title: Crystal structure of the Csm3-Csm4 subcomplex in the type III-A CRISPR-Cas interference complex.
abstract: Clustered, regularly interspaced, short palindromic repeat (CRISPR) loci play a pivotal role in the prokaryotic host defense system against invading genetic materials. The CRISPR loci are transcribed to produce CRISPR RNAs (crRNAs), which form interference complexes with CRISPR-associated (Cas) proteins to target the invading nucleic acid for degradation. The interference complex of the type III-A CRISPR-Cas system is composed of five Cas proteins (Csm1-Csm5) and a crRNA, and targets invading DNA. Here, we show that the Csm1, Csm3, and Csm4 proteins from Methanocaldococcus jannaschii form a stable subcomplex. We also report the crystal structure of the M. jannaschii Csm3-Csm4 subcomplex at 3.1Å resolution. The complex structure revealed the presence of a basic concave surface around their interface, suggesting the RNA and/or DNA binding ability of the complex. A gel retardation analysis showed that the Csm3-Csm4 complex binds single-stranded RNA in a non-sequence-specific manner. Csm4 structurally resembles Cmr3, a component of the type III-B CRISPR-Cas interference complex. Based on bioinformatics, we constructed a model structure of the Csm1-Csm4-Csm3 ternary complex, which provides insights into its role in the Csm interference complex.
authors.affiliation: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba-shi, Ibaraki 305-8566, Japan. Electronic address: t-numata@aist.go.jp.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Numata
authors.affiliation: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba-shi, Ibaraki 305-8566, Japan.
authors.forename: Hideko
authors.initials: H
authors.lastname: Inanaga
authors.affiliation: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba-shi, Ibaraki 305-8566, Japan.
authors.forename: Chikara
authors.initials: C
authors.lastname: Sato
authors.affiliation: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba-shi, Ibaraki 305-8566, Japan.
authors.forename: Takuo
authors.initials: T
authors.lastname: Osawa
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics; D064130:CRISPR-Associated Proteins / Q000737:chemistry* / Q000235:genetics; D064112:Clustered Regularly Interspaced Short Palindromic Repeats / Q000235:genetics*; D056426:Genetic Loci; D063747:Methanocaldococcus / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011487:Protein Conformation; D012329:RNA, Bacterial / Q000235:genetics; D014961:X-Ray Diffraction
chemical_list: D001426:Bacterial Proteins; D064130:CRISPR-Associated Proteins; D012329:RNA, Bacterial
keywords: CRISPR; Cas; Csm complex; RNA-based defense system; crRNA