The cell walls of mycobacteria form an exceptional permeability barrier, and they are essential for virulence. They contain extractable lipids and long-chain mycolic acids that are covalently linked to peptidoglycan via an arabinogalactan network. The lipids were thought to form an asymmetrical bilayer of considerable thickness, but this could never be proven directly by microscopy or other means. Cryo-electron tomography of unperturbed or detergent-treated cells of Mycobacterium smegmatis embedded in vitreous ice now reveals the native organization of the cell envelope and its delineation into several distinct layers. The 3D data and the investigation of ultrathin frozen-hydrated cryosections of M. smegmatis, Myobacterium bovis bacillus Calmette–Guerin, and Corynebacterium glutamicum identified the outermost layer as a morphologically symmetrical lipid bilayer. The structure of the mycobacterial outer membrane necessitates considerable revision of the current view of its architecture. Conceivable models are proposed and discussed. These results are crucial for the investigation and understanding of transport processes across the mycobacterial cell wall, and they are of particular medical relevance in the case of pathogenic mycobacteria.

https://www.pnas.org/content/pnas/105/10/3963.full.pdf

Disclosure of the mycobacterial outer membrane: cryo-electron tomography and vitreous sections reveal the lipid bilayer structure.

https://www.cell.com/trends/microbiology/pdf/S0966-842X(09)00261-3.pdf

Mycobacterial outer membranes: in search of proteins.

Clofazimine (CFZ), an antibacterial and anti-inflammatory drug, is also recommended by the World Health Organization for the treatment of leprosy in combination with dapsone and rifampicin. It is an iminophenazine derivative and classified as a Biopharmaceutics Classification System (BCS) class II drug because of poor aqueous solubility (10 mg L–1). Despite it being a very classical drug known for more than five decades, there is no systematic study of CFZ salts for solubility and stability enhancement. We report a solid form screen of CFZ with pharmaceutically acceptable coformers/acids. Salts of CFZ with methanesulfonic acid, maleic acid, isonicotinic acid, nicotinic acid, malonic acid, and salicylic acid in an equimolar ratio as well as an amorphous phase of CFZ are reported. All new solid phases were characterized by FT-IR, powder X-ray diffraction, and differential scanning calorimetry, and confirmed by single crystal X-ray diffraction. The acid proton is transferred to the imine nitrogen of CFZ in a...

Clofazimine Mesylate: A High Solubility Stable Salt

Mycolic acids are major and specific long-chain fatty acids that represent essential components of the Mycobacterium tuberculosis cell envelope. They play a crucial role in the cell wall architecture and impermeability, hence the natural resistance of mycobacteria to most antibiotics, and represent key factors in mycobacterial virulence. Biosynthesis of mycolic acid precursors requires two types of fatty acid synthases (FASs), the eukaryotic-like multifunctional enzyme FAS I and the acyl carrier protein (ACP)-dependent FAS II systems, which consists of a series of discrete mono-functional proteins, each catalyzing one reaction in the pathway. Unlike FAS II synthases of other bacteria, the mycobacterial FAS II is incapable of de novo fatty acid synthesis from acetyl-coenzyme A, but instead elongates medium-chain-length fatty acids previously synthesized by FAS I, leading to meromycolic acids. In addition, mycolic acid subspecies with defined biological properties can be distinguished according to the chemical modifications decorating the meromycolate. Nearly all the genetic components involved in both elongation and functionalization of the meromycolic acid have been identified and are generally clustered in distinct transcriptional units. A large body of information has been generated on the enzymology of the mycolic acid biosynthetic pathway and on their genetic and biochemical/structural characterization as targets of several antitubercular drugs. This chapter is a comprehensive overview of mycolic acid structure, function, and biosynthesis. Special emphasis is given to recent work addressing the regulation of mycolic acid biosynthesis, adding new insights to our understanding of how pathogenic mycobacteria adapt their cell wall composition in response to environmental changes.

The Molecular Genetics of Mycolic Acid Biosynthesis.

Probing the Mechanism of the Mycobacterium tuberculosis β-Ketoacyl-Acyl Carrier Protein Synthase III mtFabH FACTORS INFLUENCING CATALYSIS AND SUBSTRATE SPECIFICITY

Molecular modeling and simulation of Mycobacterium tuberculosis cell wall permeability.

Construction, molecular modeling, and simulation of Mycobacterium tuberculosis cell walls.

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Molecular modeling and simulation of Mycobacterium tuberculosis cell wall permeability.

Construction, molecular modeling, and simulation of Mycobacterium tuberculosis cell walls.