Mitochondrial and peroxisomal targeting of 2-methylacyl-CoA racemase in humans

Abstract

2-Methylacyl-CoA racemase is an auxiliary enzyme required for the peroxisomal β-oxidative breakdown of (2R)-pristanic acid and the (25R)-isomer of C27 bile acid intermediates. The enzyme activity is found not only in peroxisomes but also is present in mitochondria of human liver and fibroblasts. The C terminus of the human racemase, a protein of 382 amino acids with a molecular mass of 43,304 daltons as deduced from its cloned cDNA, consists of KASL. Hitherto this sequence has not been recognized as a peroxisomal targeting signal (PTS1). From the in vitro interaction between recombinant racemase and recombinant human PTS1 receptor (Pex5p), and the peroxisomal localization of green fluorescent protein (GFP) fused to the N terminus of full-length racemase or its last six amino acids in tranfected Chinese hamster ovary (CHO) cells, we concluded that ASL is a new PTS1 variant. To be recognized by Pex5p, however, the preceding lysine residue is critical. As shown in another series of transfection experiments with GFP fused to the C terminus of the full-length racemase or racemase with deletions of the N terminus, mitochondrial targeting information is localized between amino acids 22 and 85. Hence, our data show that a single transcript gives rise to a racemase protein containing two topogenic signals, explaining the dual cellular localization of the activity.—Amery, L., M. Fransen, K. De Nys, G. P. Mannaerts, and P. P. Van Veldhoven. Mitochondrial and peroxisomal targeting of 2-methylacyl-CoA racemase in humans. J. Lipid Res. 2000. 41: 1752–1759.

Keywords

• cholestanoic acid
• pristanic acid
• β-oxidation
• peroxins
• bile acids
• epimerase