In-register homodimers of smooth muscle tropomyosin.
Gizzard smooth muscle tropomyosin dimer molecules were dissociated by guanidinium chloride and reassociated by dialysis against 1 M NaCl. Several properties of the protein were changed by this treatment. There was a large decrease in tropomyosin's low-salt viscosity, owing to reduced end-to-end polymerization, the helix unfolding profile changed from a one-step to a two-step process, and the ability to form intramolecular, interchain, disulfide-cross-linked homodimers increased dramatically. Thus, the native molecule, though to exist predominantly as by the beta gamma heterodimer which cannot form disulfide cross-links [Sanders, C., Burtnick, L.D., & Smillie, L. B. (1986) J. Biol. Chem. 261, 12774-12778], reassembles, after dissociation, to form predominantly parallel, in-register beta beta and gamma gamma homodimers able to form disulfide cross-links. This suggests that the physical properties, including the end-to-end interaction, of gizzard tropomyosin homodimers differ considerably from those of the heterodimer. This is a first step toward a molecular understanding of the end-to-end interaction of smooth muscle tropomyosin.
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Department of Muscle Research, Boston Biomedical Research Institute, Massachusetts 02114.
D000818:Animals; D002645:Chickens; D004220:Disulfides; D005895:Gizzard, Avian; D019791:Guanidine; D006146:Guanidines; D046911:Macromolecular Substances; D009130:Muscle, Smooth / Q000378:metabolism*; D009994:Osmolar Concentration; D013816:Thermodynamics; D014335:Tropomyosin / Q000378:metabolism*; D014783:Viscosity
D004220:Disulfides; D006146:Guanidines; D046911:Macromolecular Substances; D014335:Tropomyosin; D019791:Guanidine