title: Characterization of Vibrio cholerae Hfq provides novel insights into the role of the Hfq C-terminal region.
abstract: Hfq is a bacterial RNA binding protein that facilitates small RNA-mediated posttranscriptional gene regulation. In Vibrio cholerae, Hfq and four Hfq-dependent small RNAs are essential for the expression of virulence genes, but little is known about this mechanism at the molecular level. To better understand V. cholerae Hfq structure and mechanism, we characterized the protein, alongside Escherichia coli Hfq for comparison, using biochemical and biophysical techniques. The N-terminal domain (NTD) of the two proteins is highly conserved, but the C-terminal regions (CTRs) vary in both sequence and length. Small-angle X-ray scattering studies showed that both proteins adopt a star-shaped hexameric structure in which the conserved NTD adopts the expected Sm fold while the variable CTR is disordered and extends radially outwards from the folded core. Despite their structural similarity, SDS-PAGE stability assays and collision-induced dissociation mass spectrometry revealed that the V. cholerae hexamer is less stable than that of E. coli. We propose that this is due to minor differences between the intersubunit interface formed by the NTDs and the ability of the E. coli CTR to stabilize this interface. However, based on electrophoretic mobility shift assays, the divergent CTRs do appear to perform a common function with regard to RNA-binding specificity. Overall, the similarities and differences in the fundamental properties of V. cholerae and E. coli Hfq provide insight into their assembly and molecular mechanisms.
authors.affiliation: Biophysics Laboratories, School of Biological Sciences, Institute of Biomedical and Biomolecular Sciences, University of Portsmouth, Portsmouth, UK.
authors.forename: Helen A
authors.initials: HA
authors.lastname: Vincent
authors.forename: Charlotte A
authors.initials: CA
authors.lastname: Henderson
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Ragan
authors.forename: Acely
authors.initials: A
authors.lastname: Garza-Garcia
authors.forename: Peter D
authors.initials: PD
authors.lastname: Cary
authors.forename: Darren M
authors.initials: DM
authors.lastname: Gowers
authors.forename: Marc
authors.initials: M
authors.lastname: Malfois
authors.forename: Paul C
authors.initials: PC
authors.lastname: Driscoll
authors.forename: Frank
authors.initials: F
authors.lastname: Sobott
authors.forename: Anastasia J
authors.initials: AJ
authors.lastname: Callaghan
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D035001:Host Factor 1 Protein / Q000737:chemistry* / Q000502:physiology; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D012329:RNA, Bacterial; D016601:RNA-Binding Proteins / Q000737:chemistry; D040681:Structural Homology, Protein; D014734:Vibrio cholerae / Q000737:chemistry* / Q000472:pathogenicity; D014774:Virulence / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C087373:Hfq protein, E coli; D035001:Host Factor 1 Protein; D012329:RNA, Bacterial; D016601:RNA-Binding Proteins