The G-rich loop, or ATP-binding loop, is a region of ePK kinases that binds the core of ATP. The typical sequence motif is GxGxxG, with the ATP interacting with the backbones of the peptide chain, and the short side-chains of the glycines giving extra flexibility. The Gs are named G50, G52 and G55 after the numbering of the original PKA structure. G52 is the most conserved, and generally found in other PKL kinases as well. The G52 backbone co-ordinates the gamma phosphate of the ATP and facilitates phosphoryl transfer. |CDKs and many other CMGC kinases have a GxGxYG in which the Y can be phosphorylated (by Wee1, for CDK1) to inhibit kinase activity.