Key result
Calcium and tropomyosin activate MgATP hydrolysis and motility of vertebrate non-skeletal muscle myosin II proteins, but inhibit vertebrate brush border myosin I.
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Differentiates myosin isoform regulation; extends cytoskeletal biology but leaves open in vivo and clinical translation.
Cell motility events require movement of the cytoskeleton. Actin-based movement is catalyzed by the mechanoenzyme myosin, which translocates toward the barbed end of actin filaments in an ATP-dependent fashion. There are two subclasses of myosin with different structures and functions: conventional filamentous myosin (myosin II) and monomeric myosin I. Vertebrate non-muscle myosins I and II function as similar actin motors in vitro, catalyzing virtually identical actin-activated MgATP hydrolysis and motility. The functional diversification of these two enzymes results from their differential regulation. Calcium and tropomyosin, which activate the MgATP hydrolysis and motility of vertebrate non-skeletal muscle myosin II proteins, inhibit vertebrate (brush border) myosin I. The activities and regulation of brush border myosin I provide insight into conserved and unique features of the myosin mechanoenzymes and suggest how the functions of myosins I and II are divided in vertebrate cells. Brush border myosin I as an enzyme also contributes to our understanding of the molecular mechanism of motility.
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Collins et al. (1991) studied this question. Calcium and tropomyosin activate MgATP hydrolysis and motility of vertebrate non-skeletal muscle myosin II proteins, but inhibit vertebrate brush border myosin I.
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