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Updated: Jan 15, 2026
Analysis of the Lipid Composition of Mycobacteria by Thin Layer Chromatography
Published on: April 16, 2021
MmpL12 transports lipooligosaccharides and impacts virulence in Mycobacterium marinum
Rebeca Bailo1, C M Santosh Kumar1, Albel Singh1
1School of Biosciences and Institute of Microbiology and Infection, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
Abstract:
Lipooligosaccharides (LOSs) are polar glycolipids found in the cell envelope of many pathogenic mycobacteria. Here, we show that LOS transport in Mycobacterium marinum requires mmpL12, a member of the resistance-nodulation-division family of membrane proteins. Deletion of mmpL12 resulted in a rough colony morphology and increased hydrophobicity. The △mmpL12 mutant accumulated three of the biosynthesis intermediates of LOSs (LOS-I, LOS-II and LOS-III) intracellularly and failed to produce the final product, LOS-IV, suggesting that final glycosylation of LOS-III to yield LOS-IV occurs extracellularly after LOS-III export. In silico structural analysis of the MmpL12 suggests that it is a proton-driven transporter that shares very similar organization with other subclass 1 MmpLs (MmpL1, 2, 4-8 and 9-10), featuring a large periplasmic loop (PD3 domain) which is predicted to form a large coiled coil that may be involved in the trimerization of this subset of MmpL transporters. Furthermore, the long C-terminal extension domain, which is unique to MmpL12, may provide additional trimerization support and scaffold for assembly of additional LOS biosynthetic enzymes. The absence of any extracellular LOS intermediates and of LOS-IV had an impact on virulence, with the mutant strain exhibiting a larger bacterial burden in infected zebrafish embryos.
Insights
Mycobacterium marinum requires the mmpL12 gene for transporting lipooligosaccharides (LOSs). Deleting mmpL12 disrupts LOS production and impacts virulence in zebrafish.
Area of Science:
- Microbiology
- Molecular Biology
- Glycobiology
Background:
- Lipooligosaccharides (LOSs) are crucial polar glycolipids in the cell envelope of pathogenic mycobacteria.
- Understanding LOS transport is vital for deciphering mycobacterial pathogenesis.
Purpose of the Study:
- To investigate the role of the mmpL12 gene in lipooligosaccharide (LOS) transport in *Mycobacterium marinum*.
- To elucidate the function of MmpL12 in LOS biosynthesis and its impact on bacterial virulence.
Main Methods:
- Gene deletion of *mmpL12* in *Mycobacterium marinum*.
- Analysis of colony morphology and cell envelope hydrophobicity.
- Intracellular and extracellular detection of LOS intermediates and final products using biochemical assays.
- *In silico* structural analysis of the MmpL12 protein.
- Assessment of bacterial burden in a zebrafish embryo infection model.
Main Results:
- Deletion of *mmpL12* resulted in rough colony morphology and increased hydrophobicity.
- The *mmpL12* deletion mutant accumulated LOS biosynthesis intermediates intracellularly and failed to produce mature LOS.
- Structural analysis predicted MmpL12 as a proton-driven transporter potentially involved in trimerization and scaffolding LOS biosynthetic enzymes.
- The absence of extracellular LOS and LOS-IV in the mutant impaired virulence, leading to increased bacterial burden in zebrafish embryos.
Conclusions:
- MmpL12 is essential for the transport of lipooligosaccharides in *Mycobacterium marinum*.
- MmpL12 function is critical for proper LOS assembly and export, influencing bacterial virulence.
- MmpL12's unique structural features suggest a role in coordinating LOS biosynthesis and transport.
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