Crystal structure of photosystem i monomer from synechocystis PCC 6803

A single histidine addition to the C-terminus of PsaL of Synechocystis sp. PCC 6803 was previously reported by our lab to shift the trimer-to-monomer ratio of PSI in favor of the monomeric form. P700 re-reduction and NADP ⁺ photo-reduction measurements of the PsaL ^HIS strain show no effect on PSI activity in comparison to the WT trimeric PSI. Crystal structure of the PsaL ^HIS monomeric PSI reveals several alterations that occurred in the trimerisation site of PSI, primarily a deformation of the C-terminus of PsaL and loss of chlorophyll a and β-carotene molecules.