5-methyl-3-oxohexanoyl-[acp];
[lipoyl-carrier protein]-N6-[(R)-dihydrolipoyl]-L-lysine [CPD:C16832];
CO2 [CPD:C00011];
-a [lipoyl-carrier protein]-N6-[(3-methyl-2-oxobutanoyl)-(R)-lipoyl]-L-lysine
Comment
The enzyme, characterized from an environmental DNA sample and expressed in Paraburkholderia graminis, is a complex enzyme whose purpose is to divert branched-chain 2-oxo acids to production of branched-chain N-acyl amino acids by producing branched 3-oxoacyl-[acp] molecules. NasB accepts branched-chain 2-oxoacids such as 4-methyl-2-oxopentanoate, and catalyses a decarboxylative transfer to a thiamine diphosphate cofactor, followed by a transfer to a lipoyl cofactor, and finally a second decarboxylative transfer to the malonyl-[acp] acceptor. The products, such as 5-methyl-3-oxohexanoyl-[acp], can be extended by the fatty acid synthase system to form branched long-chain fatty-acyl-[acp] molecules, which serve as substrates for EC 2.3.1.327, long-chain acyl-[acp]:L-phenylalanine N-acyltransferase (NasA). During the reaction the lipoyl cofactor is reduced to dihydrolipoyl, which must be oxidized back to lipoyl by an unknown enzyme.
