PNNL

Abstract

ABSTRACT-Although most two-component signal transduction systems (TCSTS) use a simple phosphotransfer pathway from one histidine kinase (HK) to one response regulator (RR), a multiple-step phosphorelay involving a phosphotransfer scheme of His-Asp-His-Asp was discovered in recent years. Central to this multiple-step type signal transduction pathway are a hybrid-type HK, containing both an HK kinase domain and a RR receiver domain in a single protein, and a histidine-containing phosphotransfer (HPT) that can exist as either a domain in hybrid-type HKs or as a separate protein. While multiple-step phosphorelay systems predominant in eukaryotes, it has been previously suggested that they are less common in prokaryotes. In this study, we found that putative hybrid-type HKs were present in 56 out of 156 complete prokaryotic genomes, indicating that multiple-step phosphorelay systems are more common in prokaryotes than previously appreciated. Large expansions of hybrid-type HKs were observed in several types of bacterial species, including cyanobacteria, several bacteria involved in bacteria-eukaryote interaction, and metabolically versatile bacteria. Phylogenetic analysis indicated that there was no common ancestor for hybrid-type of HKs, and their origin and expansion was achieved by lateral recruitment of a receiver domain into an HK molecule and then duplication as one unit. Lateral recruitment of additional sensory domains such as PAS was also evident. HPT domains or proteins were identified in 32 of the genomes with hybrid-type HKs, however, no significant gene expansion was observed for HPTs even in genome with large number of hybrid-type HKs. In addition, the observation of fewer HPTs than hybrid-type HKs in almost all genomes studied suggests that there is no simple one-to-one relationship between them