Redesigning the QA binding site of Photosystem II allows reduction of exogenous quinones

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Redesigning the QA Binding Site of Photosystem II Allows Reduction of Exogenous Quinones, Nat. Commun., 8, 15274

 

The prospect of biophotovoltaics whereby organisms performing oxygenic photosynthesis are exploited to generate electric power emerged over the last decade. It consists in utilizing the remarkable characteristics of photosynthetic reaction centres to generate electrical power. The potentialities of natural photosystems rely on their very high maximum quantum efficiency. Yet, extracting electrons from these photosystems to generate a photocurrent requires the establishment of sustained flux that will be determined by the intrinsic rate constant of light-independent reactions. Currently, these kinetic limitations are such that the yield of biophotovoltaics is still far lower than the theoretical limit of conversion efficiency.

To circumvent these limitations, attempts were made to optimize the electrical connectivity between isolated photosystems and the electrode that eventually collects the reducing equivalents they produce under illumination. For instance, the ZnO-binding peptide was used to facilitate electron transfer from PSI to ZnO anodes when this peptide was linked to the PsaE subunit, which allows tight docking of PSI to the anode. Alternatively, single amino acid substitutions were made within photosystems to change their surface charge density and favour electron transfer to the electrode. As an example, the D1-K238 mutation on the stromal surface of PSII led to higher photocurrent in Synechocystis.

 

 

We aimed at establishing a proof-of-principle device that would use intact engineered unicellular algae—in the present case Chlamydomonas reinhardtii—to produce a photocurrent without compromising their ability to perform photosynthesis. Producing a photocurrent out of a living cell may of course be the result of many processes, which may be difficult to properly identify, in such a complex multimolecular and multicompartment context. In this respect, the 12 PSII mutant strains in this study provided very contrasting results, once screened for a preserved intrinsic photosynthetic activity and for their ability to transfer electron to DMBQ that would sustain a usable photocurrent. These successive screens lead us to retain one mutant that satisfied the two criteria above therefore standing as the corner stone of future development and improvement of photovoltaic devices along the above described strategy. This study also raises a number of issues worth further investigation…

 

Consultez le communiqué de presse associé à cet article : Des algues qui produisent de l'électricité !

 

Résumé: 

Nat. Commun., 8, 15274

 

Strategies to harness photosynthesis from living organisms to generate electrical power have long been considered, yet efficiency remains low. Here, we aimed to reroute photosynthetic electron flow in photosynthetic organisms without compromising their phototrophic properties. We show that 2,6-dimethyl-p-benzoquinone (DMBQ) can be used as an electron mediator to assess the efficiency of mutations designed to engineer a novel electron donation pathway downstream of the primary electron acceptor QA of Photosystem (PS) II in the green alga Chlamydomonas reinhardtii. Through the use of structural prediction studies and a screen of site-directed PSII mutants we show that modifying the environment of the QA site increases the reduction rate of DMBQ. Truncating the C-terminus of the PsbT subunit protruding in the stroma provides evidence that shortening the distance between QA and DMBQ leads to sustained electron transfer to DMBQ, as confirmed by chronoamperometry, consistent with a bypass of the natural QA°- to QB pathway.

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Redesigning the QA Binding Site of Photosystem II Allows Reduction of Exogenous Quinones

 

Han-Yi Fu, Daniel Picot, Yves Choquet, Guillaume Longatte, Adnan Sayegh, Jérôme Delacotte, Manon Guille-Collignon, Frédéric Lemaître, Fabrice Rappaport, and Francis-André Wollman

 

Nat. Commun., 8, 15274

 

DOI: 10.1038/ncomms15274