RESUMEN
Plant photosystem I (PSI) consists of at least 13 nuclear-encoded and 4 chloroplast-encoded subunits that together act as a sunlight-driven oxidoreductase. Here we report the structure of a PSI assembly intermediate that we isolated from greening oat seedlings. The assembly intermediate shows an absence of at least eight subunits, including PsaF and LHCI, and lacks photoreduction activity. The data show that PsaF is a regulatory checkpoint that promotes the assembly of LHCI, effectively coupling biogenesis to function.
Asunto(s)
Complejo de Proteína del Fotosistema I , Complejo de Proteína del Fotosistema I/metabolismo , Avena/metabolismo , Avena/genética , Proteínas de Plantas/metabolismo , Proteínas de Plantas/genética , Complejos de Proteína Captadores de Luz/metabolismo , Complejos de Proteína Captadores de Luz/genética , Plantones/genética , Plantones/metabolismoRESUMEN
Photosystem I is defined as plastocyanin-ferredoxin oxidoreductase. Taking advantage of genetic engineering, kinetic analyses and cryo-EM, our data provide novel mechanistic insights into binding and electron transfer between PSI and Pc. Structural data at 2.74â Å resolution reveals strong hydrophobic interactions in the plant PSI-Pc ternary complex, leading to exclusion of water molecules from PsaA-PsaB/Pc interface once the PSI-Pc complex forms. Upon oxidation of Pc, a slight tilt of bound oxidized Pc allows water molecules to accommodate the space between Pc and PSI to drive Pc dissociation. Such a scenario is consistent with the six times larger dissociation constant of oxidized as compared with reduced Pc and mechanistically explains how this molecular machine optimized electron transfer for fast turnover.
Asunto(s)
Chlamydomonas reinhardtii/metabolismo , Interacciones Hidrofóbicas e Hidrofílicas , Complejo de Proteína del Fotosistema I/química , Complejo de Proteína del Fotosistema I/metabolismo , Plastocianina/química , Plastocianina/metabolismo , Sitios de Unión , Transporte de Electrón , Cinética , Modelos Moleculares , Oxidación-Reducción , Unión Proteica , Conformación ProteicaRESUMEN
The ability of photosynthetic organisms to use sunlight as a sole source of energy is endowed by two large membrane complexes-photosystem I (PSI) and photosystem II (PSII). PSI and PSII are the fundamental components of oxygenic photosynthesis, providing oxygen, food and an energy source for most living organisms on Earth. Currently, high-resolution crystal structures of these complexes from various organisms are available. The crystal structures of megadalton complexes have revealed excitation transfer and electron-transport pathways within the various complexes. PSI is defined as plastocyanin-ferredoxin oxidoreductase but a high-resolution structure of the entire triple supercomplex is not available. Here, using a new cryo-electron microscopy technique, we solve the structure of native plant PSI in complex with its electron donor plastocyanin and the electron acceptor ferredoxin. We reveal all of the contact sites and the modes of interaction between the interacting electron carriers and PSI.