Mechanism of action of steroidogenic acute regulatory protein (StAR)

描述(申请人提供)：类固醇合成的限速步骤是胆固醇从线粒体膜外膜(OMM)到线粒体膜内膜(IMM)的运动。类固醇合成急性调节蛋白(STAR)通过一种未知的机制促进胆固醇从OMM向IMM的移动，从而调节底物流向P450scc以促进类固醇的生成。STAR属于一个被称为STAR(STAR相关脂质转运域)的蛋白质家族，其中STAR是主要成员。STAR突变会导致一种名为先天性肾上腺增生症的潜在致命疾病，在这种疾病中，所有类固醇激素的合成都会受损，胎儿在出生后不久就会死亡。恒星活动与其在OMM的驻留时间成正比。我们的初步结果表明：1)STAR的导入机制是独特的，2)STAR的暂停序列在STAR的折叠和活性中具有明显的作用，3)STAR在一小时内运输超过100个分子的胆固醇，IV)STAR是通过几种蛋白质的复合体导入的，以及v)STAR是分两步导入的。为了了解STAR加工和输入线粒体的机制，我们提出了三个特定的目标。目的1是确定新合成的STAR的活性机制。这对于理解STAR如何在如此短的半衰期内发挥作用，以及它如何在没有N端序列的情况下到达OMM是至关重要的。在目标2中，我们建议确定STAR作用的线粒体位置，以了解OMM驻留蛋白VDAC 1和2(电压依赖阴离子通道)对STAR的易位机制。在目标3中，我们建议通过OMM相关的脂膜来确定STAR的去折叠机制，并揭示为什么特定的起始结构域比另一个更活跃。实现这些目标将帮助我们扩大我们对STAR与OMM相互作用机制的了解，以及II)扩大我们对OMM在帮助STAR展开从而动员胆固醇运输中的作用的理解。完成这些目标将有助于我们理解细胞脂代谢的广泛方面，以及一系列广泛的出生缺陷、胚胎发育障碍和遗传性疾病。

DESCRIPTION (provided by applicant): The rate-limiting step in steroidogenesis is the movement of cholesterol from the outer mitochondrial membrane (OMM) to inner mitochondrial membrane (IMM). The steroidogenic acute regulatory protein (StAR) by an unknown mechanism facilitates the movement of cholesterol from the OMM to IMM, thus regulating the flow of substrate to P450scc for steroidogenesis. StAR belongs to a family of proteins called START (StAR related lipid transport domain), where StAR is the primary member. StAR mutations cause a potentially lethal disease called congenital adrenal hyperplasia, in which the synthesis of all steroid hormones is impaired, and the fetuses die shortly after birth. StAR activity is directly proportional to its residency time at the OMM. Our preliminary results show that i) the import mechanism of StAR is unique, ii) the StAR pause sequence has a distinct role in StAR folding and activity, iii) StAR transports more than 100 molecules of cholesterol in one hour, iv) StAR is imported through a complex of several proteins, and v) StAR is imported in a two step process. To understand the mechanism of StAR processing and import into mitochondria, we propose three specific aims. Aim 1 is to determine the mechanism of activity of newly synthesized StAR. This is critical in understanding how StAR functions with such a short half- life, and how it can reach the OMM with out the N-terminal sequence. In aim 2, we proposed to determine the mitochondrial site of StAR action, in order to understand the translocation mechanism of StAR by OMM resident proteins VDAC 1 and 2 (Voltage Dependent Anion Channel). In aim 3, we proposed to determine the unfolding mechanism of StAR by the OMM associated lipid membrane, and to uncover why a specific START-domain is more active than the other. Fulfilling these aims will, I) help us to expand our knowledge about the mechanism of interaction of StAR with the OMM and II) expand our understanding about the role of OMM that help in StAR unfolding and thus mobilization of cholesterol transport. Completing these aims will help us in the understanding of broad aspects of cellular lipid metabolism and also to a broad array of birth defects, disorders of embryogenesis and genetic diseases.