Mapping of the adenosine 5'-triphosphate binding site of type II calmodulin-dependent protein kinase

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Abstract
The specificity of the ATP-binding site of the type II calmodulin-dependent protein kinase was probed with 25 analogues of ATP modified at various positions of the molecule. The analogues were compared by their ability to compete with ATP in the protein kinase reaction. The result of this comparison indicates that the enzyme is most sensitive to modificatons at, or replacement of, the purine moiety. Changes at the triphosphate chain are much better tolerated, although the enzyme exhibited a selective sensitivity to changes in the conformation of this group. The smallest contribution to the specificity of ATP binding appears to be made by the ribose ring. The Ki values obtained for a subset of these analogues were compared to those previously reported for phosphorylase b kinase and the cyclic nucleotide dependent protein kinases [Flockhart, D. A., Friest, W., Hoppe, J., Lincoln, T. M., and Corbin, J. D. (1984) Eur. J. Biochem. 140, 289-295]. A striking similarity in the responses of these protein kinases to modifications of the aTP molecule sugests that the type II calmodulin-dependent protein kinase is related to these enzymes. Support for this conclusion was provided, recently, through comparisons of the deduced primary structures of the .alpha. and .beta. subunits of the type II calmodulin-dependent protein kinase with the protein sequences of the catalytic subunits of phosphorylase b kinase and cAMP-dependent protein kinase [Hanley, R. M., Means, A. R., Ono, T., Kemp, B. E., Burgin, K. E., Waxham, N., and Kelly, P. T. (1987) Science (Washington, D. C.) 237, 293-297; Bennett, M. K., and Kennedy, M. B. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 1794-1798], which indicated areas of extensive homology.

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