Some properties of caldesmon and calponin and the participation of these proteins in regulation of smooth muscle contraction and cytoskeleton formation

The interaction of caldesmon with different Ca2+-binding proteins has been analyzed, and it is supposed that one of the conformers of calmodulin might be an endogenous regulator of caldesmon. The arrangement of caldesmon and Ca2+- binding proteins within their complexes has been analyzed by differen t methods. The central helix of calmodulin is Supposed to be located near t he single Cys residue in the C-terminal domain of caldesmon. The N-terminal globular domain of calmodulin interacts with sites A and B' of caldesmon, whereas the C-terminal globular domain of calmodulin binds to site B of cal desmon. The complex of calmodulin and caldesmon is very flexible; therefore , both parallel and antiparallel orientation of polypeptide chains of the t wo proteins is possible in experiments with short fragments of caldesmon an d calmodulin. The length, flexibility, and charge of the central helix of c almodulin play an important role in its interaction with caldesmon. Phospho rylation of caldesmon by different protein kinases in vitro has been analyz ed. It was shown that phosphorylation catalyzed by casein kinase II of site s located in the N-terminal domain decreases the interaction of caldesmon w ith myosin and tropomyosin. Caldesmon and calponin may interact with phosph olipids. The sites involved in the interaction of these actin-binding prote ins with phospholipids have been mapped. It is supposed that the interactio n of calponin and caldesmon with phospholipids may play a role in the forma tion of cytoskeleton. Calponin interacts with 90-kD heat shock protein (hsp 90) that may be involved in transportation of calponin and its proper inter action with different elements of cytoskeleton. Calponin, filamin, and (x-a ctinin can simultaneously interact with actin filaments. Simultaneous bindi ng of two actin-binding proteins affects the structure of actin bundles and their mechanical properties and may be of great importance in formation of different elements of cytoskeleton.