Expansion of the mammalian 3β‐hydroxysteroid dehydrogenase/plant dihydroflavonol reductase superfamily to include a bacterial cholesterol dehydrogenase, a bacterial UDP‐galactose‐4‐epimerase, and open reading frames in vaccinia virus and fish lymphocystis disease virus

摘要

>Mammalian 3β-hydroxysteroid dehydrogenase and plant dihydroflavonol reductases are descended from a common ancestor. Here we present evidence that Nocardia cholesterol dehydrogenase, E. coli UDP-galactose-4 epimerase, and open reading frames in vaccinia virus and fish lymphocystis disease virus are homologous to 3β-hydroxysteroid dehydrogenase and dehydroflavonol reductase. Analysis of a multiple alignment of these sequences indicates that viral ORFs are most closely related to the mammalian 3β-hydroxysteroid dehydrogenases. The ancestral protein of this superfamily is likely to be one that metabolized sugar nucleotides. The sequence similarity between 3β-hydroxysteroid dehydrogenase and the viral ORFs is sufficient to suggest that these ORFs have an activity that is similar to 3β-hydroxysteroid dehydrogenase or cholesterol dehydrogenase, although the putative substrates are not yet known.