Structural investigations on the role of microfilaments in ligand translocation

This chapter discusses the role of microfilaments in ligand translocation. Translocation of ligand-receptor clusters at the cell surface and of ligand-laden vesicles within the cell occurs in a rapid and directed fashion. Evidence implicating a role for actin-based cortical microfilaments in ligand translocation is accumulating. Nonmuscle cells contain actin and myosin and these proteins form functional hybrid complexes with their muscle counterparts that are capable of tension development and contraction in vitro. These properties of the nonmuscle cytoskeleton suggest that the essential functional domains of contractile proteins such as actin and myosin are highly conserved and can be utilized by nonmuscle cells for movement. A wide variety of actin-binding proteins occur in muscle and nonmuscle cells that nucleate, cross-link, or cap actin filaments and thereby play a fundamental role in regulating microfilament polarity, length, and specific association with other structural elements of the cytoplasm.