title: Crystal structure of a heptameric Sm-like protein complex from archaea: implications for the structure and evolution of snRNPs.
abstract: The Sm/Lsm proteins associate with small nuclear RNA to form the core of small nuclear ribonucleoproteins, required for processes as diverse as pre-mRNA splicing, mRNA degradation and telomere formation. The Lsm proteins from archaea are likely to represent the ancestral Sm/Lsm domain. Here, we present the crystal structure of the Lsm alpha protein from the thermophilic archaeon Methanobacterium thermoautotrophicum at 2.0 A resolution. The Lsm alpha protein crystallizes as a heptameric ring comprised of seven identical subunits interacting via beta-strand pairing and hydrophobic interactions. The heptamer can be viewed as a propeller-like structure in which each blade consists of a seven-stranded antiparallel beta-sheet formed from neighbouring subunits. There are seven slots on the inner surface of the heptamer ring, each of which is lined by Asp, Asn and Arg residues that are highly conserved in the Sm/Lsm sequences. These conserved slots are likely to form the RNA-binding site. In archaea, the gene encoding Lsm alpha is located next to the L37e ribosomal protein gene in a putative operon, suggesting a role for the Lsm alpha complex in ribosome function or biogenesis.
authors.affiliation: Department of Chemistry, Macquarie University, NSW 2109, Australia.
authors.forename: B M
authors.initials: BM
authors.lastname: Collins
authors.forename: S J
authors.initials: SJ
authors.lastname: Harrop
authors.forename: G D
authors.initials: GD
authors.lastname: Kornfeld
authors.forename: I W
authors.initials: IW
authors.lastname: Dawes
authors.forename: P M
authors.initials: PM
authors.lastname: Curmi
authors.forename: B C
authors.initials: BC
authors.lastname: Mabbutt
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D019143:Evolution, Molecular; D023061:Gene Order; D006860:Hydrogen Bonding; D017014:Methanobacterium / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D012313:RNA / Q000235:genetics / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012269:Ribosomal Proteins / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D019843:Archaeal Proteins; D021122:Protein Subunits; D017411:Ribonucleoproteins, Small Nuclear; D012269:Ribosomal Proteins; D012313:RNA