Structure and function of steroid dehydrogenases involved in hypertension, fertility, and cancer

Area of Science:

• Biochemistry and Structural Biology
• Enzymology
• Molecular Biology

Background:

• Short-chain dehydrogenase reductase (SDR) enzymes play vital roles in mammalian reproduction, hypertension, neoplasia, and digestion.
• Understanding the three-dimensional structures of SDR enzymes is key to elucidating their catalytic mechanisms and inhibition strategies.

Purpose of the Study:

• To determine the three-dimensional structures of SDR enzymes and their complexes with inhibitors.
• To investigate the molecular mechanisms of enzyme inhibition and substrate binding.
• To identify conserved residues and structural features within the SDR family.

Main Methods:

• X-ray crystallography was employed to determine the structures of five SDR family members.
• Complex structures, such as 3 alpha,20 beta-hydroxysteroid dehydrogenase (3 alpha,20 beta-HSD) with carbenoxolone, were analyzed.
• Superposition of alpha-carbon backbones of cofactor binding domains provided insights into conserved residues.

Main Results:

• Structural analysis revealed the conserved catalytic triad, keto-hydroxyl interconversion mechanisms, and basis for selectivity.
• Carbenoxolone was identified as a potent inhibitor of bacterial 3 alpha,20 beta-HSD, acting via competitive substrate binding.
• Conserved residues, including the YXXXK sequence, are located in the core and cofactor binding domain, not the substrate pocket.

Conclusions:

• The study provides detailed structural insights into SDR enzyme function, substrate binding, and inhibition mechanisms.
• Structural data for 3 alpha,20 beta-HSD and 17 beta-hydroxysteroid dehydrogenase type 1 (17 beta-HSD) offer models for related enzymes.
• Understanding conserved structural elements aids in predicting the function and designing inhibitors for the broader SDR family.