Biochemical and Functional Characterization of Smooth Muscle Calponin
Calponin (calcium- and calmodulin-binding troponin T-like protein) was first described by Takahashi et al. (1986) and isolated from chicken gizzard smooth muscle taking advantage of its heat-stability. The isolated protein was shown to bind calmodulin (by affinity chromatography) in a Ca2+-dependent manner, and F-actin or F-actin-tropomyosin (by analytical ultracentrifugation) in a Ca2+-independent manner. Its tissue content was estimated to be equi-molar to tropomyosin. These properties suggested that calponin may be a thin filament-associated protein involved in regulating the contractile state of smooth muscle. This notion was supported by our analysis of thin filament preparations from chicken gizzard which were designed to retain actin-binding protein components (Ngai et al., 1987). Such thin filament preparations (cf. Marston and Lehman, 1985) contain, in addition to actin and tropomyosin, caldesmon (140 kDa) and a 32 kDa protein later shown to be identical to calponin (Fig. 1 right-hand panel). This figure also shows the calponin in gizzard actomyosin preparations (left-hand panel).
KeywordsThin Filament Myosin Light Chain Kinase Actin Monomer Smooth Muscle Myosin Actomyosin ATPase
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