Structural basis and regulation of the reductive stress response

Area of Science:

• Biochemistry
• Cellular Biology
• Molecular Biology

Background:

• Oxidative phosphorylation produces ATP but also reactive oxygen species (ROS).
• Reductive stress, a depletion of ROS, disrupts cellular signaling and is linked to diseases like cancer, diabetes, and cardiomyopathy.
• Cells degrade the mitochondrial protein FNIP1 to counteract reductive stress.

Purpose of the Study:

• To elucidate the mechanism by which the E3 ligase CUL2^FEM1B binds its target FNIP1 based on cellular redox state.
• To understand how this interaction is regulated in response to changing cellular environments.

Main Methods:

• Investigated the role of zinc in mediating the interaction between CUL2^FEM1B and FNIP1.
• Utilized genetic manipulation (gain-of-function mutation, gene deletion) to study the effects of CUL2^FEM1B and BEX family proteins.
• Examined the impact of FNIP1 ubiquitylation and degradation on cellular homeostasis.

Main Results:

• CUL2^FEM1B utilizes zinc as a molecular bridge to selectively bind reduced FNIP1 during reductive stress.
• BEX family proteins act as pseudosubstrate inhibitors, gating FNIP1 ubiquitylation and preventing premature degradation.
• Disruption of this zinc-dependent pathway, via FEM1B mutation or BEX deletion, leads to developmental abnormalities.

Conclusions:

• Zinc-dependent recruitment of reduced FNIP1 by CUL2^FEM1B is a critical mechanism for managing reductive stress.
• BEX proteins are essential regulators, preventing unwarranted ROS accumulation by controlling FNIP1 degradation.
• Tight regulation of this zinc-dependent reductive stress response is vital for maintaining cellular and organismal homeostasis.