THE LINKING OF BETA‐OXIDATION TO CARDIOLIPIN REMODELING

Abstract

We previously identified a human linoleoyl‐Coenzyme A monolysocardiolipin (MLCL) acyltransferase activity (MLCL AT‐1) (Taylor and Hatch 2009 J. Biol. Chem. 284: 30360‐30371). This 59 kDa human protein was identical to the 74 kDa human α‐subunit of trifunctional protein (αTFP) minus the first 237 amino acids. Here we characterize the MLCL AT activity of αTFP. The 74 kDa αTFP exhibited MLCL AT activity and western blot analysis under non‐denaturing conditions revealed the presence of a 150 kDa protein indicative of the dimeric form of αTFP. NAD stimulated the MLCL AT activity of αTFP. Recombinant human αTFP exhibited specificity for linoleoyl‐CoA in the acylation of MLCL to cardiolipin (CL). Expression of αTFP increased MLCL AT activity and [1‐14C]linoleate incorporation into CL in Hela cells, whereas, RNAi knock down had the opposite effect. RNAi knock down of the β‐subunit of trifunctional protein increased MLCL AT activity indicating that αTFP has MLCL AT activity and the β‐subunit is a negative regulator of activity. Thyroxine‐treatment of rats, which increases MLCL AT activity, increased αTFP mRNA expression compared to euthyroid controls, whereas, propylthiouracil‐treatment, which reduced MLCL AT activity, had the opposite effect. The results clearly indicate that the 74 kDa human αTFP has MLCL AT activity and thus linking an enzyme of CL remodeling with β‐oxidation.