Domains of the tetrafunctional protein acting in glyoxysomal fatty acid beta-oxidation. Demonstration of epimerase and isomerase activities on a peptide lacking hydratase activity.

Peroxisomes from different eukaryotic organisms house a multifunctional protein acting in fatty acid beta-oxidation. In plant glyoxysomes, one of the isoforms of this protein contains the activities of L-3-hydroxyacyl-CoA hydrolyase (EC 4.2.1.17), L-3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.211), D-3-hydroxyacyl-CoA epimerase, and delta 3,delta 2-enoyl-CoA isomerase (EC 5.3.3.8). This was demonstrated after molecular cloning of a cDNA coding for a protein of 79047 Da and its bacterial expression. Chromatographic purification yielded a monomeric protein exhibiting all four activities. In addition, mutant forms were prepared, and peptides representing single domains were purified. Peptides containing the N-terminal region showed D-3-hydroxyacyl-CoA epimerase and delta 3,delta 2-enoyl-CoA isomerase activities but lacked 2-trans-enoyl-CoA hydratase and L-3-hydroxyacyl-CoA dehydrogenase activities. Using the N-terminal fragment, we demonstrated that the D-3-hydroxyacyl-CoA converting activity is actually an epimerase rather than part of a combined water eliminating and water attaching system. The C-terminal half of the multifunctional protein represents the dehydrogenase domain.