Protein Kinase A (PKA)
Background on Protein Kinases
Protein kinases catalyze the transfer of the γ -phosphoryl group of adenosine triphosphate (ATP) to an amino acid hydroxyl group (commonly serine, threonine, or tyrosine) of a substrate (Reaction Scheme 1).
Reaction Scheme 1:
The protein kinase family makes up approximately 2000 enzymes in humans, and estimates project that approximately 30% of all proteins encoded by the human genome undergo reversible phosphorylation. Abnormal phosphorylation is recognized as a cause or repercussion of numerous diseases such as cancer, diabetes, and rheumatoid arthritis, in fact, the cancer treatment drugs cyclosporine and rapamycin act to inhibit phosphorylation activity. Thus, a complete understanding of these reversible phosphorylation events represents perhaps one of the most important factors in specific understanding of biological function and has vast implications on approaches for the treatment of disease.
PKA and Ca2+ in Cardiomyocytes
Protien Kinase A (PKA), a 350 residue kinase, is responsible for the phosphorylation of phospholamban (PLB), thus allowing PLB to relieve its regulatory inhibition of the sarcoendoplasmic reticulum calcium ATPase (SERCA). This relief of inhibition allows movement of calcium into the lumen of the endoplasmic reticulum which generates relaxation of the cardiomyocyte. We are currently completing the full backbone assignment of PKA using solution NMR. This assignment is based on TROSY-type multidimensional NMR experiments (HNCA, HN(CO)CA, HNCACB, HNCO, and HN(CA)CO) and 15N/ 1H-HSQC spectra of selective 15N amino acid labeled PKA using isotopically 15N enriched amino acids.