Conformational diversity of catalytic cores of protein kinases

X-ray crystallography of the protein kinase family has provided an impressive array of crystal structures, setting the stage for rational design of specific inhibitors of these vitally important regulators of the signaling pathways of the cell. Initial work on the first crystal structure of a protein kinase, cyclic AMP-dependent protein kinase, has provided evidence of conformational changes suggested to be critical for the common catalytic event of transferring the gamma phosphate from ATP onto the targeted protein. This review updates the current status of the extent of conformational diversity of the protein kinase family and suggests that both the nature and the extent of those changes can provide a rationale for the increased occurrence of specific protein kinase inhibitors targeted at the ATP-binding site. It focuses on the fact that in addition to the sequence diversities in ATP binding clefts reported recently, there is conformational diversity in the beta sheets of the upper domains of the catalytic cores. This difference is directly related to the regulation of kinases by multiple mechanisms.