Structural characterization of the type I-B CRISPR Cas7 from Thermobaculum terrenum

• Published in: Biochimica et biophysica acta. Proteins and proteomics Vol. 1871; no. 3; p. 140900
• Main Authors: Seo, Pil-Won, Gu, Do-Heon, Kim, Ji-Won, Kim, Jun-Hong, Park, Suk-Youl, Kim, Jeong-Sun
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.05.2023
• Subjects: Bacteria; Binding Sites; Cas7; Cascade; CRISPR; Csh2; RNA; CRISPR; Csh2; Cas7; Cascade
• ISSN: 1570-9639; 1878-1454
• DOI: 10.1016/j.bbapap.2023.140900

Clustered regularly interspaced short palindromic repeats (CRISPR) in many prokaryotes functions as an adaptive immune system against mobile genetic elements. A heterologous ribonucleoprotein silencing complex composed of CRISPR-associated (Cas) proteins and a CRISPR RNA (crRNA) neutralizes the incoming mobile genetic elements. The type I and III silencing complexes commonly include a protein-helical backbone of several copies of identical subunits, for example, Cas7 in the type I silencing complex. In this study, we structurally characterized type I-B Cas7 (Csh2 from Thermobaculum terrenum; TterCsh2). The revealed crystal structure of TterCsh2 shows a typical glove-like architecture of Cas7, which consists of a palm, a thumb, and a finger domain. Csh2 proteins have 5 conserved sequence motifs that are arranged to form a presumable crRNA-binding site in the TterCsh2 structure. This crRNA binding site of TterCsh2 is structurally and potentially comparable to those observed in helix-forming Cas7 structures in other sub-types. Analysis of the reported Cas7 structures and their sequences suggests that Cas7s can be divided into at least two sub-classes. These data will broaden our understanding on the Cascade complex of CRISPR/Cas systems. •Crystal structure of Cascade backbone-forming type I-B Cas7 (Csh2 from Thermobaculum terrenum; TterCsh2) was determined.•TterCsh2 adopts a typical folding of Cas7.•TterCsh2 is structurally and sequentially more similar to type I-C Cas7 than to those of type I-E and I-F.•Comparative analysis of TterCsh2 with reported Cas7s suggests that Cas7 can be divided into at least two sub-classes.