Role of caldesmon in the thin filament

Ultrastructural studies of isolated chicken gizzard thin filaments localized caldesmon on the thin filament beside tropomyosin, arranged continuously along the axis of the actin double helix (Moody et al 1990, Vibert et al 1993, I hman et al 1997). In smooth muscle filaments derived from vascular or visceral tissue, the stoichiometry of caldesmon to tropomyosin and actin has been determined to be 1 2 14 (Lehman et al 1989, Marston 1990, Lehman et al 1993). Marston and Redwood (1991) proposed that each caldesmon molecule is placed in register with tropomyosin and extends for 78 nm, the length of two tropomyosin molecules. Each caldesmon molecule interacts with 14 actin monomers. This would result in a filament without radial symmetry such that different parts of the caldesmon molecule would appear on the same side of the actin filament. 

the physiologic role of caldesmon binding to myosin is presently uncertain. 

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