Work

Structural insights into the assembly and function of Retron Ec78 PtuAB

Year: 2026

Type: article

Abstract: The Retron system is a crucial prokaryotic anti-phage defense mechanism, composed of a noncoding RNA, reverse transcriptase, and effector proteins, which synthesizes multicopy single-stranded DNA to trigger immune responses. While Retron Ec86’s anti-phage mechanism has been elucidated, other Retron types remain poorly understood. Here, we investigate Retron Ec78, a Type I-A system encoding effector proteins PtuA (ATPase) and PtuB (HNH nuclease). Structural analysis reveals that PtuA hexameric complex putatively bound to PtuB, with ATP playing a key role in hexamer assembly. Beyond its known role in abortive infection via tRNA degradation, we demonstrate that the PtuAB complex also exhibits DNA-cleaving activity. These findings provide novel insights into the assembly and dual functionality of the Retron Ec78 system, advancing our understanding of prokaryotic immune mechanisms against phage infection. This study reports the cryo-EM structure of a Type I-A prokaryotic anti-phage defense mechanism, Retron Ec78, and in particular of the PtuA hexameric ATPase putatively bound to the PtuB nuclease. Beyond its known role in abortive infection via tRNA degradation, the authors demonstrate that the PtuAB complex also exhibits DNA-cleaving activity.

Source: Communications Biology

DOI: 10.1038/s42003-026-10199-8