| Δ3-Δ2-Enoyl-CoA isomerase from the yeast Saccharomyces cerevisiae: Molecular and structural characterization | ||
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Fatty acids are an important source of metabolic energy. When stored in adipose tissue as triacylglycerols, they are the most concentrated form of energy storage in animals. Fatty acids and their derivatives also have other physiological functions. They can act as components of biological membranes and serve as hormones and intracellular messengers.
For energy metabolism, fatty acids, activated into their coenzyme A esters, are degraded by sequential removal of acetyl-CoA units during a process called β -oxidation. Acetyl-CoA molecules are further targeted to the citric acid cycle for complete oxidation to CO2 and water or to ketone body formation in liver or cholesterolgenesis. In mammalian cells, β -oxidation occurs in two subcellular organelles, mitochondria and peroxisomes (Lazarow & De Duve 1976). In the yeast Saccharomyces cerevisiae (S. cerevisiae), however, fatty acids are degraded only in peroxisomes (Kunau et al. 1988). One cycle of β -oxidation of a saturated fatty acid consists of four subsequent enzymatic reactions: dehydrogenation/oxidation, hydration, second dehydrogenation and thiolytic cleavage. For the metabolism of double bonds in unsaturated fatty acids, auxiliary enzymes, such as Δ3-Δ2-enoyl-CoA isomerase, 2,4-dienoyl-CoA reductase and Δ3,5-Δ2,4-dienoyl-CoA isomerase, are needed.
Proteins can be classified into superfamilies according to their amino acid sequence similarity. Most enzymes participating in the hydration and isomerization reactions of β -oxidation belong to the low-similarity hydratase/isomerase superfamily of enzymes (Müller-Newen et al. 1995). In addition to β -oxidation, members of this superfamily also participate in many other metabolic pathways. Hydratase/isomerase superfamily members are thought to have evolved from a common ancestor and, despite the large variability of reactions they are able to catalyze, they appear to be both structurally and mechanistically related.
In this study, the gene encoding the S. cerevisiae Δ3-Δ2-enoyl-CoA isomerase, a member of the hydratase/isomerase superfamily, was identified, the gene product was purified, characterized and crystallized, and its three-dimensional structure with and without an active site ligand was determined.