{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Caldesmon is a calmodulin-binding protein that regulates the interaction of actin and myosin in smooth muscle. Caldesmon inhibits the actinomyosin ATPase that regulates actin/myosin cross-bridge cycling and contraction. Unphosphorylated caldesmon binds tightly to the actin filament exerting this inhibition, but when caldesmon is phosphorylated, the binding is diminished and actinomyosin ATPase activity increases, augmenting contraction. In addition to its role in smooth muscle contraction, caldesmon is involved in regulating cell motility and cytoskeletal dynamics in non-muscle cells. It interacts with actin filaments and microtubules, contributing to the organization of the cytoskeleton and cell shape. Caldesmon also participates in cell adhesion and migration processes, which are important for tissue remodeling, wound healing, and metastasis. Two closely-related variants of human caldesmon have been identified. The h-caldesmon variant (120–150 kD) is predominantly expressed in smooth muscle, whereas I-caldesmon (70–80 kD) is found in non-muscle tissue and cells. Anti-caldesmon recognizes only the h-caldesmon variant, and labels smooth muscle and tumors of smooth muscle, myofibroblastic, and myoepithelial differentiation."}]}]}