Tyrosine kinase activity of a Ca2+/calmodulin-dependent protein kinase II catalytic fragment |
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Authors: | Sugiyama Yasunori Ishida Atsuhiko Sueyoshi Noriyuki Kameshita Isamu |
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Institution: | a Department of Life Sciences, Faculty of Agriculture, Kagawa University, Ikenobe 2393, Miki-cho, Kagawa 761-0795, Japan b Laboratory of Molecular Brain Science, Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521, Japan |
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Abstract: | A 30-kDa fragment of Ca2+/calmodulin-dependent protein kinase II (30K-CaMKII) is a constitutively active protein Ser/Thr kinase devoid of autophosphorylation activity. We have produced a chimeric enzyme of 30K-CaMKII (designated CX40-30K-CaMKII), in which the N-terminal 40 amino acids of Xenopus Ca2+/calmodulin-dependent protein kinase I (CX40) were fused to the N-terminal end of 30K-CaMKII. Although CX40-30K-CaMKII exhibited essentially the same substrate specificity as 30K-CaMKII, it underwent significant autophosphorylation. Surprisingly, its autophosphorylation site was found to be Tyr-18 within the N-terminal CX40 region of the fusion protein, although it did not show any Tyr kinase activity toward exogenous substrates. Several lines of evidence suggested that the autophosphorylation occurred via an intramolecular mechanism. These data suggest that even typical Ser/Thr kinases such as 30K-CaMKII can phosphorylate Tyr residues under certain conditions. The possible mechanism of the Tyr residue autophosphorylation is discussed. |
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Keywords: | BSA bovine serum albumin CaMK Ca2+/calmodulin-dependent protein kinase 30K-CaMKII 30-kDa catalytic fragment of Ca2+/calmodulin-dependent protein kinase II CaMKIx Ca2+/calmodulin-dependent protein kinase I from Xenopus laevis CX40 (CX10) N-terminal 40 (10) amino acids of CaMKIx |
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