# The NMR structure of the Ea22 lysogenic developmental protein from lambda bacteriophage

## TL;DR

This paper describes the NMR structure of the Ea22 protein's CTD from lambda bacteriophage and suggests it helps promote lysogeny over lytic development.

## Contribution

The study provides the first NMR structure of the Ea22 CTD and identifies structural features unique to lambda phage Ea22.

## Key findings

- The Ea22 CTD has a mixed alpha–beta fold and dimerizes via salt bridges.
- A conserved mobile loop in the CTD may interact with an unknown host protein to promote lysogeny.
- Structural differences in the CTD distinguish lambda Ea22 from Shiga toxin-producing phage homologs.

## Abstract

The ea22 gene resides in a relatively uncharacterized region of the lambda bacteriophage genome between the exo and xis genes and is among the earliest genes transcribed upon infection. In lambda and Shiga toxin-producing phages found in enterohemorrhagic E. coli (EHEC) associated with food poisoning, Ea22 favors a lysogenic over lytic developmental state. The Ea22 protein may be considered in terms of three domains: a short amino-terminal domain, a coiled-coiled domain, and a carboxy-terminal domain (CTD). While the full-length protein is tetrameric, the CTD is dimeric when expressed individually. Here, we report the NMR solution structure of the Ea22 CTD that is described by a mixed alpha–beta fold with a dimer interface reinforced by salt bridges. A conserved mobile loop may serve as a ligand for an unknown host protein that works with Ea22 to promote bacterial survival and the formation of new lysogens. From sequence and structural comparisons, the CTD distinguishes lambda Ea22 from homologs encoded by Shiga toxin-producing bacteriophages.