Acanthamoeba myosin I heavy chain kinase is activated by phosphatidylserine-enhanced phosphorylation.
The actin-activated Mg2(+)-ATPase activities of myosins I from Acanthamoeba castellanii are fully expressed only when a single amino acid on their heavy chain is phosphorylated by myosin I heavy chain kinase. Here we show that kinase isolated by a procedure designed to minimize its phosphorylation during purification can incorporate up to 7.5 mol of phosphate/mol of enzyme when incubated with ATP, possibly by autophosphorylation. The rate of phosphorylation is enhanced about 20-fold by phosphatidylserine but is unaffected by calcium ions. Phosphorylation increases the rate at which the kinase phosphorylates the regulatory site of myosin I by about 50-fold. These results suggest that (auto?)phosphorylation may regulate the activity of myosin I heavy chain kinase in vivo. The stimulation of kinase phosphorylation by phosphatidylserine (other phospholipids have not yet been tested) is of particular interest because myosin I has been shown to be tightly associated with membranes, especially the plasma membrane.
Brzeska
H
H
Laboratory of Cell Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892.
Lynch
T J
TJ
Korn
E D
ED
D000048:Acanthamoeba / Q000201:enzymology*; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004789:Enzyme Activation; D007700:Kinetics; D010718:Phosphatidylserines / Q000494:pharmacology*; D010766:Phosphorylation; D010770:Phosphotransferases / Q000302:isolation & purification / Q000378:metabolism*; D015800:Protozoan Proteins
D010718:Phosphatidylserines; D015800:Protozoan Proteins; D010770:Phosphotransferases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C033142:myosin-heavy-chain kinase; D017301:Ca(2+) Mg(2+)-ATPase