Isoenzymes of Soybean Calcium-Dependent Protein Kinase

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Calcium-dependent protein kinase from soybean is the prototype for a new class of protein kinases having regulatory domains that are similar to calmodulin. The biochemical properties of this enzyme indicate that it plays a role in signal transduction pathways employing calcium as a second messenger. Recent evidence suggests that several isoenzymes of CDPK are present in soybean. Supporting this conclusion is the observation that the sequences of two cDNAs encoding soybean CDPK are approximately 70% identical. Isoenzymes having differing sensitivities to calcium, substrate specificities, and tissue distributions could provide the basis for differences in cellular responses to calcium. The objective of the proposed research is to identify and characterize isoenzymes of CDPK. The techniques of molecular biology, biochemistry, and immunology will be used to study the structure, function, regulation, and distribution of the CDPK isoenzymes. The cDNAs encoding the isoenzymes will be identified and expressed in Escherechia coli. The expressed isoenzymes will be purified and biochemically characterized. Antibodies that recognize specific isoenzymes will be made. Antibodies and cDNA probes will be used to determine the distribution of the isoenzymes in the plant. In addition the function and interaction of the catalytic and regulatory domains of CDPK will be studied through the expression in E. coli and subsequent characterization of the individual functional domains.