Removal of Photosystem I Subunit PsaE Leads to Photosynthetic Hydrogen Production in a Cyanobacterial PsaF-HoxYH Fusion Strain.

Photosynthetic hydrogen (photoH2) production is a promising approach for the utilisation of solar energy. Fusion of a hydrogenase (H2ase) to photosystem I (PSI) provides a direct light-driven route for photoH2 generation. We established the lateral transmembrane subunit PsaF of PSI as a new fusion partner for the NiFe-hydrogenase (HoxYH) in the cyanobacterium Synechocystis sp. PCC 6803. Gradual reduction of PsaC expression in a PsaF-HoxYH strain was established to access the most redox negative FeS-cluster FX of PSI, but this did not result in photoH2 production. In another approach PSI subunit PsaE was identified as a potential steric hindrance in the psaF-hoxYH strain to electron transfer between the FeS-cluster FB cluster in PSI and HoxYH. Consistent with this, deletion of PsaE in psaF-hoxYH led to successful photoH2 production. Our results identify PsaF as a viable and structurally favourable anchor providing a new strategy for the engineering of photobiological H2-production systems.