Structure of a type IV CRISPR-Cas ribonucleoprotein complex

Yi Zhou,Jack P.K Bravo,Hannah N Taylor,Jurre A Steens,Ryan N Jackson,Raymond H.J Staals,David W Taylor

doi:10.1016/j.isci.2021.102201

Yi Zhou, Jack P.K Bravo + Show 5 more

Open Access

https://doi.org/10.1016/j.isci.2021.102201

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Abstract

SummaryWe reveal the cryo-electron microscopy structure of a type IV-B CRISPR ribonucleoprotein (RNP) complex (Csf) at 3.9-Å resolution. The complex best resembles the type III-A CRISPR Csm effector complex, consisting of a Cas7-like (Csf2) filament intertwined with a small subunit (Cas11) filament, but the complex lacks subunits for RNA processing and target DNA cleavage. Surprisingly, instead of assembling around a CRISPR-derived RNA (crRNA), the complex assembles upon heterogeneous RNA of a regular length arranged in a pseudo-A-form configuration. These findings provide a high-resolution glimpse into the assembly and function of enigmatic type IV CRISPR systems, expanding our understanding of class I CRISPR-Cas system architecture, and suggesting a function for type IV-B RNPs that may be distinct from other class 1 CRISPR-associated systems.

Highlights

Bacteria and archaea employ CRISPR (Clustered Regularly Interspaced Short Palindromic Repeat)-Cas (CRISPR-associated) systems for adaptive immunity against phages, plasmids and other mobile-genetic elements (Makarova et al, 2020)
SUMMARY We reveal the cryo-electron microscopy structure of a type IV-B CRISPR ribonucleoprotein (RNP) complex (Csf) at 3.9-Aresolution
Instead of assembling around a CRISPR-derived RNA, the complex assembles upon heterogeneous RNA of a regular length arranged in a pseudo-A-form configuration

Summary

Introduction

Bacteria and archaea employ CRISPR (Clustered Regularly Interspaced Short Palindromic Repeat)-Cas (CRISPR-associated) systems for adaptive immunity against phages, plasmids and other mobile-genetic elements (Makarova et al, 2020). Type IV CRISPR systems primarily occur within plasmid-like elements, lack genes encoding adaptation modules (cas, cas, and cas4), and are classified into three distinct subtypes (IV-A, IV-B, IV-C) (Makarova et al, 2020; Ozcan et al, 2019; Pinilla-Redondo et al, 2019). All type IV systems contain genes that encode for Csf (Cas7), Csf (Cas5), and Csf (large subunit) proteins, which assemble around an RNA to form a multi-subunit complex (Makarova et al, 2020; Ozcan et al, 2019; Pinilla-Redondo et al, 2019).

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