18O Isotope Exchange Measurements Reveal that Calcium Is Involved in the Binding of One Substrate-Water Molecule to the Oxygen-Evolving Complex in Photosystem II

Biochemistry ◽  
2003 ◽  
Vol 42 (20) ◽  
pp. 6209-6217 ◽  
Author(s):  
Garth Hendry ◽  
Tom Wydrzynski
Keyword(s):  
Photosystem Ii ◽  
Water Molecule ◽  
Isotope Exchange ◽  
Oxygen Evolving Complex ◽  
18O Isotope Exchange ◽  
18O Isotope ◽  
Oxygen Evolving

scholarly journals Investigation of substrate water interactions at the high-affinity Mn site in the photosystem II oxygen-evolving complex

2007 ◽  
Vol 363 (1494) ◽  
pp. 1229-1235 ◽  
Author(s):  
Sonita Singh ◽  
Richard J Debus ◽  
Tom Wydrzynski ◽  
Warwick Hillier
Keyword(s):  
Hydrogen Bonding ◽  
Photosystem Ii ◽  
Exchange Rates ◽  
Isotope Exchange ◽  
Water Molecules ◽  
Oxygen Evolving Complex ◽  
Wild Type ◽  
High Affinity ◽  
O Isotope ◽  
Oxygen Evolving

18 O isotope exchange measurements of photosystem II (PSII) in thylakoids from wild-type and mutant Synechocystis have been performed to investigate binding of substrate water to the high-affinity Mn 4 site in the oxygen-evolving complex (OEC). The mutants investigated were D1-D170H, a mutation of a direct ligand to the Mn 4 ion, and D1-D61N, a mutation in the second coordination sphere. The substrate water 18 O exchange rates for D61N were found to be 0.16±0.02 s −1 and 3.03±0.32 s −1 for the slow and fast phases of exchange, respectively, compared with 0.47±0.04 s −1 and 19.7±1.3 s −1 for the wild-type. The D1-D170H rates were found to be 0.70±0.16 s −1 and 24.4±4.6 s −1 and thus are almost within the error limits for the wild-type rates. The results from the D1-D170H mutant indicate that the high-affinity Mn 4 site does not directly bind to the substrate water molecule in slow exchange, but the binding of non-substrate water to this Mn ion cannot be excluded. The results from the D61N mutation show an interaction with both substrate water molecules, which could be an indication that D61 is involved in a hydrogen bonding network with the substrate water. Our results provide limitations as to where the two substrate water molecules bind in the OEC of PSII.

scholarly journals Structural Changes in the Acceptor Site of Photosystem II upon Ca2+/Sr2+ Exchange in the Mn4CaO5 Cluster Site and the Possible Long-Range Interactions

Biomolecules ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 371
Author(s):  
Koua
Keyword(s):  
Crystal Structure ◽  
Photosystem Ii ◽  
Long Range ◽  
Electron Acceptor ◽  
Structural Changes ◽  
Acceptor Site ◽  
Oxygen Evolving Complex ◽  
Long Range Interactions ◽  
Structural Perturbations ◽  
Oxygen Evolving

The Mn4CaO5 cluster site in the oxygen-evolving complex (OEC) of photosystem II (PSII) undergoes structural perturbations, such as those induced by Ca2+/Sr2+ exchanges or Ca/Mn removal. These changes have been known to induce long-range positive shifts (between +30 and +150 mV) in the redox potential of the primary quinone electron acceptor plastoquinone A (QA), which is located 40 Å from the OEC. To further investigate these effects, we reanalyzed the crystal structure of Sr-PSII resolved at 2.1 Å and compared it with the native Ca-PSII resolved at 1.9 Å. Here, we focus on the acceptor site and report the possible long-range interactions between the donor, Mn4Ca(Sr)O5 cluster, and acceptor sites.

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