Helix–strand interaction regulates stability and aggregation of the human mitochondrial membrane protein channel VDAC3

Abstract

Voltage-dependent anion channels (VDACs) are β-sheet–rich transmembrane β-barrels that are vital for metabolite transport across the mitochondrial membrane. Under cellular stress, human VDACs hetero-oligomerize and coaggregate with proteins that can form amyloidogenic and neurodegenerative deposits, implicating a role for VDACs in proteotoxicity. However, whether VDACs possess intrinsic interaction sites that can lead to protein aggregation is not known. Here, we couple a systematic thiol replacement strategy with far-UV circular dichroism spectropolarimetry and UV scattering spectroscopy to map aggregation-prone regions of human VDACs, using isoform 3 as our model VDAC. We show that the region comprising strands β7–β9 is highly aggregation prone. Further, we find that an α1–β7–β9 interaction (involving the hVDAC3 N-terminal α1 helix) can lower protein aggregation, whereas perturbations of this interaction promote VDAC aggregation. We also show that hVDAC3 aggregation proceeds via a partially unfolded structure. Our findings allow us to propose a plausible mechanism for the role of human VDACs in forming proteotoxic aggregates in the cell. The key target sites on VDACs—strands β7–β9—may be useful for developing VDAC aggregation inhibitors.