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2. XFEL ðpµ½ PSII Ì³¹»\¢ðÍêÊÉCyfÉæéG}½ÍG}SÌ¯\îÆî¿Í Mn1D _Mn2C ª 2.7 Å C Mn1D _Mn3B ª 3.2 Å C
Mn1D _Mn4A ª 5.0 Å C Mn2C _Mn3B ª 2.7 Å C Mn2C _Mn4A ª5.2 ÅCMn3B_Mn4A ª2.9 Å ÆÈÁÄ¨èCSÄÌ Mn_Mn £ª SR \¢Æä×Ä0.1_0.2 Å ¸ÂZ­Ì\¢âÝìpª²­í¸©¸ÂÏ»·é±ÆÉæèiÈÁÄ¨èCEXAFS â_vZÌÊÆàÇ­êvµ½s·éB±Ì²­í¸©È\¢âÝìpÌÏ»ÆúËüiFig. 1(b)QÆjBêû Mn_Ca Ì£É¨¢ÄÍ Mn1D_

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Fig. 1ªð½@\(Color online) Atomic structure of the OEC by XFEL.
a, Electron density maps of the OEC. Grey, 2mFo_DFc map contoured at 7 sigma; brown, 2mFo_DFc map
contoured at 15 sigma; purple, mFo_DFc map contoured at 6 sigma. The mFo_DFc map was calculated after
introducing the manganese and calcium atoms but without the oxygen atoms and water molecules. Colour codes
for atoms: grey, manganese; green, calcium; cyan, oxo­oxygen; red, O5; blue, water. Numbers 1_4 in the cyan
spheres indicate O1_O4 atoms, and 1D, 2C, 3B and 4A indicate the four manganese ions. b, Mn_Mn distances in
the OEC (in Å). Numerals in the spheres indicate the valence of manganese atoms assigned in this work. c,Mn_
Ca distances in the OEC (in Å). d, Mn_O, Ca_O, Mn_water and Ca_water distances in the OEC (in Å).
Converted from Nature 517, 99 (2015).

Ca ª 3.5 Å C Mn2C _Ca ª 3.3 Å C Mn3B _Ca ª 3.4 Å C\¢Æär·éÆ Mn3B, Mn4A, Ca ©çÌ O5 ÖÌ

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Ì MniMn4A Ü½Í Mn1DjÆÍµÈ¢Æ¢¤C¶ª

O5 ª 2.2 Å C Mn4A _O5 ª 2.3 Å C Mn1D _O5 ª 2.7 Å C^\¢iO5 Ì¶¤ÉXy[XªÅ«éj

Ca_O5 ª2.5 Å ÆÈÁÄ¢½iFig. 1(d)QÆjB±êð SR¢7,14) ÉÈé±ÆCXFEL Ì\¢ÉÅàK·éÌÍ O5

é¢ÍE^\

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Fig. 2

(Color online) Jahn­Teller axes on Mn1D and Mn4A.
Converted from Nature 517, 99 (2015).

Ì´qíð OH| Æzèµ½êÅé±Æª¦³êÄ¢é15,16)B]ÁÄCMn4CaO5 NX^[Å©çêé Mn_
O5 Ì·¢Í OH| Æ Mn1D, Mn4A ÆÌÉR·é OEC Ì@\ÉÖAµ½ÁLÌ«¿Å

é±Æªl¦

çêéißQÆjBXFEL \¢É¨¢ÄCOEC ð\¬·élÂÌ Mn Í¢¸êàZzÊ\¢ÆÈÁÄ¨èC½ÏÌKh£Í
Mn1D ª 2.1 ÅCMn2C ª 2.0 ÅC Mn3B ª2.0 ÅC Mn4A
ª2.1 Å ÆÈÁÄ¢½BMn1D Æ Mn4A Ì½ÏKh£ª Mn2C Æ Mn3B æèà­µ·¢ÌÍCMn1D Ìñ

Fig. 3ÂÌzÊq O5 Æ D1 ^pN¿Ì342ÔÚÌAXpM(Color online) Possible mechanisms for the oxygen­evolving
reaction. Converted from Nature 517, 99 (2015).

cîÌ¤½ÌJ{__fCMn4A ÌñÂÌzÊq
O5 Æ W1 ÌûüÌKh£ª·­ÈÁÄ¢é½ßÅ

»µÄ O5 ÍêûÌ Mn Ì³Ìd×ª­ÈÁ½±ÆC¨

èC±ÌzÊqÌ·³É¨¯écÝÍ Jahn­Teller øÊæÑCJahn­Teller ²ÌÁ¸ÉæèC{4 Ì¿ðàÂ Mn

ÆÄÎêC{3 Ì¿ðÂ Mn ´qÉÁ¥IÈàÌÅ

Ì¤ÉÐ«ñ¹çêéB±ÌÆ«CMn4A Ì¿ª{4 ÉéiFig. 2 QÆjB±êçÌm©ÉîÃ«CäXÍ S1 óÔ

ÈêÎ O5 Í Mn4A Ì¤ÉÐ«ñ¹çê Mn3CaO4 ÌLÌlÂÌ Mn ´qÌ¿ªiMn1D, Mn2C, Mn3B, Mn4A)oÌªÍJ¢½\¢ðÆèC»ÌÊCMn1D Ì¤({3, {4, {4, {3jÅ

ÉXy[XªÅ«Ä S2 ÍE^\¢ÆÈéBtÉCMn1D

é±Æðñ¥µ½B±êÍÅßñ³ê½ OEC ðÍíµ½¬ Mn4CaO4 »¨É¨Ì¿ª{4 ÉÈêÎ O5 Í Mn1D Ì¤ÉÐ«ñ¹çê¯é Mn CIÌ¿Ìªz17) â EPR Æ_vZðp¢Mn3CaO4 ÌLÄ¾çê½ S2 óÔÌ Mn1D Ì¿ª{3 ÅÈé19)BÂÃ­ S3 óÔ¨æÑ S4 óÔÅÍC±ÌJ¢½X

éÆ¢¤ñ18) ÆàêvµÄ¢éBy[XÉVµ¢oÌªÌÂ¶½¶^\¢Ì S2 óÔÉªqªüè O5 Æ OO ð`¬·éB¶¬³ê½_fªqÍro³ê_f­¶SÍ S0 ó

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éBÂÃ­ S0 óÔ©ç S1 óÔÖÌJÚÉÆàÈ¢CO5

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ª OH| Åªqª O5 ÌÊuÖÆæèÜêèC»Ì»wíªq©çvgª²«æçêé±ÆÉæè O5 ÍÌéÂ\«ª¢±Æª¦´³ê½ÌÅCO5

OH| ÉÈèCS1 óÔÖàÇéB±êçÌêAÌ½@\ª_fªqÌ`¬ÉKvÈî¿ÌêÂðñµÄ¢é±Æ

Í_vZÌÊ20) C¨æÑCÅßÌdqXs¤ÂÉªl¦çêéB±êçÌm©©çæéÊ21) ÆàåûÅêvµÄ¢½Bªð½Ì@\ðñ¥µ½iFig. 3 QÆjBÜ¸CS1 óÔÉ¨¢ÄÍ Mn1D ¨æÑ Mn4A ª¯¶{3 Ì¿ðà¿C³çÉCJahn­TellerøÊÉæè Mn1D_O5 Æ Mn4A_O5 Í·¢£ðàÂBPSII Ì½SªêÂÌõqðzûµCMn4CaO5 NÓ«{¤ÍªRåwÌF÷C´

NÆmC»w¤Ì½cM¶mCãìmCºã¥mCRº X ^ [ © ç d q ð ê Â Ð « ² « C S2 ó Ô É È é Æ

b¾YmÆÌ¤¯¤ÅMn1Dµã°éB{¤ÍÈw¤ïÁÊi¤CáèiBjC

é¢Í Mn4A Ì¢¸ê©ª{4 Ì¿ðàÂB

180  úËõ July 2015 Vol.28 No.4

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úËõ July 2015 Vol.28 No.4  181

Radiation damage­free structure of photosystem
II revealed by an X­ray free electron laser
illuminates water splitting reaction mechanism
Michihiro SUGA

Graduate School of Natural Science and Technology/Photosynthesis ResearchCenter3_
1_1 Tsushima Naka, Okayama, 700_
8530, Japan

Fusamichi AKITA

Graduate School of Natural Science and Technology/Photosynthesis ResearchCenter3_
1_1 Tsushima Naka, Okayama, 700_
8530, Japan

Masaki YAMAMOTO

RIKEN SPring­8 Center
1_1_1 Kout Sayo, Hyogo, 679_
5148, Japan

Hideo AGORIKEN SPring­8 Center
1_
1_1 Kout Sayo, Hyogo, 679_5148, Japan

Jian­Ren SHEN

Graduate School of Natural Science and Technology/Photosynthesis ResearchCenter3_
1_1 Tsushima Naka, Okayama, 700_
8530, Japan

Abstract

Photosynthesis converts light energy into biologically useful chemical energy vital to life on Earth.
The initial reaction of photosynthesis takes place in photosystem II (PSII), a 700 kDa membraneprotein complex that catalyzes photo­oxidation of water into dioxygen through an S­state cycle ofthe oxygen evolving complex (OEC). The structure of PSII has been solved by X­ray diraction(XRD) at 1.9 Å resolution, which revealed that the OEC is a Mn4CaO5 cluster coordinated by awell­dened protein environment. However, extended X­ray absorption ne structure (EXAFS)
studies showed that the manganese atoms in the OEC are easily reduced by X­ray irradiation, andslight dierences were found in the Mn_Mn distances determined by XRD and EXAFS studies.
Here we report a radiation_damage free structure of PSII in the S1 state at a resolution of 1.95 Åusing femtosecond X_ray pulses of the SACLA facility and hundreds of large, highly isomorphous
PSII crystals. Compared with the structure from XRD, the OEC in the X_ray free electron laser(XFEL) structure has Mn_Mn distances that are shorter by 0.1_0.2 Å. Based on the XFEL struc­ture, the valences of each manganese atom were tentatively assigned as Mn1D ({3), Mn2C({4), Mn3B ({4) and Mn4A ({3) in the S1 state and that O5 is a hydroxide ion and may serve
as one of the substrate oxygen atoms. These ndings provide a structural basis for the mechan­
ism of oxygen evolution, and we expect that this structure will provide a blueprint for the design ofarticial catalysts for water oxidation.

182  úËõ July 2015 Vol.28 No.4