Crystal Structure of PsbQ from Synechocystis sp. PCC 6803 at 1.8 Å: Implications for Binding and Function in Cyanobacterial Photosystem II

In Synechocystis sp. PCC 6803, PsbQ is associated with photosystem II (PSII) complexes with the highest activity and stability. However, this subunit is not found in PSII X-ray crystallographic structures from Thermosynechococcus elongatus or Thermosynechococcus vulcanus. We present the crystal structure of cyanobacterial PsbQ determined in the presence and absence of Zn²⁺. The protein has a well-defined helical core, containing four helices arranged in an up−down−up−down fold. A conserved potential interaction site composed of a divalent metal binding site and adjacent hydrophobic pocket has been identified.