Phosphorylation at Ser26 in the ATP binding site of Calcium Calmodulin dependent Kinase II as a mechanism for switching off the kinase activity.

Bioscience Reports (Impact Factor: 2.64). 01/2013; 33(2). DOI: 10.1042/BSR20120116
Source: PubMed


Calcium/calmodulin dependent kinase II (CaMKII) is a serine/threonine phosphotransferase that is capable of long-term retention of activity due to autophosphorylation at a specific threonine residue within each subunit of its oligomeric structure. The gamma isoform of CaMKII is a significant regulator of vascular contractility. Here we show that phosphorylation of CaMKII gamma at Ser26, a residue located within the ATP binding site, terminates the sustained activity of the enzyme. To test the physiological importance of phosphorylation at Ser26, we generated a phosphospecific Ser26 antibody and demonstrated an increase of Ser26 phosphorylation upon depolarization and contraction of blood vessels. To determine if the phosphorylation of Ser26 affects the kinase activity, we mutated Ser26 into Ala or Asp. The S26D mutation mimicking the phosphorylated state of CaMKII causes a dramatic decrease in Thr287 autophosphorylation levels and greatly reduces the catalytic activity towards an exogenous substrate (autocamtide-3), while the S26A mutation has no effect. These data combined with molecular modeling indicate that a negative charge at Ser26 of CaMKII gamma inhibits the catalytic activity of the enzyme towards its autophosphorylation site at Thr287 most likely by blocking ATP binding. We propose that Ser26 phosphorylation constitutes an important mechanism for switching off CaMKII activity.

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Available from: Kathleen G Morgan, Feb 05, 2014