MmpA, a Conserved Membrane Protein Required for Efficient Surface Transport of Trehalose Lipids in Corynebacterineae.

Tamaryn J Cashmore,Ross L Coppel,Arek K Rainczuk,Malcolm J Mcconville,Paul K Crellin,Stephan Klatt,Rajini Brammananth

doi:10.3390/biom11121760

Abstract

Cell walls of bacteria of the genera Mycobacterium and Corynebacterium contain high levels of (coryno)mycolic acids. These very long chain fatty acids are synthesized on the cytoplasmic leaflet of the inner membrane (IM) prior to conjugation to the disaccharide, trehalose, and transport to the periplasm. Recent studies on Corynebacterium glutamicum have shown that acetylation of trehalose monohydroxycorynomycolate (hTMCM) promotes its transport across the inner membrane. Acetylation is mediated by the membrane acetyltransferase, TmaT, and is dependent on the presence of a putative methyltransferase, MtrP. Here, we identify a third protein that is required for the acetylation and membrane transport of hTMCM. Deletion of the C. glutamicum gene NCgl2761 (Rv0226c in Mycobacterium tuberculosis) abolished synthesis of acetylated hTMCM (AcTMCM), resulting in an accumulation of hTMCM in the inner membrane and reduced synthesis of trehalose dihydroxycorynomycolate (h2TDCM), a major outer membrane glycolipid. Complementation with the NCgl2761 gene, designated here as mmpA, restored the hTMCM:h2TDCM ratio. Comprehensive lipidomic analysis of the ΔtmaT, ΔmtrP and ΔmmpA mutants revealed strikingly similar global changes in overall membrane lipid composition. Our findings suggest that the acetylation and membrane transport of hTMCM is regulated by multiple proteins: MmpA, MtrP and TmaT, and that defects in this process lead to global, potentially compensatory changes in the composition of inner and outer membranes.

Highlights

We recently showed that the hydroxylated corynomycolate chain in C. glutamicum, trehalose monocorynomycolate, is transiently modified with an acetyl group and that this modification is important for periplasmic transport of TMCM
We have previously identified a gene locus that is highly conserved in mycobacteria and corynebacteria and is important for cell wall synthesis (Figure 1A)
We show that C. glutamicum NCgl2761, designated here as MmpA, is required for the synthesis of acetylated hTMCM (AcTMCM) and transport of TMCM species across the inner membrane (IM)

Summary

Introduction

Bacteria of the genera Mycobacterium and Corynebacterium comprise the suborder Corynebacterineae and cause severe human diseases such as tuberculosis (Mycobacterium tuberculosis), leprosy (Mycobacterium leprae) and diphtheria (Corynebacterium diphtheriae). M. tuberculosis latently infects around one-quarter of the human population, resulting in ~1.4 million deaths annually from tuberculosis (TB) [1]. Around ten million people contracted TB in 2019, mostly in Southeast Asia, Africa and the Western Pacific region. While the incidence of TB has been gradually falling, the prevalence of drug resistant strains of M. tuberculosis, rifampicin-resistant (RR-TB) and multi-drug resistant (MDR-TB) strains, is increasing and represents a significant threat.

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