The envelope of mycobacteria

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Mycobacteria, responsible for tuberculosis and leprosy, exhibit remarkable resistance to antimicrobial agents.
• This resistance is largely attributed to their unique cell wall structure, characterized by low permeability.
• Key components include mycolic acids, arabinogalactan, and various extractable lipids.

Purpose of the Study:

• To elucidate the structural basis of mycobacterial cell wall permeability.
• To understand how cell wall composition influences the susceptibility of mycobacteria to therapeutic agents.
• To explore the role of mycolic acid structure in modulating cell wall properties.

Main Methods:

• Analysis of mycobacterial cell wall lipid structures, including trehalose-based lipooligosaccharides, phenolic glycolipids, and glycopeptidolipids.
• Structural elucidation of arabinogalactan.
• Investigating the assembly of lipid hydrocarbon chains into asymmetric bilayers.
• Considering the role of porins in nutrient and inhibitor transport.

Main Results:

• Mycobacterial cell walls feature a thick, asymmetric lipid bilayer formed by assembled hydrocarbon chains.
• Cell wall fluidity varies, being lowest internally and increasing towards the exterior.
• Differences in mycolic acid structure correlate with variations in cell wall fluidity, permeability, and susceptibility to lipophilic inhibitors.
• Porins facilitate the passage of hydrophilic molecules.

Conclusions:

• The unique structural organization of the mycobacterial cell wall, particularly the lipid bilayer and mycolic acid variations, dictates its low permeability and contributes to drug resistance.
• Understanding these structural-functional relationships is crucial for developing effective anti-mycobacterial therapies.
• Porins represent a distinct pathway for hydrophilic substance transport across the mycobacterial cell wall.