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Journal of Lipid Research, Vol. 43, 2031-2036, December 2002
Copyright © 2002 by Lipid Research, Inc.

Review

A second gene for peroxisomal HMG-CoA reductase? A genomic reassessment

Rainer Breitling and Skaidrite K. Krisans¹

Department of Biology, San Diego State University, San Diego, CA

¹ To whom correspondence should be addressed. e-mail: skrisans{at}sunstroke.sdsu.edu

HMG-CoA reductase (HMGCR) catalyzes the conversion of HMG-CoA to mevalonate, the rate-limiting step of eukaryotic isoprenoid biosynthesis, and is the main target of cholesterol-lowering drugs. The classical form of the enzyme is a transmembrane-protein anchored to the endoplasmic reticulum. However, during the last years several lines of evidence pointed to the existence of a second isoform of HMGCR localized in peroxisomes, where mevalonate is converted further to farnesyl diphosphate. This finding is relevant for our understanding of the complex regulation and compartmentalization of the cholesterogenic pathway. Here we review experimental evidence suggesting that the peroxisomal activity might be due to a second HMGCR gene in mammals. We then present a comprehensive analysis of completely sequenced eukaryotic genomes, as well as the human and mouse genome drafts. Our results provide evidence for a large number of independent duplications of HMGCR in all eukaryotic kingdoms, but not for a second gene in mammals.

We conclude that the peroxisomal HMGCR activity in mammals is due to alternative targeting of the ER enzyme to peroxisomes by an as yet uncharacterized mechanism.

Abbreviations: CHO, Chinese hamster ovary; ER, endoplasmic reticulum; HMGCR, HMG-CoA reductase

Supplementary key words genome duplication • HMG-CoA reductase isozymes • alternative subcellular localization • cholesterol metabolism

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