TABLE 1.
Biosynthetic origin of each cyclopropane ring or methyl branch found in the M. tuberculosis mycolates pictured in Fig. 1a
| Lipid structure | Methyltransferase(s) | Reference(s) |
|---|---|---|
| Cyclopropane ring | ||
| α proximal (cis) | PcaA | 15 |
| α distal (cis) | MmaA2 (CmaA2) | 13; this study |
| Methoxy cis | MmaA2, CmaA2 | This study |
| Methoxy trans | CmaA2 | 14 |
| Keto cis | MmaA2, CmaA2 (?b) | This study |
| Keto trans | CmaA2 | 14 |
| Methyl groups | ||
| Methoxy group | MmaA3 | 4, 11 |
| Oxygenated mycolates; distal methyl branch | MmaA4 | 9-10, 26 |
| trans-cyclopropanated oxygenated mycolates, proximal methyl branch | MmaA1 | 27; this study |
| Unknown function | ||
| None | CmaA1 | 13; this study |
a
The first column lists each cyclopropane ring or methyl branch (see Fig. 1 for structures). The second column lists the enzymes that synthesize each modification. Two enzymes are listed without parentheses when the modification is lost only in a double mutant of the genes encoding the listed enzymes and not in either of the single mutants. When two enzymes are listed with one in parentheses, the parenthetical enzyme plays a secondary role that is evident only when the gene encoding the primary enzyme is deleted.
b
A third, as-yet-unidentified enzyme is also capable of this modification.