Ophiobolin A Covalently Targets Mitochondrial Complex IV Leading to Metabolic Collapse in Cancer Cells

Ophiobolin A (OPA) is a sesterterpenoid fungal natural product with broad anticancer activity. While OPA possesses multiple electrophilic moieties that can covalently react with nucleophilic amino acids on proteins, the proteome-wide targets and mechanism of OPA remain poorly understood in many contexts. In this study, we used covalent chemoproteomic platforms to map the proteome-wide reactivity of the OPA in a highly sensitive lung cancer cell line. Among several proteins that OPA engaged, we focused on two targets: lysine-72 of cytochrome c oxidase subunit 5A (COX5A) and cysteine-53 of mitochondrial hypoxia induced gene 1 domain family member 2A (HIGD2A). These two subunit proteins are part of complex IV (cytochrome C oxidase) within the electron transport chain and contributed significantly to the antiproliferative activity of OPA. OPA activated mitochondrial respiration in a COX5A- and HIGD2A-dependent manner, leading to an initial spike in mitochondrial ATP and heightened mitochondrial oxidative stress. OPA compromised mitochondrial membrane potential, ultimately leading to ATP depletion. We have used chemoproteomic strategies to discover a unique anticancer mechanism of OPA through activation of complex IV leading to compromised mitochondrial energetics and rapid cell death.