Abstract
The protein kinase C family of enzymes transduces the myriad of signals promoting lipid hydrolysis. The prevalence of this enzyme family in signaling is exemplified by the diverse transduction mechanisms that result in the generation of protein kinase C's activator, diacylglycerol. Signals that stimulate members of the large families of G protein-coupled receptors, tyrosine kinase receptors, or non-receptor tyrosine kinases can cause diacylglycerol production, either rapidly by activation of specific phospholipase Cs or more slowly by activation of phospholipase D to yield phosphatidic acid and then diacylglycerol(1, 2, 3) . In addition, fatty acid generation by phospholipase A2 activation modulates protein kinase C activity(3) . Thus, multiple receptor pathways feeding into multiple lipid pathways have the common end result of activating protein kinase C by production of its second messenger.
Highlights
Phorbol esters, potent tumor promoters, can substitute for diacylglycerol in activating protein kinase C [1,2,3]
This review discusses the structure of the protein kinase C family, its enzymatic function, and how structure and function are regulated by 1) cofactors and 2) phosphorylation
The function of each of these domains has been established by extensive biochemical and mutational analysis; the C1 domain contains a Cys-rich motif, duplicated in most isozymes, that forms the diacylglycerol/phorbol ester binding site (Fig. 1, orange) [7]; this domain is immediately preceded by an autoinhibitory pseudosubstrate sequence (Fig. 1, green) [10]; the C2 domain contains the recognition site for acidic lipids and, in some isozymes, the Ca2ϩ-binding site (Fig. 1, yellow) [9]
Summary
Residues in basic sequences but displays significantly less specificity than protein kinase A [29]. Recurring themes are that protein kinase C is involved in receptor desensitization, in modulating membrane structure events, in regulating transcription, in mediating immune responses, in regulating cell growth, and in learning and memory among many other functions. These and the functions of specific isozymes are described in a number of excellent reviews [1,2,3,4, 39]. A key regulator of protein kinase C function in vivo is likely to be subcellular distribution of both the enzyme and substrate [40]. Binding of ligands or, in some cases, substrate activates the enzyme by removing the pseudosubstrate from the substrate-binding site
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