This family represents the N-terminal region of Hpr Serine/threonine kinase PtsK. This kinase is the sensor in a multicomponent phospho-relay system in control of carbon catabolic repression in bacteria [1]. This kinase in unusual in that it recognises the tertiary structure of its target and is a member of a novel family unrelated to any previously described protein phosphorylating enzymes [1]. X-ray analysis of the full-length crystalline enzyme from Staphylococcus xylosus at a resolution of 1.95 A shows the enzyme to consist of two clearly separated domains that are assembled in a hexameric structure resembling a three-bladed propeller. The blades are formed by two N-terminal domains each, and the compact central hub assembles the C-terminal kinase domains [2].

1: A novel protein kinase that controls carbon catabolite repression in bacteria. Reizer J, Hoischen C, Titgemeyer F, Rivolta C, Rabus R, Stulke J, Karamata D, Saier MH Jr, Hillen W; Mol Microbiol 1998;27:1157-1169. PMID:9570401

2: Structure of the full-length HPr kinase/phosphatase from Staphylococcus xylosus at 1.95 A resolution: Mimicking the product/substrate of the phospho transfer reactions. Marquez JA, Hasenbein S, Koch B, Fieulaine S, Nessler S, Russell RB, Hengstenberg W, Scheffzek K; Proc Natl Acad Sci U S A 2002;99:3458-3463. PMID:11904409