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Biochemistry and molecular biology
The maintenance of cellular levels of free fatty acids and acyl-CoAs, the activated form of free fatty acids, is extremely important as imbalances in lipid metabolism have serious consequences for human health. Acyl-CoA thioesterases (ACOTs) hydrolyze acyl-CoAs to the free fatty acid and CoASH, and thereby have the potential to regulate intracellular levels of these compounds. We have previously identified and characterized a mouse ACOT gene cluster, comprised of six genes that apparently arose by gene duplications, encoding acyl- CoA thioesterases with localizations in cytosol (ACOT1), mitochondria (ACOT2) and peroxisomes (ACOT3-6). However, the corresponding human gene cluster contains only three genes, ACOT1, ACOT2 and ACOT4 coding for full-length thioesterase proteins, of which only one is peroxisomal (ACOT4). We therefore set out to characterize the human genes, and we here show that the human ACOT4 protein catalyzes the activities of three mouse peroxisomal ACOTs (ACOT3, 4, and 5), being active on succinyl-CoA and mediumto long-chain acyl-CoAs, while ACOT1 and ACOT2 carry out similar functions to the corresponding mouse genes. These data strongly suggest that the human ACOT4 gene has acquired the functions of three mouse genes by a functional convergent evolution that also provides an explanation for the unexpectedly low number of human genes.
Hunt, M. C., Rautanen, A., Westin, M. A. K., Svensson, L. T., Alexson, S. E. H. Analysis of mouse and human acyl-CoA thioesterase (ACOT) gene clusters shows that convergent functional evolution results in a reduced number of peroxisomal ACOTs. FASEB J. (2006) 20 (11) 1855-1864. doi:10.1096/fj.06-6042com