Fig. 2

GC-FID chromatograms of secreted lipids from K27(DE3) E. coli strains expressing wild-type or mutant ALTs. β-keto fatty acids produced by ALTs were decarboxylated to methylketones with heat and acid treatment prior to identification and quantification by GC-FID and GC-MS analysis. Compounds corresponding to peaks are labelled above the chromatograms (FA = fully reduced fatty acids, MK = methylketone, 3-OH FA = 3-hydroxy fatty acid). In the MtALT2-A mutant, aa31–36 have been replaced with 31-CQHCGD-36 from MtALT1, while the rest of the MtALT2 protein backbone was left unaltered. The AtALT3-A mutant contains a single R35M substitution, such that aa31–36 reads 31-CQHGMH-36, like AtALT4. In the ZmALT1-A mutant, 31-CQHGRH-36 have been replaced with 31-IEIARQ-36 from ZmALT3, with the rest of the ZmALT1 backbone remaining intact