Structure And Function Study Of Metal Regulatory Protein MerR & Zinc Sensing Domain Of Histidine Kinase CzcS

Metal elements have significant influence on the living organisms,Proper concentration of them are necessary for the proceeding of biological activities.To maintain the balance of metal ions inside,the organisms have developed a series of regulatory mechanism to control the metal ions'uptake,efflux,intracellular trafficking,and storage.The objects in the study are the metal regulatory protein MerR who is in regulation of mercury(?)and the histidine kinase CzcS who is in regulation of zinc(?)in the bacterial.The structures,properties,and regulatory mechanisms of them are analyzed and discussed.The metalloprotein MerR is the transcriptional activator which responds to mercury(?)with extraordinary sensitivity and selectivity.During the past 30 years,considerable research focused on the characteristics of MerR have been performed in the Tn501 and Tn21 MerR from Gram-negative bacteria.To identify the molecular mechanism by which mercury(?)-binding modulates the function of MerR,we analyzed the crystal structure of Tn501 MerR bound to mercury(?).In Tn501 MerR,the three-conserved cysteine residues Cys82,Cys117,and Cys126 form structure with mercury(?)that shows trigonal planar coordination geometry.The unique coordination configuration,as well as the closed and hydrophobic environment of the metal-binding domain,provide MerR with high affinity for mercury(?).Based on the structure information,we propose the allosteric network for the transmission of mercury(?)-binding signal that links the C-terminal metal-binding domain and the N-terminal DNA-binding domain.The previous mutagenesis analyses have shown that in addition to the mercury ion coordinated ligands,any mutation near or at the residues that involved in the allosteric pathway lead MerR defective in repressive or activated function.Thus,both the unique coordination geometry and the precise coordination of the functional domains are required for high specific response of MerR for mercury(?).In Pseudomonas aeruginosa,the CzcR-CzcS signal transduction system is primarily important for its co-regulation of cross-resistance between heavy metals(zinc,cadmium,and cobalt)and carbapenem antibiotic.Additionally,it regulates several crucial genes involved in the control of quorum sensing and virulence factors.Despite the well-established intracellular regulatory pathway,it's still unclear how do the extracellular sensor domain of the histidine kinase CzcS respond the zinc ion stimulus and further trigger for the signal transduction.In this study,we have determined the crystal structure of CzcS sensor domain in complex with zinc ion.It is the first characterized heavy metal implicated sensor domain of two-component signal transduction system.The CzcS sensor exhibits as functional dimer with a mixed?/?-fold similar to PhoQ-DcuS-CitA(PDC)superfamily member,it contains the N-terminal helix-turn-helix domain and the five central anti-parallel ?-sheets that are connected by ?-helix.The metal ion zinc adopted distorted tetrahedral geometry with the symmetry related residues His55,Asp60 at the central H1 and H1'?-helices.The zinc induced association of H1 and H1'?-helices is physiologically important for signal transduction.A promising model,with the comparison to other PDC sensor folds,is put forward that the zinc-binding at the dimer interface causes the shift of the H1 and H1'?-helices and further induces the helical interactions rearrangement in the transmembrane regions.This model provides initial insights into the molecular mechanism of zinc ion sensing and signal transduction in CzcR-CzcS two-component system.