Fig. 3: Genomic loci of mutations within mycolic acid biosynthetic pathway.
a Mutations in GAM6, GAM7, GAM10, GAM11 and GAM12 are shown in the first locus by a red triangle and SNPs indicated above. GAM12 contains a missense mutation in the predicted aftB gene. The remaining mutations all occur in different locations in pks13. Genes shaded in grey are predicted to encode proteins involved in AG and MA biosynthesis pathways. b Schematic of Pks13 protein, orange segments indicate the catalytic N-terminal acyl carrier proteins (ACP), ketoacyl synthase (KS), acyl transferase (AT), C-terminal ACP and thioesterase (TE) domains49. Red triangles indicate the location of the mutations in GAM6, GAM7, GAM10 and GAM11. Blue oval represents PptT protein priming the Pks13 N-terminal and C-terminal ACP domains with 4’-phosphopantetheinyl (P-pant) arm49. Mutations acquired in GAM1, GAM4 and GAM9 within PptT likely result in protein dysfunction (indicated by the red Xs). c Amino acid alignments comparing the conserved KS and TE catalytic domains of each GAM with the G. amarae CON44T (Accession number: CP045810), and M. tuberculosis H37Rv (Accession number: NC_000962.3)49. Catalytic residues identified in M. tuberculosis49, are highlighted in blue, with red triangles indicating the positions of amino acid substitutions/deletions. Residue discrepancies are highlighted in grey. In GAM10 the predicted catalytic cysteine (Cys-303) is substituted with tryptophan (Try-303). In the GAM7 TE domain, a cysteine substitution of glycine (Gly-1606) occurred two residues downstream of the predicted catalytic serine (Ser-1606, Ser-1533 in M. tuberculosis). Further downstream within the TE domain GAM11 and GAM6 encode a Ser-1755 substitution and Val-1765-Gln-Ile-Gly-1768 deletions respectively. d GAM1, GAM4 and GAM9 share mutations within the pptT gene, with red triangles indicating the corresponding mutations above. e Basic overall mycolic acid biosynthetic pathway. Multiple proteins are involved in the coordination of the final condensation of MA, a complex process that requires several precursor reactions20,49. Pks13 condensase requires PptT posttranslational priming and works in concert with various acyl carrier proteins to catalyse the biosynthesis of MA, by condensing the FAS I and FAS II cycle outputs20,50. In combination with peptidoglycan, trehalose and arabinogalactan (outputs in green boxes), MA forms the mycomembrane. Red text highlight gene mutations identified in each GAM. Created in BioRender. Rose, J. (2025) http://BioRender.com/o17z397.
