Modified EPR spectra of the tyrosineD radical in photosystem II in site-directed mutants of Synechocystis sp. PCC 6803

Identification of side chains in the immediate vicinity of tyrosineD on the D2 protein

Cecilia Tommos, Lars Davidsson, Bengt Svensson, Cathy Madsen, Willem Vermaas, Stenbjörn Styring

Research output: Contribution to journalArticle

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Abstract

The oxidizing side of photosystem II contains two redox-active tyrosyl side chains, Tyrz and TyrD, and a cluster of Mn atoms involved in water oxidation. The structural environment of these components is unknown, and with computer-assisted modeling we have created a three-dimensional model for the structures around TyrZ and TyrD [Svensson et al. (1990) EMBO J. 9, 2051-2059]. Both tyrosines are proposed to form hydrogen bonds to nearby histidine residues (for Synechocystis 6803, these are His190 on the D1 and His189 on the D2 proteins). We have tested this proposal by electron paramagnetic resonance (EPR) spectroscopy of TyrD ox in mutants of the cyanobacterium Synechocystis 6803 carrying site-directed mutations in the D2 protein. In two mutants, where His189 of the D2 protein is changed to either Tyr or Leu, the normal EPR spectrum from TyrD ox is replaced by narrow, structureless radical signals with g-values similar to that of TyrD ox (g ≈ 2.0050). The new radicals copurify with photosystem II, are dark-stable, destabilized by elevated pH, and light-inducible, and originate from radicals formed by oxidation. These properties are similar to those of normal TyrD ox, and we assign the new spectra to TyrD ox in an altered environment induced by the point mutation in His189. In a third mutant, where Gln164 of the D2 protein was mutated to Leu, we also observed a modified EPR spectrum from TyrD ox. This is also consistent with the model in which this residue is found in the immediate vicinity of TyrD ox. Thus the results provide experimental evidence supporting essential aspects of the structural model.

Original languageEnglish (US)
Pages (from-to)5436-5441
Number of pages6
JournalBiochemistry
Volume32
Issue number20
StatePublished - 1993

Fingerprint

Synechocystis
Photosystem II Protein Complex
Electron Spin Resonance Spectroscopy
Paramagnetic resonance
Proteins
Oxidation
Structural Models
Cyanobacteria
Point Mutation
Histidine
Oxidation-Reduction
Tyrosine
Hydrogen
Spectrum Analysis
Hydrogen bonds
Spectroscopy
Light
Atoms
Mutation
Water

ASJC Scopus subject areas

  • Biochemistry

Cite this

Modified EPR spectra of the tyrosineD radical in photosystem II in site-directed mutants of Synechocystis sp. PCC 6803 : Identification of side chains in the immediate vicinity of tyrosineD on the D2 protein. / Tommos, Cecilia; Davidsson, Lars; Svensson, Bengt; Madsen, Cathy; Vermaas, Willem; Styring, Stenbjörn.

In: Biochemistry, Vol. 32, No. 20, 1993, p. 5436-5441.

Research output: Contribution to journalArticle

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title = "Modified EPR spectra of the tyrosineD radical in photosystem II in site-directed mutants of Synechocystis sp. PCC 6803: Identification of side chains in the immediate vicinity of tyrosineD on the D2 protein",
abstract = "The oxidizing side of photosystem II contains two redox-active tyrosyl side chains, Tyrz and TyrD, and a cluster of Mn atoms involved in water oxidation. The structural environment of these components is unknown, and with computer-assisted modeling we have created a three-dimensional model for the structures around TyrZ and TyrD [Svensson et al. (1990) EMBO J. 9, 2051-2059]. Both tyrosines are proposed to form hydrogen bonds to nearby histidine residues (for Synechocystis 6803, these are His190 on the D1 and His189 on the D2 proteins). We have tested this proposal by electron paramagnetic resonance (EPR) spectroscopy of TyrD ox in mutants of the cyanobacterium Synechocystis 6803 carrying site-directed mutations in the D2 protein. In two mutants, where His189 of the D2 protein is changed to either Tyr or Leu, the normal EPR spectrum from TyrD ox is replaced by narrow, structureless radical signals with g-values similar to that of TyrD ox (g ≈ 2.0050). The new radicals copurify with photosystem II, are dark-stable, destabilized by elevated pH, and light-inducible, and originate from radicals formed by oxidation. These properties are similar to those of normal TyrD ox, and we assign the new spectra to TyrD ox in an altered environment induced by the point mutation in His189. In a third mutant, where Gln164 of the D2 protein was mutated to Leu, we also observed a modified EPR spectrum from TyrD ox. This is also consistent with the model in which this residue is found in the immediate vicinity of TyrD ox. Thus the results provide experimental evidence supporting essential aspects of the structural model.",
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AU - Davidsson, Lars

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AU - Vermaas, Willem

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