# Phosphorylation at $$Ser^{26}$$ in the ATP-Binding Site of $$Ca^{2+}$$/Calmodulin-Dependent Kinase II as a Mechanism for Switching off the Kinase Activity

 Title: Phosphorylation at $$Ser^{26}$$ in the ATP-Binding Site of $$Ca^{2+}$$/Calmodulin-Dependent Kinase II as a Mechanism for Switching off the Kinase Activity Author: Yilmaz, Mehtap; Gangopadhyay, Samudra Saurabh; Leavis, Paul Clifton; Grabarek, Zenon; Morgan, Kathleen G. Note: Order does not necessarily reflect citation order of authors. Citation: Yilmaz, Mehtap, Samudra Saurabh Gangopadhyay, Paul Clifton Leavis, Zenon Grabarek, and Kathleen G. Morgan. 2013. Phosphorylation at $$Ser^{26}$$ in the ATP-binding site of $$Ca^{2+}$$/calmodulin-dependent kinase II as a mechanism for switching off the kinase activity. Bioscience Reports 33(2): e00024. Full Text & Related Files: 3566533.pdf (993.5Kb; PDF) Abstract: CaMKII $$(Ca^{2+}$$/calmodulin-dependent kinase II) 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 $$Ser^{26}$$, a residue located within the ATP-binding site, terminates the sustained activity of the enzyme. To test the physiological importance of phosphorylation at $$Ser^{26}$$, we generated a phosphospecific $$Ser^{26}$$ antibody and demonstrated an increase in $$Ser^{26}$$ phosphorylation upon depolarization and contraction of blood vessels. To determine if the phosphorylation of $$Ser^{26}$$ affects the kinase activity, we mutated $$Ser^{26}$$ to alanine or aspartic acid. The S26D mutation mimicking the phosphorylated state of CaMKII causes a dramatic decrease in $$Thr^{287}$$ autophosphorylation levels and greatly reduces the catalytic activity towards an exogenous substrate (autocamtide-3), whereas the S26A mutation has no effect. These data combined with molecular modelling indicate that a negative charge at $$Ser^{26}$$ of CaMKII $$\gamma$$ inhibits the catalytic activity of the enzyme towards its autophosphorylation site at $$Thr^{287}$$ most probably by blocking ATP binding. We propose that $$Ser^{26}$$ phosphorylation constitutes an important mechanism for switching off CaMKII activity. Published Version: doi:10.1042/BSR20120116 Other Sources: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3566533/pdf/ Terms of Use: This article is made available under the terms and conditions applicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAA Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:10646382 Downloads of this work: