title: The LcrG Tip Chaperone Protein of the Yersinia pestis Type III Secretion System Is Partially Folded.
abstract: The type III secretion system (T3SS) is essential in the pathogenesis of Yersinia pestis, the causative agent of plague. A small protein, LcrG, functions as a chaperone to the tip protein LcrV, and the LcrG-LcrV interaction is important in regulating protein secretion through the T3SS. The atomic structure of the LcrG family is currently unknown. However, because of its predicted helical propensity, many have suggested that the LcrG family forms a coiled-coil structure. Here, we show by NMR and CD spectroscopy that LcrG lacks a tertiary structure and it consists of three partially folded α-helices spanning residues 7-38, 41-46, and 58-73. NMR titrations of LcrG with LcrV show that the entire length of a truncated LcrG (residues 7-73) is involved in binding to LcrV. However, there is regional variation in how LcrG binds to LcrV. The C-terminal region of a truncated LcrG (residues 52-73) shows tight binding interaction with LcrV while the N-terminal region (residues 7-51) shows weaker interaction with LcrV. This suggests that there are at least two binding events when LcrG binds to LcrV. Biological assays and mutagenesis indicate that the C-terminal region of LcrG (residues 52-73) is important in blocking protein secretion through the T3SS. Our results reveal structural and mechanistic insights into the atomic conformation of LcrG and how it binds to LcrV.
authors.affiliation: Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045 USA.
authors.forename: Sukanya
authors.initials: S
authors.lastname: Chaudhury
authors.affiliation: Department of Microbiology and Immunology, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
authors.forename: Clarice
authors.initials: C
authors.lastname: de Azevedo Souza
authors.affiliation: Department of Microbiology and Immunology, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
authors.forename: Gregory V
authors.initials: GV
authors.lastname: Plano
authors.affiliation: Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045 USA. Electronic address: rdguzman@ku.edu.
authors.forename: Roberto N
authors.initials: RN
authors.lastname: De Guzman
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000942:Antigens, Bacterial / Q000737:chemistry / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D010930:Plague / Q000382:microbiology*; D052899:Pore Forming Cytotoxic Proteins / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D000069296:Type III Secretion Systems / Q000737:chemistry / Q000378:metabolism*; D015010:Yersinia pestis / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; C088009:LcrG protein, Yersinia; C043908:LcrV protein, Yersinia; D018832:Molecular Chaperones; D052899:Pore Forming Cytotoxic Proteins; D000069296:Type III Secretion Systems
keywords: LcrG; NMR; T3SS; Yersinia pestis; tip chaperone