Redox-Activated Proton Transfer through a Redundant Network in the Q_o Site of Cytochrome bc₁

Author(s)

Arantes, Guilherme M.

• Document type: Journal article
• Source: JOURNAL OF CHEMICAL INFORMATION AND MODELING; v. 65, n. 5, p. 10-pg., 2025-02-26.

Abstract

Proton translocation catalyzed by cytochrome bc 1 (respiratory complex III) during coenzyme-Q redox cycling is a critical bioenergetic process, yet its detailed molecular mechanism remains incompletely understood. In this study, the energetics of the long-range proton transfers through multiple proton-conducting wires in the Qo site of the bc 1 complex was investigated computationally using hybrid QM/MM simulations and a specialized reaction coordinate. Key reactive groups and proton transfer mechanisms were characterized, confirming the propionate-A group of heme b L as a plausible proton acceptor. Upon coenzyme-Q oxidation, a Grotthuss hopping mechanism is activated, facilitating proton transfer along three distinct pathways with comparable barriers and stability. These pathways operate redundantly, forming a robust proton-conducting network, and account for the unusual experimental behavior observed in single-point mutations. Energetic analyses exclude charged closed-shell species as likely intermediates and propose a reaction sequence for coenzyme-Q oxidation proceeding as QH2 -> QH center dot -> Q0, either via coupled proton-electron transfers or stepwise mechanisms involving open-shell intermediates. These findings elucidate mechanistic details of the Q-cycle and improve our understanding of the catalytic reactions supporting redox-activated proton transfer in respiratory enzymes. (AU)

• FAPESP's process: 23/00934-5 - Computational methodologies for simulation of proton-coupled electron transfer in biomolecules
• Grantee: Guilherme Menegon Arantes
• Support Opportunities: Regular Research Grants