Rational proteomics IV: modeling the primary function of the mammalian 17β-hydroxysteroid dehydrogenase type 8

Significant sequence homology has been detected between prokaryotic β-ketoacyl-[acyl carrier protein] reductases (BKR) and eukaryotic 17β-hydroxysteroid dehydrogenases type 8 (17β-HSD_8). Three-dimensional models of ternary complexes of human 17β-HSD_8 with NAD cofactor and two chemically distinct substrates, the BKR substrate {CH3-(CH2)12-CO-CH2-CO-S-[ACP]} and the HSD substrate {estradiol} have been constructed (the atomic coordinates are available on request; e-mail: pletnev@hwi.buffalo.edu). The more extensive and specific interactions of 17β-HSD_8 with the BKR substrate compared to interactions with estradiol raise a serious question about the enzyme's primary function in vivo and suggest that it is likely to be involved in the regulation of fatty acid metabolism rather than in the steroid-dependent activity that has been demonstrated in vitro.