A Novel Protein Kinase Activity Identified from Human Breast Cancer Cell Lines

Abstract

Protein kinases (PKs) represent a diverse number of enzymes that exert a critical role in posttranslational changes on polypeptide structure and function (1,2). They catalyze the covalent transfer of phosphate from two common donors, ATP or GTP, to serine, threonine, and tyrosine residues located on its own molecule, endogenous cellular or exogenous protein acceptors, or synthetic aminoacidic sequences. Regarding their function it is well established that PKs regulate diverse physiological processes such as metabolic pathways, gene expression, membrane transport of ions and metabolites, cell cycle, nervous transmission, and cell transformation and differentiation (3). At the same time, they are dependent for their regulation on a number of activators or inhibitors with the exception of oncogenic transforming PK (4). The former group, the regulated one, in basal stage exhibited a low level of activity due to interaction of an “autoinhibitory” domain located within the enzyme at the catalytic site in a way that blocked the binding with the substrates (5). The enzyme is activated by an allosteric activator that induces a conformational change in the autoinhibitory domain allowing the enzyme to release its catalytic capability.