Human placental 17 beta-hydroxysteroid dehydrogenase is homologous to NodG protein of Rhizobium meliloti

The amino acid sequence of human placental 17 beta-hydroxysteroid dehydrogenase (17 beta-OH-steroid dehydrogenase) was found to be similar to that of the NodG protein of Rhizobium meliloti. The computer-based comparison score is 11.5 SD higher than that obtained with 2500 comparisons of randomized sequences of these proteins. The probability of getting such a score by chance is 6 x 10(-31). 17 beta-OH-steroid dehydrogenase is also similar to Klebsiella aerogenes ribitol dehydrogenase and Escherichia coli glucitol-6-phosphate dehydrogenase. We propose that the steroid recognition site on 17 beta-OH-steroid dehydrogenase evolved from an ancestral recognition site for polyols such as ribitol and glucitol-6-phosphate.