Protein kinase C alpha (PKCα) is an enzyme that in humans is encoded by the PRKCA gene.
Function
Protein kinase C (PKC) is a family of serine- and threonine-specific protein kinases that can be activated by calcium and the second messenger diacylglycerol. PKC family members phosphorylate a wide variety of protein targets and are known to be involved in diverse cellular signaling pathways. PKC family members also serve as major receptors for phorbol esters, a class of tumor promoters. Each member of the PKC family has a specific expression profile and is believed to play a distinct role in cells. The protein encoded by this gene is one of the PKC family members. This kinase has been reported to play roles in many different cellular processes, such as cell adhesion, cell transformation, cell cycle checkpoint, and cell volume control. Knockout studies in mice suggest that this kinase may be a fundamental regulator of cardiac contractility and Ca2+ handling in myocytes.
Protein kinase C-alpha (PKC-α) is a specific member of the protein kinase family. These enzymes are characterized by their ability to add a phosphate group to other proteins, thus changing their function. PKC-α has been widely studied in the tissues of many organisms including drosophila, xenopus, cow, dog, chicken, human, monkey, mouse, pig, and rabbit. Many studies are currently being conducted investigating the structure, function, and regulation of this enzyme. The most recent investigations concerning this enzyme include its general regulation, hepatic function, and cardiac function.
Regulation
PKC-α is unique in its mode of regulation compared to other kinases within this family. In general, the protein kinase family is regulated by allosteric regulation, the binding of a modulating molecule that effects a conformational change in the enzyme and thus a change in the enzyme's activity. The primary mode of PKC-α's regulation, however, involves its interaction with the cell membrane, not direct interaction with specific molecules. The cell membrane consists of phospholipids. At warmer temperatures, phospholipids exist in a more fluid state as a result of increased intramolecular motion. The more fluid the cell membrane, the greater PKC-α's activity. At cooler temperatures, phospholipids are found in a solid state with constricted motion. As phospholipids become stationary, they assume a particular orientation within the membrane. Phospholipids that solidify at an irregular or angled orientation with respect to the membrane, can reduce PKC-α's activity.
The composition of the cell membrane can also affect PKC-α's function. The presence of calcium ions, magnesium ions, and diacylglycerols (DAGs) are the most important because they influence the hydrophobic domain of the membrane. Varying concentrations of these three components constitute a longer or shorter length of the hydrophobic domain. Membranes with long hydrophobic domains result in decreased activity because it is harder for PKC-α to insert into the membrane. At low concentrations, the hydrophobic domain is shorter allowing PKC-α to readily insert into the membrane and its activity increases.
Secondary structure
Using infrared spectroscopy techniques, researchers have demonstrated that the secondary structure of PKC alpha consists of around 44% beta sheets and nearly 22% alpha helices at 20 °C. Upon addition of calcium ions, a slight increase in beta sheets to 48% was observed. Additional ligands normally associated with PKC alpha, such as PMA, ATP, and phospholipids had no effect on secondary structure.
The structure of PKC alpha was better preserved during denaturation of the enzyme at 75 °C in the presence of calcium ions than in their absence. In one study, beta sheet composition only decreased by 13% with calcium ions present compared to 19% when absent.