Harmonized supramolecular motility machinery and its diversity

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Movement of Actin-associated Myosin-II (Cross-Bridge) during Muscle Contraction

Species name:Rabbit

Osaka City Univ　Eisaku KATAYAMA

The first part of the movie indicates the movement of individual myosin-head (crossbridge), based on conventional "Tilting-Leverarm Hypothesis". Such movement was proposed from the characteristic features of the atomic models of myosin-S1 in the absence and the presence of ATP, together with the well-known experimental evidence that "the motor-domain does not appreciably rotate during the Power-Stroke". Hence, this hypothesis claims that the Power-Stroke is essentially the transition between strongly actin-bound rigor-structure (1DFK: lever-arm is extended) and ATP-bound kinked structure (1DFL). If the motor-domain is immobilized on actin, the lever-arm moiety should swing along the actin filament, The latter half of the movie exhibits the revised crossbridge-cycle we have proposed according to our direct observation of in vitro sliding actomyosin by Quick-Freeze Deep-Etch Replica Electron Microscopy (Ref. 1, 2). We noticed that the actual images of actin-sliding myosin cannot be explained by the conventional hypothesis as above, suggesting the presence of a new conformer whose crystal structure is not yet reported. After extensive search, we finally found that SH1-SH2 crosslinked myosin could be a good candidate of the new conformer whose lever-arm bends to the opposite side of ATP-bound kinked structure (Ref.3-5). Since we could successfully reconstruct its low-resolution 3-D model by a new version of single-particle-analysis (Ref. 5). Taking the results of time-resolved chemical crosslinking into consideration, we revised the scheme of crossbridge-cycle including the new conformer (Ref.5). .The conformational change shown in the movie is compatible with all the images we actually observed under in vitro actin-sliding conditions. [References] 1. Katayama E. The effects of various nucleotides on the structure of actin-attached myosin subfragment-1 studied by quick-freeze deep-etch electron microscopy. J Biochem. 1989 Nov;106(5):751-70. 2: Katayama E. Quick-freeze deep-etch electron microscopy of the actin-heavy meromyosin complex during the in vitro motility assay. J Mol Biol. 1998 May 1;278(2):349-67. 3: Katayama E, Ohmori G, Baba N. Three-dimensional image analysis of myosin head in function as captured by quick-freeze deep-etch replica electron microscopy. Adv Exp Med Biol. 1998;453:37-45. 4: Katayama E, Ichise N, Yaeguchi N, Yoshizawa T, Maruta S, Baba N. Three-dimensional structural analysis of individual myosin heads under various functional states. Adv Exp Med Biol. 2003;538:295-304. 5: Kimori Y, Baba N, Katayama E. Novel configuration of a myosin II transient intermediate analogue revealed by quick-freeze deep-etch replica electron microscopy. Biochem J. 2013 Feb 15;450(1):23-35. 6. Andreev OA, Reshetnyak YK. Mechanism of formation of actomyosin interface. J Mol Biol. 2007 Jan 19;365(3):551-4.