title: Structure and RNA-binding properties of the type III-A CRISPR-associated protein Csm3.
abstract: The prokaryotic adaptive immune system is based on the incorporation of genome fragments of invading viral genetic elements into clusters of regulatory interspaced short palindromic repeats (CRISPRs). The CRISPR loci are transcribed and processed into crRNAs, which are then used to target the invading nucleic acid for degradation. The large family of CRISPR-associated (Cas) proteins mediates this interference response. We have characterized Methanopyrus kandleri Csm3, a protein of the type III-A CRISPR-Cas complex. The 2.4 Å resolution crystal structure shows an elaborate four-domain fold organized around a core RRM-like domain. The overall architecture highlights the structural homology to Cas7, the Cas protein that forms the backbone of type I interference complexes. Csm3 binds unstructured RNAs in a sequence non-specific manner, suggesting that it interacts with the variable spacer sequence of the crRNA. The structural and biochemical data provide insights into the similarities and differences in this group of Cas proteins.
authors.affiliation: Structural Cell Biology Department; Max Planck Institute of Biochemistry; Munich/Martinsried, Germany.
authors.forename: Ajla
authors.initials: A
authors.lastname: Hrle
authors.affiliation: Max Planck Institute for Terrestrial Microbiology; Karl-von-Frisch-Straße 10, Marburg, Germany.
authors.forename: Andreas A H
authors.initials: AA
authors.lastname: Su
authors.affiliation: Structural Cell Biology Department; Max Planck Institute of Biochemistry; Munich/Martinsried, Germany.
authors.forename: Judith
authors.initials: J
authors.lastname: Ebert
authors.affiliation: Structural Cell Biology Department; Max Planck Institute of Biochemistry; Munich/Martinsried, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Benda
authors.affiliation: Max Planck Institute for Terrestrial Microbiology; Karl-von-Frisch-Straße 10, Marburg, Germany.
authors.forename: Lennart
authors.initials: L
authors.lastname: Randau
authors.affiliation: Structural Cell Biology Department; Max Planck Institute of Biochemistry; Munich/Martinsried, Germany.
authors.forename: Elena
authors.initials: E
authors.lastname: Conti
mesh_terms: D000595:Amino Acid Sequence; D019843:Archaeal Proteins / Q000737:chemistry* / Q000378:metabolism; D064130:CRISPR-Associated Proteins / Q000737:chemistry* / Q000378:metabolism; D019605:Euryarchaeota / Q000378:metabolism*; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D017354:Point Mutation; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D019642:RNA, Archaeal / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D019843:Archaeal Proteins; D064130:CRISPR-Associated Proteins; D019642:RNA, Archaeal; D016601:RNA-Binding Proteins
keywords: Cas7; RAMP; RRM domain; adaptive immunity; ferredoxin domain