StAR-like Activity and Molten Globule Behavior of StARD6, A Male Germ-Line Protein

详细信息    查看全文

• 作者：Himangshu S. Bose ; Randy M. Whittal ; Yong Ran ; Mahuya Bose ; Bo Y. Baker ; Walter L. Miller
• 刊名：Biochemistry
• 出版年：2008
• 出版时间：February 26, 2008
• 年：2008
• 卷：47
• 期：8
• 页码：2277 - 2288
• 全文大小：445K
• 年卷期：v.47,no.8(February 26, 2008)
• ISSN：1520-4995

文摘

The steroidogenic acute regulatory protein (StAR) belongs to a family of 15 StAR-relatedlipid transfer (START) domain proteins termed StARD1-StARD15. StAR (StARD1) induces adrenaland gonadal steroidogenesis by moving cholesterol from the outer mitochondrial membrane to the innermitochondrial membrane by an unclear process that involves conformational changes that have beencharacterized as a molten globule transition. We expressed, purified, and assessed the activity andcholesterol-binding behavior of StARD1 and StARD3-D7, showing that StARD6 had activity equal toStARD1, whereas StARD4, D5, and D7 had little or no activity with adrenal mitochondria in vitro. Partialproteolysis examined by mass spectrometry suggests that StARD6 has a protease-sensitive C-terminus,similar to but smaller than that of StARD1. Experiments using urea denaturation, stopped-flow kineticsand measurements of mitochondrial membrane association suggests that StARD1 and StARD6 both unfoldand refold slowly with similar kinetic patterns. Isothermal titration calorimetry suggests that StARD6interacts with mitochondrial membranes as well as or better than StARD1. Computational modeling ofStARD6 suggests that it has a similar fold to StARD1, with a hydrophobic sterol-binding pocket and aunique C-terminal extension. StARD6, which is expressed only in male germ-line cells, thus exhibitsbiological and biophysical properties that imply a role in steroidogenesis.