| Actin is a key component of the cytoskeleton and contractile apparatus of many eukaryotic cells. The actin concentration of cells is relatively constant and the pool of actin must be remodeled as the needs of the cell demand. G-actin is a globular protein of about 42,000 Mr. Under physiological conditions, actin forms a helical polymer. Polymerized actin or F-actin can assume a variety of forms in cells ranging from single filaments to parallel bundles of filaments to complex branched networks. Each form of actin has its own cellular function.; Changes in the actin network are brought about by a large number of actin binding proteins. A recent addition to this list of proteins is the protein fesselin discovered in our laboratory a few short years ago. Fesselin has dramatic effects on actin polymerization and actin filament organization, thus, making this protein a potentially important part of the actin cytoskeleton of smooth muscle. Fesselin is also localized along the actin filaments in the contractile domain of skeletal muscle, possibly regulating either the length of the sarcomere or the interaction between actin and regulatory proteins of the contractile domain. Fesselin shares regions of sequence of homology with synaptopodin, an actin binding protein found in mouse brain and kidney, and another actin binding protein, myopodin, which is found in both smooth and skeletal muscle. It is thought that fesselin may exist as another member of the synaptopodin gene family. |
