Phospholipid membrane-associated brush border myosin-I activity.
Brush border myosin-I (BBMI) is associated with the membrane of intestinal epithelial cells where it probably plays a structural role. BBMI also has been identified on Golgi-derived vesicles in intestinal epithelial cells where it may translocate vesicles into the brush border. However, the mechanochemical activity of BBMI bound to a phospholipid membrane has not been described. This study reports that phospholipid membrane-associated BBMI displays ATPase activity when bound to phospholipids, but does not move actin filaments when associated with a phospholipid bilayer. BBMI does not bind significantly to brush border membrane lipids, which contain about 16% phosphatidylserine (PS), in either a pelleting or planar membrane assay. Similarly, planar membranes containing 20% PS do not bind a significant amount of BBMI. Increasing the concentration of PS to 40% does result in the binding of BBMI to both vesicles and planar membranes. This binding is enhanced with increased Ca2+ concentrations. BBMI retains its ATPase activity when bound to phospholipid vesicles containing 40% PS. However, BBMI attached to a phospholipid bilayer surface does not move actin filaments, even though the amount of BBMI bound to the lipid surface, as reflected by the number of actin filaments associated with bilayer-bound BBMI, is sufficient to observe motility in control experiments. When membrane fluidity is reduced by adding cholesterol to the membrane lipids containing 40% PS, BBMI still binds to the membrane, but again no actin filament motility is observed. The lack of binding by BBMI to brush border membrane lipids and the absence of membrane-associated BBMI mechanical activity suggest that factors in addition to membrane lipids are necessary for membrane-associated myosin-I motility.
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Department of Physiology, University of Texas Southwestern Medical Center at Dallas 75235-9040, USA.
D008841:Actin Cytoskeleton / Q000378:metabolism; D000199:Actins / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002465:Cell Movement; D002645:Chickens; D004789:Enzyme Activation / Q000187:drug effects; D007421:Intestine, Small / Q000648:ultrastructure; D008081:Liposomes / Q000378:metabolism; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008567:Membranes, Artificial; D008871:Microvilli / Q000737:chemistry / Q000201:enzymology*; D009218:Myosins / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*
D000199:Actins; D008081:Liposomes; D008563:Membrane Lipids; D008565:Membrane Proteins; D008567:Membranes, Artificial; D010743:Phospholipids; D009218:Myosins