title: Three-dimensional structures of fibrillar Sm proteins: Hfq and other Sm-like proteins.
abstract: Hfq is a nucleic acid-binding protein that functions as a global regulator of gene expression by virtue of its interactions with several small, non-coding RNA species. Originally identified as an Escherichia coli host factor required for RNA phage Qbeta replication, Hfq is now known to post-transcriptionally regulate bacterial gene expression by modulating both mRNA stability and translational activity. Recently shown to be a member of the diverse Sm protein family, Hfq adopts the OB-like fold typical of other Sm and Sm-like (Lsm) proteins, and also assembles into toroidal homo-oligomers that bind single-stranded RNA. Similarities between the structures, functions, and evolution of Sm/Lsm proteins and Hfq are continually being discovered, and we now report an additional, unexpected biophysical property that is shared by Hfq and other Sm proteins: E.coli Hfq polymerizes into well-ordered fibres whose morphologies closely resemble those found for Sm-like archaeal proteins (SmAPs). However, the hierarchical assembly of these fibres is dissimilar: whereas SmAPs polymerize into polar tubes (and striated bundles of such tubes) by head-to-tail stacking of individual homo-heptamers, helical Hfq fibres are formed by cylindrical slab-like layers that consist of 36 subunits arranged as a hexamer of Hfq homo-hexamers (i.e. protofilaments in a 6 x 6 arrangement). The different fibrillar ultrastructures formed by Hfq and SmAP are presented and examined herein, with the overall goal of elucidating another similarity amongst the diverse members of the Sm protein family.
authors.affiliation: Institut de Biologie Physico-Chimique, CNRS UPR 9073 conventionnée avec l'université Paris 7, 13 rue P. et M. Curie, 75005 Paris, France. veronique.arlusion@ibpc.fr
authors.forename: Véronique
authors.initials: V
authors.lastname: Arluison
authors.forename: Cameron
authors.initials: C
authors.lastname: Mura
authors.forename: Maria Romero
authors.initials: MR
authors.lastname: Guzmán
authors.forename: Jean
authors.initials: J
authors.lastname: Liquier
authors.forename: Olivier
authors.initials: O
authors.lastname: Pellegrini
authors.forename: Mari
authors.initials: M
authors.lastname: Gingery
authors.forename: Philippe
authors.initials: P
authors.lastname: Régnier
authors.forename: Sergio
authors.initials: S
authors.lastname: Marco
mesh_terms: D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D035001:Host Factor 1 Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D021621:Imaging, Three-Dimensional; D017014:Methanobacterium / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D019843:Archaeal Proteins; D029968:Escherichia coli Proteins; C087373:Hfq protein, E coli; D035001:Host Factor 1 Protein