Recent advances in the structural diversity of reaction centers

Christopher J Gisriel,Chihiro Azai,Tanai Cardona

doi:10.1007/s11120-021-00857-9

Christopher J Gisriel, Chihiro Azai + Show 1 more

Open Access

https://doi.org/10.1007/s11120-021-00857-9

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Abstract

Photosynthetic reaction centers (RC) catalyze the conversion of light to chemical energy that supports life on Earth, but they exhibit substantial diversity among different phyla. This is exemplified in a recent structure of the RC from an anoxygenic green sulfur bacterium (GsbRC) which has characteristics that may challenge the canonical view of RC classification. The GsbRC structure is analyzed and compared with other RCs, and the observations reveal important but unstudied research directions that are vital for disentangling RC evolution and diversity. Namely, (1) common themes of electron donation implicate a Ca2+ site whose role is unknown; (2) a previously unidentified lipid molecule with unclear functional significance is involved in the axial ligation of a cofactor in the electron transfer chain; (3) the GsbRC features surprising structural similarities with the distantly-related photosystem II; and (4) a structural basis for energy quenching in the GsbRC can be gleaned that exemplifies the importance of how exposure to oxygen has shaped the evolution of RCs. The analysis highlights these novel avenues of research that are critical for revealing evolutionary relationships that underpin the great diversity observed in extant RCs.

Highlights

Reaction center (RC) proteins are at the heart of photosynthesis
Within a single protein complex, light excites antenna pigments and energy is transferred to the electron transfer (ET) domain of the RC where charge separation results in the transfer of electrons through a series of cofactors arranged in a gradient of potential energy (Blankenship 2008)
Electrons are donated to cofactors that diffuse away from the RC, reducing equivalents that fuel metabolism, and electron donors reduce the oxidized RC to poise it for another charge separation event

Summary

Introduction

Reaction center (RC) proteins are at the heart of photosynthesis. Within a single protein complex, light excites antenna pigments and energy is transferred to the electron transfer (ET) domain of the RC where charge separation results in the transfer of electrons through a series of cofactors arranged in a gradient of potential energy (Blankenship 2008). As with Acc, A 0 in the GsbRC exhibits a large hydrophobic residue near the C3 position, PscA-Phe625, that is not present in either the HbRC or PSI, suggesting that the Phe confers selectivity for Chl a rather than the bulk BChl a in this site

Results

Conclusion