Abstract
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 PSI I 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.