Crystal structure of a histidine kinase sensor domain with similarity to periplasmic binding proteins.

摘要

Histidine kinase receptors are elements of the two-component signal transduction systems commonly found in bacteria and lower eukaryotes, where they are crucial for environmental adaptation through the coupling of extracellular changes to intracellular responses. The typical two-component system consists of a membrane-spanning histidine kinase sensor and a cytoplasmic response regulator. In the classic system, extracellular signals such as small molecule ligands and ions are detected by the periplasmic sensor domain of the histidine kinase receptor, which modulates the catalytic activity of the cytoplasmic histidine kinase domain and promotes ATP-dependent autophosphorylation of a conserved histidine residue. The phosphate is subsequently transferred to a conserved aspartate of the cognate response regulator through a phospho-transfer mechanism, and the activity of the response regulator is modulated in turn. The response regulator often controls gene transcription or flagellar rotation, and thus allows cellular adaptation to an environmental signal. The nature of histidine kinase sensor proteins is such that the catalytic domain and other cytoplasmic elements are conserved whereas the sensor domains are modular and highly variable in sequence. Thousands of histidine kinases have been identified through genome sequencing projects, but many of these remain biochemically unchar-acterized. As part of a structural genomics project aimed at understanding the structural relationships between all known sensor domains, we have solved the structure of a previously uncharacterized sensor domain from a histidine kinase protein encoded by the Geobacter sulfurredu-cens GSU2755 gene, originally identified and annotated through genome sequencing of the organism. We use the name HK29_s for this putative sensor domain. The structure reveals a previously uncharacterized histidine kinase sensor domain fold.