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Proc Natl Acad Sci U S A. 2019 Oct 22;116(43):21907-21913. doi: 10.1073/pnas.1909644116. Epub 2019 Oct 8.

A novel chlorophyll protein complex in the repair cycle of photosystem II.

Author information

1
Department of Biology, Washington University in St. Louis, St. Louis, MO 63130.
2
Center for Solar Energy & Energy Storage, Department of Energy, Environmental, & Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130.
3
Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110.
4
Department of Physics, Washington University in St. Louis, St. Louis, MO 63130.
5
Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130.
6
Department of Biology, Washington University in St. Louis, St. Louis, MO 63130; Pakrasi@wustl.edu.

Abstract

In oxygenic photosynthetic organisms, photosystem II (PSII) is a unique membrane protein complex that catalyzes light-driven oxidation of water. PSII undergoes frequent damage due to its demanding photochemistry. It must undergo a repair and reassembly process following photodamage, many facets of which remain unknown. We have discovered a PSII subcomplex that lacks 5 key PSII core reaction center polypeptides: D1, D2, PsbE, PsbF, and PsbI. This pigment-protein complex does contain the PSII core antenna proteins CP47 and CP43, as well as most of their associated low molecular mass subunits, and the assembly factor Psb27. Immunoblotting, mass spectrometry, and ultrafast spectroscopic results support the absence of a functional reaction center in this complex, which we call the "no reaction center" complex (NRC). Analytical ultracentrifugation and clear native PAGE analysis show that NRC is a stable pigment-protein complex and not a mixture of free CP47 and CP43 proteins. NRC appears in higher abundance in cells exposed to high light and impaired protein synthesis, and genetic deletion of PsbO on the PSII luminal side results in an increased NRC population, indicative that NRC forms in response to photodamage as part of the PSII repair process. Our finding challenges the current model of the PSII repair cycle and implies an alternative PSII repair strategy. Formation of this complex may maximize PSII repair economy by preserving intact PSII core antennas in a single complex available for PSII reassembly, minimizing the risk of randomly diluting multiple recycling components in the thylakoid membrane following a photodamage event.

KEYWORDS:

mass spectrometry; photosynthesis; protein turnover; repair cycle; ultrafast spectroscopy

PMID:
31594847
PMCID:
PMC6815111
[Available on 2020-04-08]
DOI:
10.1073/pnas.1909644116

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