Biochemistry of actomyosin-dependent cell motility (a review).

Abstract

Actins akd myosins similar to the major proteins of muscle are the major molecular components of intricate mechanochemical systems that perform numerous vital motility and structural functions in all eukaryotic cells. In this article, after a brief summary of the morphological distribution and ultrastructure of actin, myosin, and interrelated proteins of nonmuscle cells, our present knowledge of their biochemistry is critically appraised from the perspective that understanding complex cellular processes depends ultimately on the identification, purification, and biochemical characterization of the proteins involved. Although few conclusions are reached, possible molecular mechanisms for cellular regulation of actin polymerization, filament association, actomyosin ATPase activity, and mechanochemical coupling are discussed and a number of potentially fruitful directions for further research are suggested. These include comparative biochemical investigations and the study of the interaction of heterologous proteins, but particular emphasis is given to the need for quantitative studies at the molecular level of motility proteins purified from a single cellular source.Three mechanisms, ultrastructurally, biochemically, and mechanically distinct, have evolved for cell motility. Two of these, bacterial flagella (1, 2) and eukaryotic flagella (3-6), serve to move cells through fluid media, but they function differently. The third motile mechanism, that based on cytoplasmic microfilaments, is responsible for ameboid-type movement of a cell on a solid substratum. The major component of cytoplasmic microfilaments is the protein actin. Presumably, myosin (which is an ATPase that forms an enzymatically active complex with actin) provides the energy for the motility events, while a number of other proteins maintain the dynamic structural organization of the system and regulate its action. Similar systems in all eukaryotic cells (protist, plant, and animal, and including cells that also possess flagella) provide the mechanochemical basis for many other diverse cellular activities, including cytoplasmic streaming and saltatory movements, phagocytosis and secretory processes, cell division and possibly chromosome segregation, changes in cell shape, and probably even the regulation of the topographical distribution of membrane proteins and functional interconnections of the cell membrane with the nucleus (7-15). Some of these functions may have preceded in evolution the role of actin and myosin in ameboid movement. In their most recently evolved forms, actin and myosin comprise the highly structured contractile systems of muscles.Actomyosin-based cell motility and related phenomena such as the cytoskeletal role of microfilaments and the interaction of microfilaments with cell membranes are increasingly the subjects of investigation at the cellular level and in crude cell extracts. I believe, however, that to understand the physiology of cellular events it is first necessary to understand their biochemistry. It is necess...

Evidence that myosin does not contribute to force production in chromosome movement.

“…This reasoning is fueled by reports of the existence of two myosins in single non-muscle ceils (29,37,38,45). While we cannot rule out this …”

Second messenger regulation of occlusion of the spinal neurocoel in the chick embryo

“…It could also be argued that Ca2+ mediated its effect on neurocoel occlusion via a putative intrinsic mechanism: contraction of cytoplasmic actomyosin, considered to be a major force in bending the neural plate into a tube Nagele, 1985, 1988;Moran and Rice, 1976) and the invagination of the optic vesicle to form the optic cup (Brady and Hilfer, 1982). Furthermore, it is well known that actomyosin interaction in nonmuscle cells is a process dependent on Ca2+ (Brady and Hilfer, 1982;Cohen and de Vries, 1973;Korn, 1978) and calmodulin (Cheung, 1980;Yerna et al, 1979). However, when Desmond and Schoenwolf (1986) treated embryos with cytochalasin D a t concentrations effective in depolymerizing microfilaments, the neurocoels remained occluded.…”

Multiple tropomyosin polypeptides in chicken embryo fibroblasts: differential repression of transcription by Rous sarcoma virus transformation.

“…However, two forms of nonmuscle TM with significantly larger apparent molecular weights of 35,000 and 33,000 were identified in the cytoskeleton of cultured chicken embryo fibroblasts (25). More recently, multiple forms of TM having a broad range of molecular weights have been identified in the cytoskeleton of human fibroblasts (44) and in microfilaments of a variety of other cultured mammalian cells (35,36).It is commonly believed that microfilaments play a major role in cell motility and cell shape changes (7,18,27). A general feature of oncogenic transformation is the morphological alteration of the cell (for reviews, see references 23 and 45).…”

“…It is commonly believed that microfilaments play a major role in cell motility and cell shape changes (7,18,27). A general feature of oncogenic transformation is the morphological alteration of the cell (for reviews, see references 23 and 45).…”