Generating dihydrogen by tethering an [FeFe]hydrogenase via a molecular wire to the A/A sites of photosystem I.

Photosystem I complexes from the menB deletion mutant of Synechocystis sp. PCC 6803 were previously wired to a Pt nanoparticle via a molecular wire consisting of 15-(3-methyl-1,4-naphthoquinone-2-yl)]pentadecyl sulfide. In the presence of a sacrificial electron donor and an electron transport mediator, the PS I-NQ(CH)S-Pt nanoconstruct generated dihydrogen at a rate of 44.3 µmol of H mg Chl h during illumination at pH 8.3. The menB deletion strain contains an interruption in the biosynthetic pathway of phylloquinone, which results in the presence of a displaceable plastoquinone-9 in the A/A sites. The synthesized quinone contains a headgroup identical to the native phylloquinone along with a 15-carbon long tail that is terminated in a thiol. The thiol on the molecular wire is used to bind the Pt nanoparticle. In this short communication, we replaced the Pt nanoparticle with an [FeFe]Hase variant from Clostridium acetobutylicum that contains an exposed iron on the distal [4Fe-4S] cluster afforded by mutating the surface exposed Cys97 residue to Gly. The thiol on the molecular wire is then used to coordinate the corner iron atom of the iron-sulfur cluster. When all three components are combined and illuminated in the presence of a sacrificial electron donor and an electron transport mediator, the PS I-NQ(CH)S-[FeFe]Hase nanoconstruct generated dihydrogen at a rate of 50.3 ± 9.96 μmol of H mg Chl h during illumination at pH 8.3. This successful in vitro experiment sets the stage for assembling a PS I-NQ(CH)S-[FeFe]Hase nanoconstruct in vivo in the menB mutant of Synechocystis sp. PCC 6803.