Characteristics of Oxygen-Evolving System in Synechocystis Mutants
on C-Terminus of D1 Protein of Photosystem II:
(1) Growth, Activities, Protein Compositions, and Mn-Cluster

Abstract

We constructed and characterized Synechocystis mutants, in which Ala344 of D1 protein was replaced by glycine, valine, and aspartate (A344G, A344V, A344D) and His-tag was attached to CP47, to elucidate the role of C-terminus Ala344 of D1 protein as a putative ligand to Mn-cluster in PSII. Under moderate light conditions (50 μE m^-2s^-1), all the mutants grew photoautotrophically, however, A344G and A344D mutants could not grow photoautotrophically at increased light intensity of 200 μE m^-2s^-1. A344G and A344D mutants exhibited thermoluminescence Q-band (S₂Q_A^-) and B-band (S₂Q_B^-) at temperatures higher by 5^oC than those of the control strain. No change in protein compositions of the purified PSII particles were detected in the mutants. These results suggest that the Gly or Asp substitution affects the properties of Mn-cluster. To examine the effects of mutations on the structure of Mn-cluster, we are conducting EPR spectroscopic characterization of Mn-cluster.