Probing the effect of mutations of asparagine 181 in the D1 subunit of photosystem II

Ravi Pokhrel, Richard J. Debus, Gary W Brudvig

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Efficient proton removal from the oxygen-evolving complex (OEC) of photosystem II (PSII) and activation of substrate water molecules are some of the key aspects optimized in the OEC for high turnover rates. The hydrogen-bonding network around the OEC is critical for efficient proton transfer and for tuning the position and pKa values of the substrate water/hydroxo/oxo molecules. The D1-N181 residue is part of the hydrogen-bonding network on the active face of the OEC. D1-N181 is also associated with the chloride ion in the D2-K317 site and is one of the residues closest to a putative substrate water molecule bound as a terminal ligand to Mn4. We studied the effect of the D1-N181A and D1-N181S mutations on the water oxidation chemistry at the OEC. PSII core complexes isolated from the D1-N181A and D1-N181S mutants have steady-state O2 evolution rates lower than those of wild-type PSII core complexes. Fourier transform infrared spectroscopy indicates slight perturbations of the hydrogen-bonding network in D1-N181A and D1-N181S PSII core complexes, similar to the effects of some other mutations in the same region, but to a lesser extent. Unlike in wild-type PSII core complexes, a g = 4 signal was observed in the S2-state EPR spectra of D1-N181A and D1-N181S PSII core complexes in addition to the normal g = 2 multiline signal. The S-state cycling of D1-N181A and D1-N181S PSII core complexes was similar to that of wild-type PSII core complexes, whereas the O2-release kinetics of D1-N181A and D1-N181S PSII core complexes were much slower than the O2-release kinetics of wild-type PSII core complexes. On the basis of these results, we conclude that proton transfer is not compromised in the D1-N181A and D1-N181S mutants but that the O-O bond formation step is retarded in these mutants.

Original languageEnglish
Pages (from-to)1663-1672
Number of pages10
JournalBiochemistry
Volume54
Issue number8
DOIs
Publication statusPublished - Mar 3 2015

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Photosystem II Protein Complex
Asparagine
Mutation
Oxygen
Hydrogen Bonding
Protons
Hydrogen bonds
Proton transfer
Water
Molecules
Substrates
Kinetics
Fourier Transform Infrared Spectroscopy
Paramagnetic resonance
Chlorides
Reactive Oxygen Species
Tuning
Chemical activation
Ions
Ligands

ASJC Scopus subject areas

  • Biochemistry
  • Medicine(all)

Cite this

Probing the effect of mutations of asparagine 181 in the D1 subunit of photosystem II. / Pokhrel, Ravi; Debus, Richard J.; Brudvig, Gary W.

In: Biochemistry, Vol. 54, No. 8, 03.03.2015, p. 1663-1672.

Research output: Contribution to journalArticle

Pokhrel, Ravi ; Debus, Richard J. ; Brudvig, Gary W. / Probing the effect of mutations of asparagine 181 in the D1 subunit of photosystem II. In: Biochemistry. 2015 ; Vol. 54, No. 8. pp. 1663-1672.
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AB - Efficient proton removal from the oxygen-evolving complex (OEC) of photosystem II (PSII) and activation of substrate water molecules are some of the key aspects optimized in the OEC for high turnover rates. The hydrogen-bonding network around the OEC is critical for efficient proton transfer and for tuning the position and pKa values of the substrate water/hydroxo/oxo molecules. The D1-N181 residue is part of the hydrogen-bonding network on the active face of the OEC. D1-N181 is also associated with the chloride ion in the D2-K317 site and is one of the residues closest to a putative substrate water molecule bound as a terminal ligand to Mn4. We studied the effect of the D1-N181A and D1-N181S mutations on the water oxidation chemistry at the OEC. PSII core complexes isolated from the D1-N181A and D1-N181S mutants have steady-state O2 evolution rates lower than those of wild-type PSII core complexes. Fourier transform infrared spectroscopy indicates slight perturbations of the hydrogen-bonding network in D1-N181A and D1-N181S PSII core complexes, similar to the effects of some other mutations in the same region, but to a lesser extent. Unlike in wild-type PSII core complexes, a g = 4 signal was observed in the S2-state EPR spectra of D1-N181A and D1-N181S PSII core complexes in addition to the normal g = 2 multiline signal. The S-state cycling of D1-N181A and D1-N181S PSII core complexes was similar to that of wild-type PSII core complexes, whereas the O2-release kinetics of D1-N181A and D1-N181S PSII core complexes were much slower than the O2-release kinetics of wild-type PSII core complexes. On the basis of these results, we conclude that proton transfer is not compromised in the D1-N181A and D1-N181S mutants but that the O-O bond formation step is retarded in these mutants.

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