Preprint: high-throughput screen characterises hundreds of anti-CRISPR protein homologues in eukaryotic cells

A preprint posted to bioRxiv describes a high-throughput screening platform designed to characterise anti-CRISPR (Acr) proteins — naturally occurring inhibitors of CRISPR systems — in eukaryotic cells. The researchers tested hundreds of Acr homologues against two Cas9 variants widely used in research and therapeutic applications: SpyCas9 (derived from Streptococcus pyogenes) and SauCas9 (from Staphylococcus aureus).

Bacteria evolved CRISPR systems as defences against mobile genetic elements such as bacteriophages. In response, some mobile genetic elements encode Acr proteins that counteract CRISPR activity. These proteins have attracted interest as potential regulators of Cas9 activity in biotechnological and therapeutic gene-editing contexts, where the ability to switch off or fine-tune CRISPR activity after delivery could be beneficial.

The screen characterised the inhibitory potency of hundreds of Acr homologues and explored evolutionary patterns across Acr protein families, including proteins that lack obvious sequence similarity to previously described protein families. The authors note that activity profiles varied considerably across homologues, even within related families.

This work has not yet been peer-reviewed. It represents a resource-generation effort that may inform future efforts to deploy Acr proteins as controllable regulators of CRISPR-based gene editing.