Relaxase MobM Induces a Molecular Switch at Its Cognate Origin of Transfer.

Fabián Lorenzo-Díaz,Manuel Espinosa,Alicia Bravo,Cris Fernández-López,Beatriz Guillén-Guío

doi:10.3389/fmolb.2018.00017

Abstract

The MOBV1 family of relaxases is broadly distributed in plasmids and other mobile genetic elements isolated from staphylococci, enterococci, and streptococci. The prototype of this family is protein MobM encoded by the streptococcal promiscuous plasmid pMV158. MobM cleaves the phosphodiester bond of a specific dinucleotide within the origin of transfer (oriT) to initiate conjugative transfer. Differently from other relaxases, MobM and probably other members of the family, cleaves its target single-stranded DNA through a histidine residue rather than the commonly used tyrosine. The oriT of the MOBV1 family differs from other well-known conjugative systems since it has sequences with three inverted repeats, which were predicted to generate three mutually-exclusive hairpins on supercoiled DNA. In this work, such hypothesis was evaluated through footprinting experiments on supercoiled plasmid DNA. We have found a change in hairpin extrusion mediated by protein MobM. This conformational change involves a shift from the main hairpin generated on “naked” DNA to a different hairpin in which the nick site is positioned in a single-stranded configuration. Our results indicate that the oriTpMV158 acts as a molecular switch in which, depending on the inverted repeat recognized by MobM, pMV158 mobilization could be turned “on” or “off.”

Highlights

Horizontal Gene Transfer (HGT) is the main source to acquire novel gene traits by organisms
The cleavage reaction generates a covalent amino acyl-DNA adduct that is pumped from donor to recipient cells (Llosa et al, 2002) through a plasmid-encoded multiprotein complex that is composed by the coupling protein and a TypeIV secretion system (Goessweiner-Mohr et al, 2013; Low et al, 2014; Ilangovan et al, 2017; Trokter and Waksman, 2018)
We propose a dynamic model in which a hairpin formed on “naked” DNA changes its conformation upon MobM binding

Summary

Introduction

Horizontal Gene Transfer (HGT) is the main source to acquire novel gene traits by organisms. It is mediated by plasmids and other Mobile Genetic Elements (MGE) that use conjugation as the most frequent process to perform DNA transfer (de la Cruz and Davies, 2000). Conjugation involves physical contact between a donor and a recipient cell, and the process is initiated and terminated by dedicated topoisomerase endonuclease-like proteins termed relaxases (de la Cruz and Davies, 2000; Chandler et al, 2013; Lorenzo-Díaz et al, 2016). The cleavage reaction generates a covalent amino acyl-DNA adduct that is pumped from donor to recipient cells (Llosa et al, 2002) through a plasmid-encoded multiprotein complex that is composed by the coupling protein and a TypeIV secretion system (Goessweiner-Mohr et al, 2013; Low et al, 2014; Ilangovan et al, 2017; Trokter and Waksman, 2018)

Methods

Results

Conclusion