SAT-347 Unfolding Generates an Active CYP11A1 for Mitochondrial Integration and Activity

Mitochondrial protein import and sorting are mediated by translocases. Precursor proteins with amino-terminal presequences transition from the translocase of the outer membrane (TOM) complex to the translocase of the inner membrane (TIM) complex. In adrenal and gonadal cells, the molecular mechanism of mitochondrial complex formation and electron transport to initiate and maintain steroid metabolic activity has remained unclear. On the mitochondrial surface, Tom22 or Tom20 directs precursor import through the pore-forming subunit, Tom40. After emerging from the Tom40 channel, presequence-containing precursors engage with the presequence translocase of the inner membrane or reach the matrix directly as a permanent resident or are integrated into the membrane. Thus, the activity of the inner membrane translocase is tightly regulated by targeting signals in a yet undefined manner. For the first time, we show that testicular as well as adrenal mitochondrial metabolic activity is dependent on more than one protein, where Tim50 and SCC are equally important, and depends on the specific unfolding conformation necessary for SCC. Following mitochondrial import of SCC, the N-terminus is first cleaved rapidly and then slowly cleaved a second time. The unfolded protein is transported to the IMS, where the C-terminus is inserted into the TIM23 complex, resulting in a significantly unfolded protein to interact and associate with Tim50 for metabolic activity. Therefore, Tim50 is possibly playing a role of a key factor for SCC metabolic activity in addition to the co-factors ferrodoxin and ferrodoxin reductase.