Structure of CyanoP at 2.8 Å: Implications for the Evolution and Function of the PsbP Subunit of Photosystem II

We present here the crystal structure of CyanoP (Tlr2075) from Thermosynechococcus elongatus at 2.8 angstrom. CyanoP is a substoichiometric component of the isolated cyanobacterial Photosystem II (PSII) complex, distantly related to the PsbP extrinsic subunit of the oxygen-evolving P S I I complex in higher plants and green algae. Despite the relatively low degree of sequence similarity, we have found that CyanoP adopts the same beta-sandwich fold as higher-plant PsbP and contains a well-conserved metal (zinc)binding site that is also present in plant PsbP. Our results support the idea that CyanoP represents the basal structural fold of the PsbP superfamily.