SUMMARY PARAGRAPH for ETR1
ETR1 encodes a member of the medium chain dehydrogenase/reductase family with 2-enoyl thioester reductase activity (E.C. number 1.3.1.-) (1). Etr1p is located in mitochondria, where it has a probable role in fatty acid synthesis (1). The etr1 null mutant is unable to grow on nonfermentable carbon sources and displays decreased mitochondrial cytochrome content. The null phenotypes are complemented by expression of the Etr1p ortholog from Candida tropicalis, or by targeting E. coli FabI, a NADPH-dependent 2-enoyl-acyl carrier protein reductase, to mitochondria (1). Although a previous study suggested that Etr1p (formerly known as Mrf1'p) is localized to the nucleus (2), a more recent study confirmed its mitochondrial localization and also showed that, when artificially targeted to the nucleus, Etr1p fails to complement the respiratory growth deficiency caused by the etr1 null mutation (1).
About the medium-chain dehydrogenase/reductase (MDR) family
Medium-chain dehydrogenase/reductases (MDRs), sometimes referred to as long-chain dehydrogenases (3), constitute an ancient and widespread enzyme superfamily with members found in Bacteria, Archaea, and Eukaryota (4, 5). Many MDR members are basic metabolic enzymes acting on alcohols or aldehydes, and thus these enzymes may have roles in detoxifying alcohols and related compounds, protecting against environmental stresses such as osmotic shock, reduced or elevated temperatures, or oxidative stress (4). The family also includes the mammalian zeta-crystallin lens protein, which may protect the lens against oxidative damage and enzymes which produce lignocellulose in plants (4).
MDR enzymes typically have subunits of about 350 aa residues and are two-domain proteins, with a catalytic domain and a second domain for binding to the nicotinamide cofactor, either NAD(H) or NADP(H) (4, 5). They contain 0, 1, or 2 zinc atoms (6). When zinc is present, it is involved in catalysis at the active site.
Based on phylogenetic and sequence analysis, the members of the MDR superfamily can be further divided into more closely related subgroups (4, 5). In families which are widespread from prokaryotes to eukaryotes, some members appear conserved across all species, while others appear to be due to lineage specific duplications. Some subgroups are only found in certain taxa. S. cerevisiae contains fifteen (4) or twenty-one (5) members of the MDR superfamily, listed below. The difference in number is due to six sequences that were included as members of the quinone oxidoreductase family by Riveros-Rosas et al. (5) but not by Nordling et al. (4).
Zinc-containing enzyme groups:
- PDH; "polyol" dehydrogenase family - BDH1, BDH2, SOR1, SOR2, XYL2
- ADH; class III alcohol dehydrogenase family - SFA1
- Y-ADH; "yeast" alcohol dehydrogenase family - ADH1, ADH2, ADH3, ADH5
- CADH; cinnamyl alcohol dehydrogenase family - ADH6, ADH7
Non-zinc-containing enzyme groups:
- NRBP; nuclear receptor binding protein (5) or MRF; mitochondrial respiratory function (4) family - ETR1
- QOR; quinone oxidoreductase family - ZTA1 (4, 5), AST1, AST2, YCR102C, YLR460C, YMR152W, YNL134C (5)
- LTD; leukotriene B4 dehydrogenases - YML131W
- ER; enoyl reductases (5) or ACR; acyl-CoA reductase (4) family - no members in S. cerevisiae
Last updated: 2002-12-04 
