Mammalian Histidine Kinase and Phosphohistidine Detection

An increase in the incidence of histidine phosphorylation of histone H4 in mammalian cells appears to be causally associated with an increase in cellular proliferation (1). Although this and many other reports of histidine phosphorylation in mammalian cells are documented in the literature, little is understood about their biological roles by comparison to hydroxyaminoacid kinases. Many of the reasons for this lack of understanding stem from difficulties associated with the study of the acid-labile phosphoramidate (P-N) bond of phosphohistidine. The acid-labile nature of phosphohistidine has meant that traditional kinase purification and phosphoamino acid detection methods are not applicable to this class of kinase. With recent developments and adaptations of traditional methods, the detection and assay of histidine kinases is now slowly revealing some of the biological processes histidine kinases and protein histidine phosphorylation are involved in. These methods now include one and two-dimensional in-gel kinase assays of histone H4 histidine kinases and mass spectrometric methods for the detection of phosphohistidines in proteins. In order to examine the relationship between histidine kinase activity and cellular proliferation in liver tissue we have adopted many of these methods. By examining the levels of histidine kinase activity both before and after the liver has undergone various physical and biological perturbations, we hypothesize that histidine kinase activity may function as an oncodevelopmental marker (2). The next step in the process is to utilize these techniques that are geared toward the study of acid-labile phosphorylation to identify and characterize the kinases associated with increased activity in proliferating liver tissue. (1) Besant et al. (2003) Mammalian protein histidine kinases. Int. J. Biochem. and Cell Biol. 69: 183–215. (2) Tan et al. (2004) Histone H4 histidine kinase displays the expression pattern of a liver oncodevelopmental marker. Carcinogenesis 25:2083–2088. B.2 Separation of Histone H3 for the Characterization of the Intact Protein and Its Modifications