Functional plasticity of AIF revealed by dimerization and CHCHD4 interaction states

Apoptosis-inducing factor is a mitochondrial flavoprotein that links redox metabolism to mitochondrial homeostasis through its interaction with the disulfide relay protein CHCHD4. Although NADH-dependent AIF dimerization has been proposed as the activated state mediating CHCHD4 engagement, whether it is strictly required for productive AIF-CHCHD4 function remains unclear. Here, combining cellular, biochemical and biophysical approaches, we show that disruption of the AIF dimer interface compromises oxidative phosphorylation, respiratory-chain organization and CHCHD4-dependent mitochondrial homeostasis, yet preserves partial AIF function. Our data reveal that the AIF-CHCHD4 system operates as a conformational dynamic redox module in which distinct AIF oligomeric and redox states sustain CHCHD4 activity with different efficiencies. Mechanistically, dimerization is coupled to NADH-dependent conformational changes that regulate coenzyme binding, charge-transfer complex stabilization and catalytic efficiency. In turn, CHCHD4 binding remodels AIF conformational and redox properties, partially compensating for defects in dimer stabilization or redox coupling. Consistently, a peptide derived from the CHCHD4 N-terminus partially restores redox function in a pathogenic AIF variant defective in dimer stabilization, supporting partner-assisted allosteric regulation as a potential therapeutic strategy.