Novel anti-repression mechanism of H-NS proteins by a phage protein.

Fredj Ben Bdira,Simon L Dove,Remus T Dame,Marcellus Ubbink,Nicholas Bowring,Liang Qin,Alexander N Volkov,Andrew M Lippa,Amanda M Erkelens,Aimee L Boyle

doi:10.1093/nar/gkab793

Abstract

H-NS family proteins, bacterial xenogeneic silencers, play central roles in genome organization and in the regulation of foreign genes. It is thought that gene repression is directly dependent on the DNA binding modes of H-NS family proteins. These proteins form lateral protofilaments along DNA. Under specific environmental conditions they switch to bridging two DNA duplexes. This switching is a direct effect of environmental conditions on electrostatic interactions between the oppositely charged DNA binding and N-terminal domains of H-NS proteins. The Pseudomonas lytic phage LUZ24 encodes the protein gp4, which modulates the DNA binding and function of the H-NS family protein MvaT of Pseudomonas aeruginosa. However, the mechanism by which gp4 affects MvaT activity remains elusive. In this study, we show that gp4 specifically interferes with the formation and stability of the bridged MvaT–DNA complex. Structural investigations suggest that gp4 acts as an ‘electrostatic zipper’ between the oppositely charged domains of MvaT protomers, and stabilizes a structure resembling their ‘half-open’ conformation, resulting in relief of gene silencing and adverse effects on P. aeruginosa growth. The ability to control H-NS conformation and thereby its impact on global gene regulation and growth might open new avenues to fight Pseudomonas multidrug resistance.

Highlights

Bacteriophages––viruses that infect bacteria - are among the most abundant and diverse organisms on earth [1,2] and are found wherever bacteria exist
Previous studies have suggested that the LUZ24 gp4 protein negatively affects Pseudomonas growth by targeting its H-NS family protein, MvaT2 sample in the presence of gp4 (MvaT) [36]
These results suggest a loss of the intermolecular interaction between gp4 K42E/K45E and the DNA binding domain (DBD)-linker of the MvaT2. These data support our model in which gp4 is acting as an electrostatic stabilizer of a structure resembling the ‘half-open’ state of the MvaT protomers for the selective inhibition of their DNA bridging activity. Bacterial species and their associated bacteriophages are in a relentless evolutionary arms race in which they develop defense and counter-defense mechanisms to assure survival

Summary

Introduction

Bacteriophages––viruses that infect bacteria - are among the most abundant and diverse organisms on earth [1,2] and are found wherever bacteria exist. Bacterial xenogeneic silencers play essential roles in bacterial evolution by recognizing and silencing foreign genes acquired through horizontal gene transfer [9,10], resulting from transformation, conjugation, or transduction The silencing of these foreign genes, up to the moment that their expression is induced following an environmental cue, can provide bacteria with a competitive advantage under specific conditions without compromising global genome regulation [11]. Characteristic of H-NS family proteins is the formation of nucleofilaments along the DNA that can switch to mediate DNA–DNA bridges in response to environmental changes [18,19,20,21,22,23] This interchange between the DNA binding modes of H-NS family proteins is thought to play an important role in the global regulation

Methods

Results

Conclusion