Uncovering New Mechanisms of Type III CRISPR-Cas System Inhibition and Effector Function
type: CreativeWork
description: Bacteria and their viruses, called bacteriophages (phages), are in a constant arms race for survival. Phages are one of the most abundant biological entities in the world, with an estimated 1031on earth, outnumbering bacteria ten to one. To defend against phages, bacteria have evolved numerous defense mechanisms. One such defense system is the bacterial adaptive immune system called CRISPR-Cas, which consists of clustered, regularly interspaced short palindromic repeats (CRISPRs) and a set of genes that encode CRISPR-associated (Cas) proteins. While there are seven distinct types of CRISPR-Cas systems identified thus far, we focus on specifically the type III CRISPR system which contains a multi-protein effector complex that functions together with its crRNA in target binding and cleavage. During type III CRISPR-Cas immunity in prokaryotes, RNA-guided recognition of viral (phage) transcripts stimulates the Cas10 complex to convert ATP into cyclic oligoadenylates. These act as signaling molecules that bind to CRISPR-associated Rossmann Fold (CARF) proteins and activate their effector domains. The effector part unleashes various activities that are toxic to the host cell, inhibiting cell growth and leading to growth arrest. We are now beginning to uncover that CARF effectors use a wide array of mechanisms of action. In the first part of this study, we report the structure and function of the Cap1 effector, composed of a pair of transmembrane helices (TM1/2), a CARF-like (CARFL) domain and a domain of unknown function (DUF4579). Cryo-EM studies on apo-and ligand-bound states of Cap1 in glyco-diosgenin detergent revealed the formation of tetrameric complexes in both states, with one cyclic tetra-adenylate (cA4) molecule bound in a pocket composed by the four CARFL domains. Binding of cA4 triggers conformational changes that widen an otherwise narrow pore formed by the four TM1/2 domains. In vivo, Cap1 activation results in membrane depolarization, a growth arrest of the…
abstract: Bacteria and their viruses, called bacteriophages (phages), are in a constant arms race for survival. Phages are one of the most abundant biological entities in the world, with an estimated 1031on earth, outnumbering bacteria ten to one. To defend against phages, bacteria have evolved numerous defense mechanisms. One such defense system is the bacterial adaptive immune system called CRISPR-Cas, which consists of clustered, regularly interspaced short palindromic repeats (CRISPRs) and a set of genes that encode CRISPR-associated (Cas) proteins. While there are seven distinct types of CRISPR-Cas systems identified thus far, we focus on specifically the type III CRISPR system which contains a multi-protein effector complex that functions together with its crRNA in target binding and cleavage. During type III CRISPR-Cas immunity in prokaryotes, RNA-guided recognition of viral (phage) transcripts stimulates the Cas10 complex to convert ATP into cyclic oligoadenylates. These act as signaling molecules that bind to CRISPR-associated Rossmann Fold (CARF) proteins and activate their effector domains. The effector part unleashes various activities that are toxic to the host cell, inhibiting cell growth and leading to growth arrest. We are now beginning to uncover that CARF effectors use a wide array of mechanisms of action. In the first part of this study, we report the structure and function of the Cap1 effector, composed of a pair of transmembrane helices (TM1/2), a CARF-like (CARFL) domain and a domain of unknown function (DUF4579). Cryo-EM studies on apo-and ligand-bound states of Cap1 in glyco-diosgenin detergent revealed the formation of tetrameric complexes in both states, with one cyclic tetra-adenylate (cA4) molecule bound in a pocket composed by the four CARFL domains. Binding of cA4 triggers conformational changes that widen an otherwise narrow pore formed by the four TM1/2 domains. In vivo, Cap1 activation results in membrane depolarization, a growth arrest of the…
author: Cahir, Clare Wen
keywords: CRISPR-Cas, CARF effector, anti-CRISPRs, Type III, CRISPR-Cas system, Life Sciences
date published: 2026-01-01T08:00:00Z
date modified: 2026-07-24T04:11:55Z
provider: Rockefeller
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Rockefeller