Teikyo University Medical School, Japan
Title: Direct Recording of Myosin head Power and Recovery Strokes in Hydrated Myosin Filaments Provides Evidence Against the Swinging Lever Arm Mechanism in Muscle Contraction
Biography: Haruo sugi
Muscle contraction results from relative sliding between actin and myosin filaments, which in turn is caused by cyclic attachment and detachment between myosin head extending from myosin filaments and active sites on actin filaments. A myosin head consists of catalytic (CAD), converter (COD), and lever arm (LD) domains, and connected to myosin filament backbone via subfragment-2. Based on crystallographic and electron microscopic studies on static structures of myosin heads and acto-myosin complex, it has been proposed that myosin head exerts power stroke by active rotation of CAD around CD, coupled with ATP hydrolysis. This mechanism is called “ swinging lever arm mechanism”, and now appears in every textbook as a dogma explaining molecular mechanism of muscle contraction. Using the gas environmental chamber, in which hydrated biomolecules can keep their function in the electron microscope, we succeeded in recording ATP-induced power and recovery strokes of myosin heads, which are position-marked with two different antibodies, attaching to junctional peptide between 50k and 20k segments of myosin heavy chain in CAD(antibody 1), and to reactive lysine residue in COD (antibody 2), respectively. Although antibody 1 covers two main myosin-binding sites on actin to inhibit formation of actin-myosin linkages, it has no effect on both Ca2+-activated muscle fiber contraction and in vitro actin-myosin sliding. On the other hand, antibody 2 shows no effect on muscle fiber contraction, but completely inhibits in vitro actin-myosin sliding. These findings, together with our success in recording power stroke of myosin heads position-marled with antibodies 1 and 2, constitute evidence against the dogma (or textbook view) that (1) during muscle contraction, myosin heads do not pass through rigor configuration, and (2) muscle contraction does not results from active rotation of CAD around COD.
Recent Publications :
- Sugi H et al. (1997) Dynamic electron microscopy of ATP-induced myosin head movement in living muscle thick filaments. Proc Natl Acad Sci USA 94: 4378―4382.
- Sugi H et al. (2008) Direct demonstration of the cross-bridge recovery stroke in muscle thick filaments in aqueous solution by using the hydration chamber. Proc. Natl. Acad. Sci. USA 105: 17396―17401.
- Sugi H et al. (2014) Definite differences between in vitro actin-myosin sliding and muscle contraction as revealed using antibodies to myosin head. PLoS ONE 9: e93272.
- Sugi H et al. (2015) Electron microscopic recording of myosin head power stroke in hydrated myosin filaments. Sci Rep 5: 15700.
- Sugi H, Chaen S (2016) Evidence against the swinging lever arm mechanism in muscle contraction based on the effect of antibodies to myosin head. J Nanomed Nanotechnol 7: 1000377.