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Structural changes in the oxygen-evolving complex of photosystem II induced by the S1 to S2 transition: A combined XRD and QM/MM study.

Askerka M, Wang J, Brudvig GW, Batista VS - Biochemistry (2014)

Bottom Line: The S1 → S2 transition of the oxygen-evolving complex (OEC) of photosystem II does not involve the transfer of a proton to the lumen and occurs at cryogenic temperatures.Therefore, it is commonly thought to involve only Mn oxidation without any significant change in the structure of the OEC.We find that the main structural change in the OEC is in the position of the dangling Mn and its coordination environment.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.

ABSTRACT
The S1 → S2 transition of the oxygen-evolving complex (OEC) of photosystem II does not involve the transfer of a proton to the lumen and occurs at cryogenic temperatures. Therefore, it is commonly thought to involve only Mn oxidation without any significant change in the structure of the OEC. Here, we analyze structural changes upon the S1 → S2 transition, as revealed by quantum mechanics/molecular mechanics methods and the isomorphous difference Fourier method applied to serial femtosecond X-ray diffraction data. We find that the main structural change in the OEC is in the position of the dangling Mn and its coordination environment.

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QM/MM S1 and S2 models and difference Fouriermaps. (A) Simulated S2-minus-S1 difference Fouriermaps calculated using the QM/MM S1 and S2 modelsand phases derived from multicrystal noncrystallographic symmetryaveraging (see the text for computational procedures and contour levels).The highest peak near the OEC results from the displacement of Mn4.(B) Comparison of the simulated S2-minus-S1 (frompanel A) and X-ray-observed S2-minus-S1 (frompanel C) difference Fourier maps with color codes according to panelsA and C. (C) Observed S2-minus-S1 differenceFourier maps calculated from ref (7).
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fig1: QM/MM S1 and S2 models and difference Fouriermaps. (A) Simulated S2-minus-S1 difference Fouriermaps calculated using the QM/MM S1 and S2 modelsand phases derived from multicrystal noncrystallographic symmetryaveraging (see the text for computational procedures and contour levels).The highest peak near the OEC results from the displacement of Mn4.(B) Comparison of the simulated S2-minus-S1 (frompanel A) and X-ray-observed S2-minus-S1 (frompanel C) difference Fourier maps with color codes according to panelsA and C. (C) Observed S2-minus-S1 differenceFourier maps calculated from ref (7).

Mentions: In this work, we re-examined the isomorphous difference Fouriermaps using our newly improved phases and compare the experimentaldensity difference maps to calculated density difference Fourier mapsderived from quantum mechanics/molecular mechanics (QM/MM) models.The analysis shows subtle but significant structural differences,including changes in the position of the dangling Mn (denoted hereMn4) and its coordination environment, induced by the S1 → S2 transition (Figure 1).


Structural changes in the oxygen-evolving complex of photosystem II induced by the S1 to S2 transition: A combined XRD and QM/MM study.

Askerka M, Wang J, Brudvig GW, Batista VS - Biochemistry (2014)

QM/MM S1 and S2 models and difference Fouriermaps. (A) Simulated S2-minus-S1 difference Fouriermaps calculated using the QM/MM S1 and S2 modelsand phases derived from multicrystal noncrystallographic symmetryaveraging (see the text for computational procedures and contour levels).The highest peak near the OEC results from the displacement of Mn4.(B) Comparison of the simulated S2-minus-S1 (frompanel A) and X-ray-observed S2-minus-S1 (frompanel C) difference Fourier maps with color codes according to panelsA and C. (C) Observed S2-minus-S1 differenceFourier maps calculated from ref (7).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230327&req=5

fig1: QM/MM S1 and S2 models and difference Fouriermaps. (A) Simulated S2-minus-S1 difference Fouriermaps calculated using the QM/MM S1 and S2 modelsand phases derived from multicrystal noncrystallographic symmetryaveraging (see the text for computational procedures and contour levels).The highest peak near the OEC results from the displacement of Mn4.(B) Comparison of the simulated S2-minus-S1 (frompanel A) and X-ray-observed S2-minus-S1 (frompanel C) difference Fourier maps with color codes according to panelsA and C. (C) Observed S2-minus-S1 differenceFourier maps calculated from ref (7).
Mentions: In this work, we re-examined the isomorphous difference Fouriermaps using our newly improved phases and compare the experimentaldensity difference maps to calculated density difference Fourier mapsderived from quantum mechanics/molecular mechanics (QM/MM) models.The analysis shows subtle but significant structural differences,including changes in the position of the dangling Mn (denoted hereMn4) and its coordination environment, induced by the S1 → S2 transition (Figure 1).

Bottom Line: The S1 → S2 transition of the oxygen-evolving complex (OEC) of photosystem II does not involve the transfer of a proton to the lumen and occurs at cryogenic temperatures.Therefore, it is commonly thought to involve only Mn oxidation without any significant change in the structure of the OEC.We find that the main structural change in the OEC is in the position of the dangling Mn and its coordination environment.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Yale University , New Haven, Connecticut 06520-8107, United States.

ABSTRACT
The S1 → S2 transition of the oxygen-evolving complex (OEC) of photosystem II does not involve the transfer of a proton to the lumen and occurs at cryogenic temperatures. Therefore, it is commonly thought to involve only Mn oxidation without any significant change in the structure of the OEC. Here, we analyze structural changes upon the S1 → S2 transition, as revealed by quantum mechanics/molecular mechanics methods and the isomorphous difference Fourier method applied to serial femtosecond X-ray diffraction data. We find that the main structural change in the OEC is in the position of the dangling Mn and its coordination environment.

Show MeSH
Related in: MedlinePlus