Identifying the region responsible for Brucella abortus MucR higher-order oligomer formation and examining its role in gene regulation

Luciano Pirone,Roberto Fattorusso,Gaetano Malgieri,Emilia Maria Pedone,Joshua Edison Pitzer,Gianluca D’Abrosca,Ilaria Baglivo,Paolo Vincenzo Pedone,Roy Martin Roop

doi:10.1038/s41598-018-35432-1

Abstract

MucR is a member of the Ros/MucR family of prokaryotic zinc-finger proteins found in the α-proteobacteria which regulate the expression of genes required for the successful pathogenic and symbiotic interactions of these bacteria with the eukaryotic hosts. The structure and function of their distinctive zinc-finger domain has been well-studied, but only recently the quaternary structure of the full length proteins was investigated demonstrating their ability to form higher-order oligomers. The aim of this study was to identify the region of MucR involved in higher-order oligomer formation by analysing deletion and point mutants of this protein by Light Scattering, and to determine the role that MucR oligomerization plays in the regulatory function of this protein. Here we demonstrate that a conserved hydrophobic region at the N-terminus of MucR is responsible for higher-order oligomer formation and that MucR oligomerization is essential for its regulatory function in Brucella. All these features of MucR are shared by the histone-like nucleoid structuring protein, (H-NS), leading us to propose that the prokaryotic zinc-finger proteins in the MucR/Ros family control gene expression employing a mechanism similar to that used by the H-NS proteins, rather than working as classical transcriptional regulators.

Highlights

The Ros/MucR protein family[1,2] includes prokaryotic zinc-finger proteins such as Ros from Agrobacterium tumefaciens[3] and MucR from Brucella spp.[4,5,6], both of which regulate genes required for the virulence of these strains in their respective plant and animal hosts[2,5,6,7]
H-NS proteins play important roles in nucleoid compaction, but they serve as gene silencers, preventing the potentially toxic expression of bacterial genes acquired by horizontal gene transfer[35,36,37] and repressing the gratuitous expression of virulence genes in bacterial pathogens[38,39]
Based on the results presented here, together with previously published findings[26,27], we propose that the prokaryotic zinc-finger proteins in the Ros/MucR family control gene expression by employing a mechanism similar to that used by the H-NS proteins, rather than working as classical transcriptional regulators

Summary

Introduction

The Ros/MucR protein family[1,2] includes prokaryotic zinc-finger proteins such as Ros from Agrobacterium tumefaciens[3] and MucR from Brucella spp.[4,5,6], both of which regulate genes required for the virulence of these strains in their respective plant and animal hosts[2,5,6,7]. One of the important features of H-NS proteins with regard to their ability to serve as gene silencers is their capacity to recognize AT-rich DNA-target sites containing T-A steps in and around promoters. They use these sequences as nucleation sites to form higher-order oligomers that prevent RNA polymerase access to these promoters[40,41]. Based on the results presented here, together with previously published findings[26,27], we propose that the prokaryotic zinc-finger proteins in the Ros/MucR family control gene expression by employing a mechanism similar to that used by the H-NS proteins, rather than working as classical transcriptional regulators

Objectives

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Results

Discussion

Conclusion