Role of very-long-chain acyl-coenzyme A synthetase in X-linked adrenoleukodystrophy

X-linked adrenoleukodystrophy (X-ALD) is characterized biochemically by dec reased ability of cells to activate (via very-long-chain acyl-coenzyme A sy nthetase [VLCS]) and subsequently degrade very-long-chain fatty acids in pe roxisomes. It is noteworthy that the gene defective in X-ALD encodes ALDP, a peroxisomal membrane protein unrelated to VLCS. We cloned human VLCS (hVL CS) and found that peroxisomes from X-ALD fibroblasts contained immunoreact ive hVLCS, refuting the earlier hypothesis that ALDP is required to anchor VLCS to the peroxisomal membrane. Furthermore, hVLCS was topographically or iented facing the peroxisomal matrix in both control and X-ALD fibroblasts, contradicting the alternative hypothesis that ALDP is required to transloc ate VLCS into peroxisomes. However, overexpression of both hVLCS and ALDP i n X-ALD fibroblasts synergistically increased very-long-chain fatty acid P- oxidation, indicating that these proteins interact functionally.