PglZ from Type I BREX phage defence systems is a metal-dependent nuclease that forms a sub-complex with BrxB

Readshaw, J.; Doyle, L.; Puiu, M.; Kelly, A.; Nelson, A.; Kaiser, A.; McGuire, S.; Peralata-Acosta, J.; Smith, D.; Stoddard, B. L.; Kaiser, B. K.; Blower, T. R.

doi:10.1101/2025.03.26.645558

bioRxiv · 10.1101/2025.03.26.645558

PglZ from Type I BREX phage defence systems is a metal-dependent nuclease that forms a sub-complex with BrxB

Readshaw, J.·Doyle, L.·Puiu, M.·Kelly, A.·Nelson, A.·Kaiser, A.·McGuire, S.·Peralata-Acosta, J.·Smith, D.·Stoddard, B. L.·Kaiser, B. K.·Blower, T. R.

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Abstract

BREX (Bacteriophage Exclusion) systems, identified through shared identity with Pgl (Phage Growth Limitation) systems, are a widespread, highly diverse group of phage defence systems found throughout bacteria and archaea. The varied BREX Types harbour multiple protein subunits (between four and eight) and all encode a conserved putative phosphatase (PglZ aka BrxZ) and an equally conserved, putative ATPase (BrxC). Almost all BREX systems also contain a site-specific methyltransferase (PglX aka BrxX). Despite having determined the structure and fundamental biophysical and biochemical behaviours for the PglX methyltransferase, the BrxL effector, the BrxA DNA-binding protein and the BrxR transcriptional regulator, the mechanism by which BREX impedes phage replication remains largely undetermined. In this study, we identify a stable BREX sub-complex of PglZ:BrxB, validate the structure and dynamic behaviour of that sub-complex, and assess the biochemical activity of PglZ, revealing it to be a metal-dependent nuclease. PglZ can cleave cyclic oligonucleotides, linear oligonucleotides, plasmid DNA and both non-modified and modified linear phage genomes. PglZ nuclease activity has no obvious role in BREX-dependent methylation, but does contribute to BREX phage defence. BrxB binding does not impact PglZ nuclease activity. These data contribute to our growing understanding of the BREX phage defence mechanism.

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Readshaw, J., Doyle, L., Puiu, M., Kelly, A., Nelson, A., Kaiser, A., McGuire, S., Peralata-Acosta, J., Smith, D., Stoddard, B. L., Kaiser, B. K., Blower, T. R.. 2025-03-26. PglZ from Type I BREX phage defence systems is a metal-dependent nuclease that forms a sub-complex with BrxB. https://doi.org/10.1101/2025.03.26.645558

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