Structure-function analysis of MmpL7-mediated lipid transport in mycobacteria

Nabiela Moolla,Rebeca Bailo,Robert Marshall,Vassiliy N Bavro,Apoorva Bhatt

doi:10.1016/j.tcsw.2021.100062

Nabiela Moolla, Rebeca Bailo + Show 3 more

Open Access

https://doi.org/10.1016/j.tcsw.2021.100062

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Journal: The Cell Surface	Publication Date: Aug 31, 2021
Citations: 3	License type: cc-by

Affiliation: University of Birmingham, University of Essex

Abstract

Mycobacterial membrane protein Large (MmpL7) is a Resistance-Nodulation-Division (RND) family transporter required for the export of the virulence lipid, phthiocerol dimycocerosate (PDIM), in Mycobacterium tuberculosis. Using a null mutant of the related, vaccine strain Mycobacterium bovis BCG, we show that MmpL7 is also involved in the transport of the structurally related phenolic glycolipid (PGL), which is also produced by the hypervirulent M. tuberculosis strain HN878, but absent in M. tuberculosis H37Rv. Furthermore, we generated an in silico model of M. tuberculosis MmpL7 that revealed MmpL7 as a functional outlier within the MmpL-family, missing a canonical proton-relay signature sequence, suggesting that it employs a yet-unidentified mechanism for energy coupling for transport. In addition, our analysis demonstrates that the periplasmic porter domain 2 insert (PD2-insert), which doesn't share any recognisable homology, is highly alpha-helical in nature, suggesting an organisation similar to that seen in the hopanoid PD3/4 domains. Using the M. bovis BCG mmpL7 mutant for functional complementation with mutated alleles of mmpL7, we were able to identify residues present in the transmembrane domains TM4 and TM10, and the PD2 domain insert that play a crucial role in PDIM transport, and in certain cases, biosynthesis of PDIM.

Highlights

The cell envelopes of mycobacteria, including the tuberculosiscausing Mycobacterium tuberculosis, are rich in unique lipids that form a hydrophobic barrier, playing a role in resistance and virulence (Jan kute et al, 2015; Gago et al, 2018; Garcia-Vilanova et al, 2019).Two M. tuberculosis cell envelope lipids, phthiocerol dimycocerosate (PDIM) and phenolic glycolipid (PGL) play an important role in viru lence
intracellular lipids (In) M. tuberculosis the mmpL7 (Rv2942) gene is located in the PDIM/ PGL biosynthesis cluster (Onwueme et al, 2005) (Fig. 1)
The PD2 of M. tuberculosis MmpL7 has been shown to interact with the phthiocerol-producing PpsE, suggesting that biosynthesis of PDIM may be coupled with its transport (Jain and Cox, 2005)

Summary

Introduction

The cell envelopes of mycobacteria, including the tuberculosiscausing Mycobacterium tuberculosis, are rich in unique lipids that form a hydrophobic barrier, playing a role in resistance and virulence (Jan kute et al, 2015; Gago et al, 2018; Garcia-Vilanova et al, 2019).Two M. tuberculosis cell envelope lipids, phthiocerol dimycocerosate (PDIM) and phenolic glycolipid (PGL) play an important role in viru lence. In M. tuberculosis the mmpL7 (Rv2942) gene is located in the PDIM/ PGL biosynthesis cluster (Onwueme et al, 2005) (Fig. 1).

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