Biosynthetic Pathways of Mycobacterial Cell Envelope Components

The mycobacterial cell envelope is a multilayered structure essential to viability, virulence and drug resistance. At its core lies the peptidoglycan layer, a mesh of N-acetylglucosamine–N-acetylmuramic acid repeats cross-linked by peptides. Attached to this is arabinogalactan, a heteropolysaccharide that secures long-chain mycolic acids, forming the characteristic mycomembrane. Biosynthesis of these layers relies on lipid carriers such as decaprenyl phosphate, which shuttles sugar moieties to polymer-forming enzymes. Galactan chains are elongated by galactofuranosyltransferases, whereas arabinan assembly is mediated by a suite of arabinofuranosyltransferases. Concurrently, fatty acid synthase systems and polyketide synthase Pks13 generate mycolic acids, which are ligated to arabinogalactan by antigen 85 complex mycolyl transferases. In parallel, phosphatidyl-myo-inositol mannosides (PIMs) and higher lipoglycans—including lipomannan and lipoarabinomannan—arise from sequential mannosylation by PimA and PimB′, culminating in complex glycolipids that modulate host–pathogen interactions. The precision of these pathways presents multiple enzymatic targets for antibiotic development and underpins efforts to overcome drug resistance.

Research from Nature Portfolio

Recent cryogenic electron microscopy studies of a membrane-bound phosphoribosyltransferase have elucidated its trimeric UbiA-like fold and inverting mechanism for transferring phosphoribose to decaprenyl phosphate, providing atomic-level insight into early cell wall precursor formation. Complementary work has identified distinct families of glycoside hydrolases capable of degrading the d-arabinan core of arabinogalactan. Conserved endo- and exo-acting enzymes, belonging to DUF2961 and DUF4185 families, show differential substrate preferences for arabinogalactan and lipoarabinomannan, suggesting intrinsic roles in cell envelope remodelling and potential avenues for therapeutic intervention.

Biosynthetic Pathways of Mycobacterial Cell Envelope Components publication trend

The graph below shows the total number of articles in biosynthetic pathways of mycobacterial cell envelope components across all publications each year (not limited to Nature Index journals).

Technical terms

Peptidoglycan: A polymer of sugar chains cross-linked by peptides that provides mechanical strength to the cell wall.

Arabinogalactan: A heteropolysaccharide linking peptidoglycan to mycolic acids, forming the mAGP complex.

Mycolic acids: Very long-chain fatty acids that constitute the hydrophobic core of the mycomembrane.

Decaprenyl phosphate: A long-chain lipid carrier that transfers sugar precursors across the cytoplasmic membrane.

Phosphoribosyltransferase: An enzyme that catalyses the transfer of phosphoribose units from a nucleotide donor to an acceptor lipid.

Glycoside hydrolase: An enzyme that cleaves glycosidic bonds within polysaccharides, enabling polymer turnover.

Mannosyltransferase: An enzyme that transfers mannose residues from a nucleotide sugar donor onto lipid or sugar acceptors.

Lipoglycan: A lipid-linked polysaccharide such as lipomannan or lipoarabinomannan that participates in host immune modulation.

References

1. Structural analysis of phosphoribosyltransferase-mediated cell wall precursor synthesis in Mycobacterium tuberculosis. Nature Microbiology (2024).
2. Identification of d-arabinan-degrading enzymes in mycobacteria. Nature Communications (2023).
3. Cell-autonomous targeting of arabinogalactan by host immune factors inhibits mycobacterial growth. eLife (2024).
4. Definition of the First Mannosylation Step in Phosphatidylinositol Mannoside Synthesis PimA IS ESSENTIAL FOR GROWTH OF MYCOBACTERIA*. Journal of Biological Chemistry (2002).
5. New Insights into the Early Steps of Phosphatidylinositol Mannoside Biosynthesis in Mycobacteria PimB′ IS AN ESSENTIAL ENZYME OF MYCOBACTERIUM SMEGMATIS*. Journal of Biological Chemistry (2009).