Download MendeleyMolecular basis of plastoquinone reduction in plant cytochrome b 6 f.
Pintscher, S., Pietras, R., Mielecki, B., Szwalec, M., Wojcik-Augustyn, A., Indyka, P., Rawski, M., Koziej, L., Jaciuk, M., Wazny, G., Glatt, S., Osyczka, A.(2024) Nat Plants 10: 1814-1825
- PubMed: 39362993
- DOI: https://doi.org/10.1038/s41477-024-01804-x
- Primary Citation of Related Structures:
9ES7, 9ES8, 9ES9 - PubMed Abstract:
A multi-subunit enzyme, cytochrome b 6 f (cytb 6 f), provides the crucial link between photosystems I and II in the photosynthetic membranes of higher plants, transferring electrons between plastoquinone (PQ) and plastocyanin. The atomic structure of cytb 6 f is known, but its detailed catalytic mechanism remains elusive. Here we present cryogenic electron microscopy structures of spinach cytb 6 f at 1.9 Å and 2.2 Å resolution, revealing an unexpected orientation of the substrate PQ in the haem ligand niche that forms the PQ reduction site (Q n ). PQ, unlike Q n inhibitors, is not in direct contact with the haem. Instead, a water molecule is coordinated by one of the carbonyl groups of PQ and can act as the immediate proton donor for PQ. In addition, we identify water channels that connect Q n with the aqueous exterior of the enzyme, suggesting that the binding of PQ in Q n displaces water through these channels. The structures confirm large movements of the head domain of the iron-sulfur protein (ISP-HD) towards and away from the plastoquinol oxidation site (Q p ) and define the unique position of ISP-HD when a Q p inhibitor (2,5-dibromo-3-methyl-6-isopropylbenzoquinone) is bound. This work identifies key conformational states of cytb 6 f, highlights fundamental differences between substrates and inhibitors and proposes a quinone-water exchange mechanism.
Organizational Affiliation:
Małopolska Centre of Biotechnology (MCB), Jagiellonian University, Kraków, Poland.
