Octanoyl-[acyl-carrier-protein]-protein N-octanoyltransferase [1] (gene lipB) is the bacterial enzyme that transfers the octanoyl moiety of octanoyl-acyl carrier protein (octanoyl-ACP) to the lipoyl domains of the 2-oxoacid deshydrogenases and the H subunit of glycine cleavage enzyme.

via a thioester-linked octanoyl-LipBintermediate [zhao].

The Escherichia coli LipB reaction proceeds through an acyl-enzyme intermediate in which octanoate is first transferred from the thiol of ACP to a specific LipB thiol. The acyl-enzyme thioester bond is then attacked by the -amino group of the lipoyl domain lysine residue, resulting in the amide-linked octanoylated domains that are the substrates for sulfur insertion.

LipB shows no obvious sequence relatedness to proteins other than its homologues which are widely distributed among prokaryotic and eukaryotic organisms.

Such an enzyme has also be found in fungi [2], where it is located in the mitochondria. It also seems to exist in plants and is encoded in the chloroplast genome of the red alga Cyanidium caldarium.

As a signature for lipB, we selected the most conserved region, located in the central part of the enzyme. This region contains one of two conserved histidines.