Mitochondria-endoplasmic reticulum crosstalk in apoptosis: The interactions of cytochrome c with monooxygenase and its reductase.

The crosstalk between endoplasmic reticulum and mitochondria is of significance in apoptosis, in which cytochrome b (Cyt b) is thought to be a major target for cytochrome c (Cyt c) upon its release from the mitochondria. In the absence of Cyt b, the role of interactions of Cyt c with CYP-dependent monooxygenase system in apoptotic regulation was explored in this study. NADPH-dependent and Cyt c-induced formation of reactive oxygen species (ROS) and NADPH-independent Cyt c unfolding were revealed. With the aid of a CPR inhibitor and CYP antibodies, the interactions among Cyt c, cytochrome P450 reductase (CPR) and cytochrome P450 (CYP) are evidenced, which are found crucial for monooxygenase-derived ROS formation. The underlying structural basis of Cyt c-CYP complex was unveiled by molecular dynamics simulations. This study provides novel insights into how Cyt c regulates ROS formation through the interactions with CPR and CYP, and is implicated for a deeper understanding of the regulation mechanism in the mitochondria-endoplasmic reticulum apoptotic pathway.