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Unformatted text preview: 14-1Cell and Molecular Biology (Biol. Chem. 410A)Lecture #14Harry R. Matthews, Ph.D.October 15, 1996Muscle and Other Molecular MotorsLearning objectives:• Myosin structure and function• Regulation of muscle contraction in smooth muscle• Regulation of muscle contraction in skeletal muscle• Directed intracellular transport• Kinesin and DyneinOptional reading:•Stryer IV: Chapter 15. Lodish et al., Ch. 23.roteins provide both the motive force and the regulation of muscle move-ment. Although the motive force is provided by sliding filaments in all muscle, the regulation differs between smooth muscle and skeletal muscle.PMuscleActin, together with proteins tropomyosin and troponin, forms the thin filaments of muscle cells. In muscle cells, thin filaments are interspersed longitudinally with thick fila-ments, made from myosin. Myosin is a large protein containing two identical heavy chains. Each heavy chain has a long straight α-helical domain and one glob-ular domain. In myosin, the two α-helical do-mains form a parallel coiled-coil structure with the two globular domains at one end. Myosin additionally contains two each of two kinds of light chain which are bound to the globular domains of the heavy chains. These myosin molecules aggregate specifically to form the thick filaments. The actin in the thin filaments binds myosin to produce a complex of actin and myosin called actomyosin. Hydrolysis of ATP by myos-in causes conformational changes in the glob-ular domains of the heavy chains leading to sliding of the thick filaments past the thin fil-aments, contracting the muscle. The nature of the conformational changes is beginning to be understood with the determ-ination of 3-dimensional structures for actin and the globular domain of myosin. The globu-lar domain of myosin, also called the “head” or “myosin S1”, forms two subdomains. One of these contains the ATP binding site and the actin binding site; the other is a long rod formed by an α-helix which is part of the heavy chain protected by the light chains. The rod subdomain acts as a lever joining the...
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- Spring '03