Characterization of myosin-II binding to Golgi stacks in vitro.
In addition to important roles near the actin-rich cell cortex, ample evidence indicates that multiple myosins are also involved in membrane movements in the endomembrane system. Nonmuscle myosin-II has been shown to have roles in anterograde and retrograde trafficking at the Golgi. Myosin-II is present on Golgi stacks isolated from intestinal epithelial cells and has been localized to the Golgi in several polarized and unpolarized cell lines. An understanding of roles of myosin-II in Golgi physiology will be facilitated by understanding the molecular arrangement of myosin-II at the Golgi. Salt-washing removes endogenous myosin-II from isolated Golgi and purified brush border myosin-II can bind in vitro. Brush border myosin-II binds to a tightly bound Golgi peripheral membrane protein with a K(1/2) of 75 nM and binding is saturated at 0.7 pmol myosin/microg Golgi. Binding studies using papain cleavage fragments of brush border myosin-II show that the 120-kDa rod domain, but not the head domain, of myosin heavy chain can bind directly to Golgi stacks. The 120-kDa domain does not bind to Golgi membranes when phosphorylated in vitro with casein kinase-II. These results suggest that phosphorylation in the rod domain may regulate the binding and/or release of myosin-II from the Golgi. These data support a model in which myosin-II is tethered to the Golgi membrane by its tail and actin filaments by its head. Thus, translocation along actin filaments may extend Golgi membrane tubules and/or vesicles away from the Golgi complex.
Fath
Karl R
KR
Biology Department, Queens College and Graduate Center of the City University of New York, Flushing, NY 11367, USA. kfath@forbin.qc.edu
D000199:Actins / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002645:Chickens; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D007413:Intestinal Mucosa / Q000502:physiology* / Q000648:ultrastructure; D024462:Myosin Type II / Q000378:metabolism*; D011485:Protein Binding
D000199:Actins; D024462:Myosin Type II