Myosin-I moves actin filaments on a phospholipid substrate: implications for membrane targeting.
Acanthamoeba myosin-I bound to substrates of nitrocellulose or planar lipid membranes on glass moved actin filaments at an average velocity of 0.2 micron/s. This movement required ATP and phosphorylation of the myosin-I heavy chain. We prepared planar lipid membranes on a glass support by passive fusion of lipid vesicles (Brian, A. A., and H. M. McConnell. 1984. Proc. Natl. Acad. Sci. USA. 81:6159-6163) composed of phosphatidylcholine and containing 0-40% phosphatidylserine. The mass of lipid that bound to the glass was the same for membranes of 2 and 20% phosphatidylserine in phosphatidylcholine and was sufficient to form a single bilayer. Myosin-I moved actin filaments on planar membranes of 5-40% but not 0-2% phosphatidylserine. At the low concentrations of phosphatidylserine, actin filaments tended to detach suggesting that less myosin-I was bound. We used the cooperative activation of Acanthamoeba myosin-I ATPase by low concentrations of actin to assess the association of phospholipids with myosin-I. Under conditions where activity depends on the binding of actin to the tail of myosin-I (Albanesi, J. P., H. Fujisaki, and E. D. Korn. 1985. J. Biol. Chem. 260:11174-11179), phospholipid vesicles with 5-40% phosphatidylserine inhibited ATPase activity. The motility and ATPase results demonstrate a specific interaction of the tail of myosin-I with physiological concentrations of phosphatidylserine. This interaction is sufficient to support motility and may provide a mechanism to target myosin-I to biological membranes.
Zot
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HG
Department of Cell Biology and Anatomy, Johns Hopkins Medical School, Baltimore, Maryland 21205.
Doberstein
S K
SK
Pollard
T D
TD
D000048:Acanthamoeba / Q000201:enzymology; D000199:Actins / Q000502:physiology*; D000205:Actomyosin / Q000502:physiology*; D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000502:physiology; D002465:Cell Movement; D003101:Collodion; D005139:Eyeglasses; D066298:In Vitro Techniques; D008051:Lipid Bilayers; D008563:Membrane Lipids / Q000502:physiology*; D008856:Microscopy, Fluorescence; D009218:Myosins / Q000502:physiology*; D010718:Phosphatidylserines / Q000502:physiology; D010743:Phospholipids / Q000502:physiology*
D000199:Actins; D008051:Lipid Bilayers; D008563:Membrane Lipids; D010718:Phosphatidylserines; D010743:Phospholipids; D003101:Collodion; D000205:Actomyosin; D009218:Myosins