The structure of the photosystem I (PSI) complex from Synechocystis is determined, and reaction center subunits engineered to resemble a viral PSI are found to promote promiscuous electron acceptor properties.
In vivo evidence is provided indicating that Flv2/Flv4, together with Flv1/Flv3, mediate O2 photoreduction downstream of PSI in a highly coordinated manner.