Amino Acid Residues That Influence the Binding of Manganese or Calcium to Photosystem II. 1. The Lumenal Interhelical Domains of the D1 Polypeptide

Abstract

To identify amino acid residues that ligate the manganese and calcium ions of photosystem II or that are otherwise crucial to water oxidation, site-directed mutations were constructed in the unicellular cyanobacterium Synechocystis sp. PCC 6803 at all conserved carboxylate, histidine, and tyrosine residues in the lumenal interhelical domains of the D1 polypeptide. Mutants with impaired photoautotrophic growth or oxygen evolution were characterized in vivo by measuring changes in the yield of variable chlorophyll a fluorescence after a saturating flash or brief illumination given in the presence of an electron-transfer inhibitor or following each in a series of saturating flashes given in the absence of inhibitor [Chu, H.-A., Nguyen, A. P., & Debus, R. J. (1994) Biochemistry 33, 6137-6149]. Mutants were also characterized after propagation in media having other cations substituted for calcium. We conclude that Asp-59 and Asp-61 may ligate calcium, that Asp-59, Asp-61, Glu-65, and His-92 influence the properties of the manganese cluster without significantly affecting its stability or ability to assemble, that Glu-189 plays an important structural role in maintaining the catalytic efficiency of the Mn cluster and partly influences the cluster's stability or ability to assemble, that His-92 and Glu-189 influence the binding of calcium, and that His-190 strongly influences the redox properties of the secondary electron donor, YZox, and either ligates manganese or serves as a crucial base or hydrogen bond donor. In addition, we conclude that Asp-170 may ligate manganese, but that its replacement with Val, Leu, or Ile causes structural perturbations that partly compensate for the loss of the carboxylate moiety.

No Evidence from FTIR Difference Spectroscopy That Glutamate-189 of the D1 Polypeptide Ligates a Mn Ion That Undergoes Oxidation during the S0 to S1, S1 to S2, or S2 to S3 Transitions in Photosystem II

“…This conclusion would be consistent with the earlier spectroscopic analyses of D1-Glu189 mutants (14,15,20), but presents another challenge: it requires that the proximity of D1-Glu189 to Mn in the X-ray crystallographic structural models be an artifact of the radiation-induced reduction of the Mn 4 cluster that occurred during the collection of the X-ray diffraction data. However, as noted earlier, recent X-ray absorption studies of PSII single crystals (21) and PSII membrane multilayers (22) show that the X-ray doses that were used in the crystallographic studies to irradiate the PSII crystals would have caused a surprisingly rapid reduction of the Mn 4 cluster's oxidized Mn(III/IV) ions to their fully reduced Mn(II) states and substantially modified the structure of the Mn 4 cluster.…”

Multifrequency electron spin-echo envelope modulation studies of nitrogen ligation to the manganese cluster of photosystem II

“…This argument for histidine ligation to the Mn cluster is in agreement with previous EPR and mutagenesis studies that show His332 is necessary for efficient photoassembly of the Mn cluster (Campell et al 2000), as well as proper S-state turnover (Chu et al 1995;Debus et al 2000;Allahverdiyeva et al 2004). Further evidence for His332 coordination is provided by ESEEM studies of the D1-H332E mutant (Debus et al 2001).…”

Tyrosine-Z in Oxygen-Evolving Photosystem II: A Hydrogen-Bonded Tyrosinate

“…From mutagenesis (88)(89)(90)(91) and modeling studies (14,92) of PSII it has been proposed that D1His190 is likely one hydrogen bond acceptor of Y Z . There are further hydrogen-bonding amino acid residues in close proximity to Y Z , namely Asp170 and Glu189 (81,98).…”