Abstract
Biological energy conversion is driven by efficient enzymes that capture, store and transfer protons and electrons across large distances. Recent advances in structural biology have provided atomic-scale blueprints of these types of remarkable molecular machinery, which together with biochemical, biophysical and computational experiments allow us to derive detailed energy transduction mechanisms for the first time. Here, I present one of the most intricate and least understood types of biological energy conversion machinery, the respiratory complex I, and how its redox-driven proton-pump catalyses charge transfer across approximately 300 Å distances. After discussing the functional elements of complex I, a putative mechanistic model for its action-at-a-distance effect is presented, and functional parallels are drawn to other redox- and light-driven ion pumps.
Highlights
Energy conversion in nature is driven by efficient enzymes that catalyse elementary transfers of protons and electrons, or proton-coupled electron transfer (PCET) reactions [1,2,3,4]
Two main PCET pathways establish the bioenergetic basis of all life forms: the light-driven PCET of photosynthesis and the chemically driven PCET of respiratory chains
Molecular oxygen (O2), which is released as a ‘waste’ product from photosynthesis, powers respiratory chains of mitochondria and aerobic bacteria, where the electrons extracted from foodstuffs, catalyse proton transfer reactions across biological membranes [6,7,8]
Summary
Energy conversion in nature is driven by efficient enzymes that catalyse elementary transfers of protons and electrons, or proton-coupled electron transfer (PCET) reactions [1,2,3,4]. Complex I can catalyse QH2 oxidation and reverse electron transfer by employing an external pH gradient that reduces NADþ into NADH [29,30] Such operation modes are relevant under certain physiological conditions, such as hypoxia or ischaemia [31], where CcO cannot thermodynamically drive the electron transport chain. Owing to this reversibility, mutation of residues involved in proton pumping in distant membrane-bound subunits (NuoL/Nqo12/ND5) leads to the inhibition of the Q-reduction activity [32,33]. A mechanistic model that could explain central parts of the long-range proton–electron transfer process is presented
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