Hydrogen bond network analysis reveals the pathway for the proton transfer in the E-channel of T. thermophilus Complex I

• Published in: Biochimica et biophysica acta. Bioenergetics 2020-10, Vol.1861 (10), p.148240-148240, Article 148240
• Main Authors: Khaniya, Umesh, Gupta, Chitrak, Cai, Xiuhong, Mao, Junjun, Kaur, Divya, Zhang, Yingying, Singharoy, Abhishek, Gunner, M.R.
• Format: Article
• Language: English
• Subjects: Complex I; Grand Canonical Monte Carlo Simulations; Hydrogen bond network; Proton pumping; Proton transfer
• ISSN: 0005-2728; 1879-2650
• DOI: 10.1016/j.bbabio.2020.148240

Complex I, NADH-ubiquinone oxidoreductase, is the first enzyme in the mitochondrial and bacterial aerobic respiratory chain. It pumps four protons through four transiently open pathways from the high pH, negative, N-side of the membrane to the positive, P-side driven by the exergonic transfer of electrons from NADH to a quinone. Three protons transfer through subunits descended from antiporters, while the fourth, E-channel is unique. The path through the E-channel is determined by a network analysis of hydrogen bonded pathways obtained by Monte Carlo sampling of protonation states, polar hydrogen orientation and water occupancy. Input coordinates are derived from molecular dynamics trajectories comparing oxidized, reduced (dihydro) and no menaquinone-8 (MQ). A complex proton transfer path from the N- to the P-side is found consisting of six clusters of highly connected hydrogen-bonded residues. The network connectivity depends on the presence of quinone and its redox state, supporting a role for this cofactor in coupling electron and proton transfers. The N-side is more organized with MQ-bound complex I facilitating proton entry, while the P-side is more connected in the apo-protein, facilitating proton exit. Subunit Nqo8 forms the core of the E channel; Nqo4 provides the N-side entry, Nqo7 and then Nqo10 join the pathway in the middle, while Nqo11 contributes to the P-side exit. •One of the four protons pumped through Complex I (NADH-ubiquinone oxidoreductase), goes through a unique E-channel.•Combined Molecular Dynamics, Monte Carlo and network analysis finds a complex not linear E-channel proton path.•Six buried highly inter-connected clusters of polar and protonatable residues and waters are found.•The proton path connections respond to the presence and redox state of the substrate menaquinone.