Sensing ligands by periplasmic sensing histidine kinases with sensory PAS domains
H. Kneuper, P. Scheu, M. Etzkorn, M. Sevvana, P. Dünnwald, S. Becker, M. Baldus, C. Griesinger, and G. Unden
from: Sensory Mechanisms in Bacteria: Molecular Aspects of Signal Recognition (Edited by: Stephen Spiro and Ray Dixon). Caister Academic Press, U.K. (2010)
Structural analysis demonstrated that the sensing domains from extracellular sensing histidine kinases revealed frequently the presence of a PAS domains with an untypical fold (PDC or periplasmic PASP fold). The PDC/PASP-fold differs from the common PAS-fold of cytoplasmic PAS domains. The structures of the PDC domains of the PDC domains of the tri- and dicarboxylate sensors CitA, DcuS and DctB, the antimicrobial peptide/divalent cation sensor PhoQ, and the quorum sensor LuxQ provide insights into mechanisms of signal perception. Different modes of signal processing were suggested despite similar folds of the PDC domains. The structures of the PDC/PASP domain of CitA in the citrate-bound and citrate-free form show contraction of the domain after citrate binding and suggest a vectorial movement of transmembrane helix TM2 to the periplasmic side, and signal transduction across the membrane by a piston-type movement. Structural information on signal transfer from the membrane to the kinase was elaborated for a membrane-embedded construct of DcuS. DcuS contains a cytoplasmic PAS (PASC) domain with a typical PAS-fold as a linker between TM2 and the kinase domain. PASC shows high intrinsic plasticity. It is suggested that the signal induced movement of TM2 is perceived by PASC resulting in a partial resolution of PASC dimerization and signal transmission to the kinase domains. Further structural and biochemical information for this class of histidine kinases will hopefully increase our insight into the processes of signal perception and signal transduction by transmembrane sensor kinases read more ...