Structure and function of the protein kinase C gene family
Protein kinase C is a serine/threonine protein kinase which is activated in the cell in response to production of diacylglycerol. Gene cloning has revealed the presence of a highly related family of enzymes, which can be sub-divided into groups on the basis of sequence conservation. Differences are seen in both isoform distribution and associated biochemical activity, for example in substrate specificity and activator requirements. Comparison of the protein sequences andin vitro activities of the protein kinase C isoforms has identified regions important for particular aspects of kinase function. Some of these regions are also found associated with other proteins, allowing confirmation of the assigned activity. Site-directed mutagenesis has confirmed the presence of an autoinhibitory sequence involved in protein kinase C regulation and generated constitutively activated proteins which can be used to study differential isoform function. These same sequences have been shown to play a role in substrate selection, perhaps by competition for binding to the active site. Protein kinase C is known to be a phosphoprotein and the identification of regulatory sites phosphorylated by a ‘PKC-kinase’ suggest a possible alternative route for regulation of protein kinase C activity.