octanoyltransferase

Octanoyltransferase is an enzyme that catalyzes the transfer of an octanoyl group from octanoyl-acyl carrier protein (octanoyl-ACP) to a lysine residue on a lipoyl domain of certain dehydrogenase complexes, forming an octanoyl-lipoyl precursor. In bacteria, the enzyme LipB carries out this transfer as part of the lipoic acid biosynthesis pathway. A subsequent enzyme, LipA, then introduces sulfur atoms to convert the octanoyl chain into the mature lipoyl prosthetic group attached to the protein.

The transfer mechanism typically involves formation of a thioester-linked octanoyl-enzyme intermediate via a catalytic cysteine residue in LipB, followed by transfer of the octanoyl group from the enzyme to the target lysine on the apo-lipoyl domain. This yields an octanoylated protein, which LipA subsequently converts into the functional lipoyl moiety required for enzyme catalysis in multi-subunit complexes.

Distribution and significance vary by organism, but octanoyltransferase enzymes are widespread in bacteria and are found in plastids of plants and algae. They are essential for the activity of several key multienzyme complexes, including pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and branched-chain α-keto acid dehydrogenase complexes. Defects in the lipoylation pathway can impair central metabolism and cellular energy production.

In the broader context, octanoyltransferase refers to LipB and related enzymes that initiate protein lipoylation by octanoyl transfer; some organisms use alternative routes that directly install the mature lipoyl group via lipoate-protein ligases. See also lipoic acid, lipoylation, LipB, LipA, LplA, and LIPT proteins.