Autophosphorylation-independent activation of Acanthamoeba myosin I heavy chain kinase by plasma membranes.
The three isoforms of Acanthamoeba myosin I (non-filamentous myosin with only a single heavy chain) express actin-activated Mg(2+)-ATPase activity only when phosphorylated at a single site by myosin I heavy chain kinase. The kinase is activated by autophosphorylation that is greatly stimulated by acidic phospholipids. Substantial fractions of the three myosins I and the kinase are associated in situ with membranes, and all four enzymes bind to purified membranes in vitro. We now report that when kinase and myosin I are incubated together with phosphatidylserine vesicles not only does the kinase autophosphorylate more rapidly than soluble kinase in the absence of phosphatidylserine but that, probably as a result, the kinase phosphorylates myosin I more rapidly than soluble kinase phosphorylates soluble myosin I. Similarly, plasma membrane-bound kinase phosphorylates membrane-bound myosin I and activates its actin-activated Mg(2+)-ATPase activity more rapidly than soluble kinase phosphorylates and activates soluble myosin I in the absence of membranes. However, the enhanced activity of membrane-bound kinase (which is comparable to the activity of kinase in the presence of phosphatidylserine) is not due to autophosphorylation of the membrane-bound kinase, which is very much slower than for kinase activated by phosphatidylserine vesicles.
Kulesza-Lipka
D
D
Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892.
Brzeska
H
H
Baines
I C
IC
Korn
E D
ED
D000048:Acanthamoeba / Q000201:enzymology*; D000595:Amino Acid Sequence; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D006706:Homeostasis; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D009218:Myosins / Q000302:isolation & purification / Q000378:metabolism*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000302:isolation & purification / Q000378:metabolism*; D015800:Protozoan Proteins; D013379:Substrate Specificity
D007527:Isoenzymes; D015800:Protozoan Proteins; D010770:Phosphotransferases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C033142:myosin-heavy-chain kinase; D017301:Ca(2+) Mg(2+)-ATPase; D009218:Myosins