title: Structural insights into the molecular mechanism of Escherichia coli SdiA, a quorum-sensing receptor.
abstract: Escherichia coli SdiA is a quorum-sensing (QS) receptor that responds to autoinducers produced by other bacterial species to control cell division and virulence. Crystal structures reveal that E. coli SdiA, which is composed of an N-terminal ligand-binding domain and a C-terminal DNA-binding domain (DBD), forms a symmetrical dimer. Although each domain shows structural similarity to other QS receptors, SdiA differs from them in the relative orientation of the two domains, suggesting that its ligand-binding and DNA-binding functions are independent. Consistently, in DNA gel-shift assays the binding affinity of SdiA for the ftsQP2 promoter appeared to be insensitive to the presence of autoinducers. These results suggest that autoinducers increase the functionality of SdiA by enhancing the protein stability rather than by directly affecting the DNA-binding affinity. Structural analyses of the ligand-binding pocket showed that SdiA cannot accommodate ligands with long acyl chains, which was corroborated by isothermal titration calorimetry and thermal stability analyses. The formation of an intersubunit disulfide bond that might be relevant to modulation of the DNA-binding activity was predicted from the proximal position of two Cys residues in the DBDs of dimeric SdiA. It was confirmed that the binding affinity of SdiA for the uvrY promoter was reduced under oxidizing conditions, which suggested the possibility of regulation of SdiA by multiple independent signals such as quorum-sensing inducers and the oxidation state of the cell.
authors.affiliation: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Truc
authors.initials: T
authors.lastname: Kim
authors.affiliation: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Thao
authors.initials: T
authors.lastname: Duong
authors.affiliation: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Chun-ai
authors.initials: CA
authors.lastname: Wu
authors.affiliation: Department of Cosmetic Science, Chungwoon University, San 29, Namjang, Hongsung, Chungnam 350-701, Republic of Korea.
authors.forename: Jongkeun
authors.initials: J
authors.lastname: Choi
authors.affiliation: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Nguyen
authors.initials: N
authors.lastname: Lan
authors.affiliation: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Sung Wook
authors.initials: SW
authors.lastname: Kang
authors.affiliation: Department of Studies in Physics, University of Mysore, Manasagangotri, Mysore 570 006, India.
authors.forename: Neratur K
authors.initials: NK
authors.lastname: Lokanath
authors.affiliation: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: DongWoo
authors.initials: D
authors.lastname: Shin
authors.affiliation: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Hye-Yeon
authors.initials: HY
authors.lastname: Hwang
authors.affiliation: Department of Molecular Cell Biology, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon 440-746, Republic of Korea.
authors.forename: Kyeong Kyu
authors.initials: KK
authors.lastname: Kim
mesh_terms: D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D008024:Ligands; D008025:Ligases / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D053038:Quorum Sensing; D015398:Signal Transduction; D013045:Species Specificity; D015534:Trans-Activators / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D008024:Ligands; D015534:Trans-Activators; C490806:sdiA protein, E coli; D008025:Ligases; C449816:N-acylhomoserine lactone synthase
keywords: SdiA; disulfide bonds; oxidative stress; quorum sensing