Lipid-Mediated Unfolding of 3尾-Hydroxysteroid Dehydrogenase 2 Is Essential for Steroidogenic Activity

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• 作者：Maheshinie Rajapaksha ; James L. Thomas ; Michael Streeter ; Manoj Prasad ; Randy M. Whittal ; John D. Bell ; Himangshu S. Bose
• 刊名：Biochemistry
• 出版年：2011
• 出版时间：December 27, 2011
• 年：2011
• 卷：50
• 期：51
• 页码：11015-11024
• 全文大小：520K
• 年卷期：v.50,no.51(December 27, 2011)
• ISSN：1520-4995

文摘

For inner mitochondrial membrane (IMM) proteins that do not undergo N-terminal cleavage, the activity may occur in the absence of a receptor present in the mitochondrial membrane. One such protein is human 3尾-hydroxysteroid dehydrogenase 2 (3尾HSD2), the IMM resident protein responsible for catalyzing two key steps in steroid metabolism: the conversion of pregnenolone to progesterone and dehydroepiandrosterone to androstenedione. Conversion requires that 3尾HSD2 serve as both a dehydrogenase and an isomerase. The dual functionality of 3尾HSD2 results from a conformational change, but the trigger for this change remains unknown. Using fluorescence resonance energy transfer, we found that 3尾HSD2 interacted strongly with a mixture of dipalmitoylphosphatidylglycerol (DPPG) and dipalmitoylphosphatidylcholine (DPPC). 3尾HSD2 became less stable when incubated with the individual lipids, as indicated by the decrease in thermal denaturation (T_m) from 42 to 37 掳C. DPPG, alone or in combination with DPPC, led to a decrease in 伪-helical content without an effect on the 尾-sheet conformation. With the exception of the 20 N-terminal amino acids, mixed vesicles protected 3尾HSD2 from trypsin digestion. However, protein incubated with DPPC was only partially protected. The lipid-mediated unfolding completely supports the model in which a cavity forms between the 伪-helix and 尾-sheet. As 3尾HSD2 lacks a receptor, opening the conformation may activate the protein.