Octanoylation of the lipoyl domains of the pyruvate dehydrogenase complex in a lipoyl‐deficient strain of Escherichia coli

Summary The overexpression of a subgene encoding a hybrid lipoyl domain of the dihydrolipoamide acetyltransferase component of the pyruvate dehydrogenase complex of Escherichia coli has previously bee shown to result in the formation of lipoylated an unlipoylated products. Overexpression of the same subgene in a lipoic acid biosynthesis mutant growing under lipoate‐deficient conditions has now bee shown to produce domains modified by octanoylation as well as unmodified domains. It was concluded from the mass of a lipoyl‐binding‐site peptide that the modification involves N6‐octanoylation of the lysin residue (Lys244) that is normally lipoylated, and this was confirmed by the trypsin‐insensitivity of the corresponding Lys244‐Ala245 bond, and the absence c modification in a mutant domain in which Lys244 is replaced by Gin. This novel protein modification raise interesting questions concerning the pathway of lipoic acid biosynthesis and the mechanism of enzyme lipoylation.