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Filament formation and actin-activated ATPase activity are abolished by proteolytic removal of a small peptide from the tip of the tail of the heavy chain of Acanthamoeba myosin II



Filament formation and actin-activated ATPase activity are abolished by proteolytic removal of a small peptide from the tip of the tail of the heavy chain of Acanthamoeba myosin II



Journal of Biological Chemistry 260(3): 1967-1972



Actin-activated Mg2+-ATPase activity of myosin II from A. castellanii is regulated by phosphorylation of 3 serine residues located at the carboxyl-terminal end of each of the two 185,000-Da heavy chains; the phosphorylated molecule has full Ca2+-ATPase activity but no actin-activated Mg2+-ATPase activity. Under controlled conditions, chymotrypsin removes a small peptide containing all 3 phosphorylation sites from the ends of the myosin II H chains producing a molecule with heavy chains of 175,000 Da and undigested L chains. The length of the myosin II tail decreased from 89-76 nm. Chymotrypsin-cleaved myosin II has complete Ca2+-ATPase activity but no actin-activated Mg2+-ATPase activity under standard assay conditions and binds to F-actin and undigested myosin II in the absence, but not in the presence, of MgATP. In the presence of MgCl2, undigested myosin II forms biopolar filaments but chymotrypsin-cleaved myosin II forms only parallel (monopolar) dimers, as assessed by analytical ultracentrifugation and rotary shadow electron microscopy. Thus, the short segment very near the end of the myosin II tail that contains the 3 phosphorylatable serines is necessary for the formation of bipolar filaments and, probably as a consequence of filament formation, for the high-affinity binding of myosin II to F-actin in the presence of ATP and the actin-activated Mg2+-ATPase activity of native myosin II. This supports the previous conclusion that actin-activated Mg2+-ATPase of native myosin II is expressed only when the enzyme is in bipolar filaments with the proper conformation as determined by the state of phosphorylation of the H chains.

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Accession: 001368514

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PMID: 3155741



Related references

Filament formation and actin activated atpase activity are abolished by proteolytic removal of a small peptide from the tip of the tail of the heavy chain of acanthamoeba castellanii myosin ii. Journal of Biological Chemistry 260(3): 1967-1972, 1985

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