INTRINSIC STEROL AND PHOSPHATIDYLCHOLINE TRANSFER ACTIVITIES OF 17-BETA-HYDROXYSTEROID DEHYDROGENASE TYPE-IV

Previous studies have shown that the 80 kDa 17 beta-hydroxysteroid deh ydrogenase (17 beta-HSD) type TV comprises distinct domains, including an N-terminal region related to the short chain alcohol dehydrogenase multigene family and a C-terminal part related to the lipid transfer protein sterol carrier protein 2 (SCP2). In this study, we have invest igated whether the SCP2-related part of the 80 kDa protein leads to an intrinsic sterol and phospholipid transfer activity, as shown earlier for the 60 kDa SCP2-related peroxisomal 3-ketoacyl CoA thiolase with intrinsic sterol and phospholipid transfer activity called sterol carr ier protein x (SCPx). Our results indicate that a fraction rich in the 80 kDa form of 17 beta-HSD type IV exhibits high transfer activities for 7-dehydrocholesterol and phosphatidylcholine. In addition, a purif ied recombinant peptide derived from the SCP2-related domain of the 17 beta-HSD type IV has about 30% of the transfer activities for 7-dehyd rocholesterol and phosphatidylcholine seen with purified recombinant h uman SCP2. We conclude that the 80 kDa type IV 17 beta-HSD represents a potentially multifunctional protein with intrinsic in vitro sterol a nd phospholipid transfer activity in addition to its enzymatic activit y.