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Mechanistic insight into mycobacterial MmpL protein function
1Ecole Polytechnique Fédérale de Lausanne, Global Health Institute, CH1015, Lausanne, Switzerland.
Abstract:
Mycobacterial cell walls are complex structures containing a broad range of unusual lipids, glycolipids and other polymers, some of which act as immunomodulators or virulence determinants. Better understanding of the enzymes involved in export processes would enlighten cell wall biogenesis. Bernut et al. () present the findings of a structural and functional investigation of one of the most important transporter families, the MmpL proteins, members of the resistance-nodulation-cell division (RND) superfamily. A Tyr842His missense mutation in the mmpL4a gene was shown to be responsible for the smooth-to-rough morphotype change of the near untreatable opportunistic pathogen Mycobacterium bolletii due to its failure to export a glycopeptidolipid (GPL). This mutation was pleiotropic and markedly increased virulence in infection models. Tyr842 is well conserved in all actinobacterial MmpL proteins suggesting that it is functionally important and this was confirmed by several approaches including replacing the corresponding residue in MmpL3 of Mycobacterium tuberculosis. Structural modelling combined with experimental results showed Tyr842 to be a critical residue for mediating the proton motive force required for GPL export. This mechanistic insight applies to all MmpL proteins and probably to all RND transporters.
Insights
A mutation in the MmpL4a transporter of Mycobacterium bolletii prevents glycopeptidolipid export, altering cell wall structure and increasing virulence. This finding reveals a critical residue for transporter function and has implications for understanding mycobacterial cell wall biogenesis.
Area of Science:
- Microbiology
- Structural Biology
- Biochemistry
Background:
- Mycobacterial cell walls possess complex lipid structures influencing virulence.
- Understanding lipid export mechanisms is crucial for cell wall biogenesis research.
Purpose of the Study:
- Investigate the structure and function of MmpL proteins, key transporters in the resistance-nodulation-cell division (RND) superfamily.
- Elucidate the role of a specific mutation in the mmpL4a gene of Mycobacterium bolletii on glycopeptidolipid export and virulence.
Main Methods:
- Structural and functional investigation of MmpL proteins.
- Site-directed mutagenesis (Tyr842His in mmpL4a) and cross-species residue replacement (MmpL3 in Mycobacterium tuberculosis).
- Structural modeling and experimental validation.
Main Results:
- A Tyr842His mutation in mmpL4a caused a failure in glycopeptidolipid (GPL) export, leading to a smooth-to-rough morphotype change in Mycobacterium bolletii.
- This mutation significantly increased pathogen virulence in infection models.
- Tyr842 was identified as a critical residue for mediating the proton motive force essential for GPL export, a finding conserved across MmpL proteins.
Conclusions:
- The study identifies a critical functional residue (Tyr842) in MmpL transporters essential for lipid export and virulence.
- Mechanistic insights into MmpL4a function provide a broader understanding applicable to MmpL family and RND transporters.
- Findings contribute to understanding mycobacterial cell wall biogenesis and potential therapeutic targets.
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