DM
Lowey
S
S
D000199:Actins / Q000378:metabolism; D000205:Actomyosin / Q000378:metabolism*; D000818:Animals; D002645:Chickens; D066298:In Vitro Techniques; D009119:Muscle Contraction; D009218:Myosins / Q000378:metabolism / Q000502:physiology*
D000199:Actins; D000205:Actomyosin; D009218:Myosins