title: Structural characterization of the RNA chaperone Hfq from the nitrogen-fixing bacterium Herbaspirillum seropedicae SmR1.
abstract: The RNA chaperone Hfq is a homohexamer protein identified as an E. coli host factor involved in phage Qβ replication and it is an important posttranscriptional regulator of several types of RNA, affecting a plethora of bacterial functions. Although twenty Hfq crystal structures have already been reported in the Protein Data Bank (PDB), new insights into these protein structures can still be discussed. In this work, the structure of Hfq from the β-proteobacterium Herbaspirillum seropedicae, a diazotroph associated with economically important agricultural crops, was determined by X-ray crystallography and small-angle X-ray scattering (SAXS). Biochemical assays such as exclusion chromatography and RNA-binding by the electrophoretic shift assay (EMSA) confirmed that the purified protein is homogeneous and active. The crystal structure revealed a conserved Sm topology, composed of one N-terminal α-helix followed by five twisted β-strands, and a novel π-π stacking intra-subunit interaction of two histidine residues, absent in other Hfq proteins. Moreover, the calculated ab initio envelope based on small-angle X-ray scattering (SAXS) data agreed with the Hfq crystal structure, suggesting that the protein has the same folding structure in solution.
authors.affiliation: Department of Biochemistry and Molecular Biology, Universidade Federal do Paraná, PR, Brazil.
authors.forename: Marco Antonio Seiki
authors.initials: MA
authors.lastname: Kadowaki
authors.forename: Jorge
authors.initials: J
authors.lastname: Iulek
authors.forename: João Alexandre Ribeiro Gonçalves
authors.initials: JA
authors.lastname: Barbosa
authors.forename: Fábio de Oliveira
authors.initials: Fde O
authors.lastname: Pedrosa
authors.forename: Emanuel Maltempi
authors.initials: EM
authors.lastname: de Souza
authors.forename: Leda Satie
authors.initials: LS
authors.lastname: Chubatsu
authors.forename: Rose Adele
authors.initials: RA
authors.lastname: Monteiro
authors.forename: Marco Aurélio Schüler
authors.initials: MA
authors.lastname: de Oliveira
authors.forename: Maria Berenice Reynaud
authors.initials: MB
authors.lastname: Steffens
mesh_terms: D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D018360:Crystallography, X-Ray; D024202:Electrophoretic Mobility Shift Assay; D042803:Herbaspirillum / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry; D035001:Host Factor 1 Protein / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry* / Q000235:genetics; D008969:Molecular Sequence Data; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012313:RNA / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics; D053838:Scattering, Small Angle
chemical_list: D035001:Host Factor 1 Protein; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D006639:Histidine; D012313:RNA