Human very-long-chain acyl-CoA synthetase: Cloning, topography, and relevance to branched-chain fatty acid metabolism

Very-long-chain acyl-CoA synthetases (VLCS) activate very-long-chain fatty acids (VLCFA) containing 22 or more carbons to their CoA derivatives. We cl oned the human ortholog (hVLCS) of the gene encoding the rat liver enzyme ( rVLCS). Both hVLCS and rVLCS contain 620 amino acids, are expressed primari ly in liver and kidney, and have a potential peroxisome targeting signal 1 (-LKL) at their carboxy termini. When expressed in COS-1 cells, hVLCS activ ated the VLCFA lignoceric acid (C24:0), a long-chain fatty acid (C16:0), an d two branched-chain fatty acids, phytanic acid and pristanic acid. Immunof luorescence and immunoblot studies localized hVLCS to both peroxisomes and endoplasmic reticulum. In peroxisomes of HepG2 cells, hVLCS was topographic ally oriented facing the matrix and not the cytoplasm. This orientation, co upled with the observation that hVLCS activates branded-chain fatty acids, suggests that hVLCS could play a role in the intraperoxisomal reactivation of pristanic acid produced via a-oxidation of phytanic acid. (C) 1999 Acade mic.