Cell, Vol. 93, 1-4, April 3, 1998
In partnership with actin cytoskeletal filaments, at least 15 classes of myosins accomplish diverse tasks in cell motility such as muscle contraction, chemotaxis, cyto- kinesis, pinocytosis, targeted vesicle transport and, possibly, signal transduction (Mermall et al., 1998). Bio- chemical and mechanical studies have established the link between elementary events in the actomyosin ATPase cycle and work output (Cooke, 1997), but the associated changes in molecular structure are still vague. X-ray crystallography (Rayment et al., 1996), in vitro mechan- ics of the purified proteins, mutagenesis (Sweeney and Holzbaur, 1996), and time-resolved structural studies on muscle fibers (Irving and Piazzesi, 1997) are providing new insights into this problem. Data from of all of these approaches must be integrated to understand energy transduction by motor proteins.
The typical design in cell motility of a motor protein neously attached is uncertain (Cooke, 1997; Linari et al., sliding along a linear filamentous track was first discovered in muscle cells because these elegant machines express and assemble concentrated and highly periodic interdigitating arrays of myosin and actin filaments that are particularly amenable to structural, mechanical, and biochemical studies (reviewed by Cooke, 1997). The fila-ments do not change length when the muscle contracts, but they slide relative to each other using energy liber-ated by hydrolysis of ATP to ADP and phosphate (Pi ).