Terbium Substitution of the Calcium-Binding Sites in the Oxygen-Evolving Complex of Photosystem II

Hatch, C. D.; Grush, Melissa M.; Bradley, Ryan L.; LoBrutto, Russell; Cramer, Steve; Frasch, Wayne D.

doi:10.1007/978-94-009-0173-5_331

Cited by 4 publications

(9 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Other Mn EXAFS experiments on terbium-(III)-substituted PS II, where Tb 3+ displaced Ca 2+ from its binding site without prior depletion, supported this alternative view. 45 Because Tb 3+ is a competitive inhibitor of Ca 2+ binding, the oxygen-evolving activity was suppressed in these samples but the Mn EXAFS exhibited no change from the substituting lanthanide. Tb 3+ was not needed to fit the ∼3.4 Å distance in the Mn EXAFS spectrum, implying a Ca binding site that is at least 4 Å away from the Mn.…”

Section: Introductionmentioning

confidence: 97%

“…Tb 3+ was not needed to fit the ∼3.4 Å distance in the Mn EXAFS spectrum, implying a Ca binding site that is at least 4 Å away from the Mn. 45 More support came from EPR-based experiments involving Mn 2+ substitution in Ca-depleted (inactive) PS II membranes. These results indicated that the Mn 2+ -occupied Ca binding site was outside the first coordination region of the catalytic cluster 46 (beyond 4 Å).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Strontium EXAFS Reveals the Proximity of Calcium to the Manganese Cluster of Oxygen-Evolving Photosystem II

et al. 1998

View full text Add to dashboard Cite

The oxygen-evolving complex of Photosystem II (PS II) in green plants and algae contains a cluster of four manganese atoms in the active site, which catalyzes the photoinduced oxidation of water to dioxygen. Along with Mn, calcium and chloride ions are necessary cofactors for proper functioning of the complex. A key unresolved question is whether Ca is close to the Mn cluster, within about 3.5 Å. To further test and verify this finding, we substituted strontium for Ca and probed from the Sr point-of-view for any nearby Mn. Sr has been shown to replace Ca and still maintain enzyme activity (about 40% of normal rate). The extended X-ray absorption fine structure (EXAFS) of Sr-PS II probes the local environment around the Sr cofactor to detect any nearby Mn. We focused on the functional Sr by removing nonessential, loosely bound Sr in the protein environment. For comparison, an inactive sample was prepared by treating the intact PS II with hydroxylamine to disrupt the Mn cluster and to produce nonfunctional enzyme. Sr EXAFS results indicate major differences in the phase and amplitude between the functional (intact) and nonfunctional (NHOH-treated) samples. In intact samples, the Fourier transform of the Sr EXAFS shows a peak that is missing in inactive samples. This Fourier peak II is best simulated by two Mn neighbors at a distance of 3.5 Å. Thus, with X-ray absorption studies on Sr-reconstituted PS II, we confirm the proximity of Ca (Sr) cofactor to the Mn cluster and show that the active site is a Mn-Ca heteronuclear cluster.

show abstract

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Strontium EXAFS Reveals the Proximity of Calcium to the Manganese Cluster of Oxygen-Evolving Photosystem II

et al. 1998

View full text Add to dashboard Cite

show abstract

“…The marked decrease in oxidation potential of the S 2 state manganese cluster in K ϩ -, Rb ϩ -, and Cs ϩ -substituted OEC as indicated by the upshifted TL band is very similar to that observed in the Ca 2ϩ -depleted sample membranes prepared by low-pH treatment (Ono and Inoue, 1989a;Ono et al, 1992), in which binding of the 24 kDa protein to Ca 2ϩdepleted OEC causes abnormalities of the manganese cluster, including the alteration of the magnetic properties (Ono and Inoue, 1989a;Ono et al, 1992). Interestingly, the Kedge of the Mn XANES spectrum of low-pH treated membranes downshifts, indicating the modified ligation structural of the manganese cluster such as a broken ligation bond to the cluster (Ono et al, 1991(Ono et al, , 1993Latimer et al, 1995;Cinco et al, 1998), whereas no such spectral change has been identified in Ca 2ϩ -depleted samples devoid of the 24-kDa protein (Hatch et al, 1995;Riggs-Gelasco et al, 1996). EXAFS (Yachandra et al, 1993) and FTIR (Noguchi et al, 1995) studies indicated that Ca 2ϩ is connected with the manganese cluster via a carboxylate bridge, and that this structure is responsible for the conformational change that appears upon S 2 state formation by breaking the coordination to Ca 2ϩ , whereas Ca 2ϩ depletion at low-pH liberates the carboxylate ligand from the manganese cluster (Noguchi et al, 1995).…”

Section: Discussionmentioning

confidence: 99%

“…Trivalent lanthanide cations may occupy the Ca 2ϩ site, but the binding seems to be largely irreversible (Ghanotakis et al, 1985;Bakou et al, 1992;Ono, 2000). Lanthanide-substituted OECs show no S 2 EPR signals (Ghanotakis et al, 1985;Bakou et al, 1992;Hatch et al, 1995), although lanthanide (La 3ϩ or Dy 3ϩ ) substitution induces no significant change in the features of the EXAFS spectra of the manganese cluster (Hatch et al, 1995;Riggs-Gelasco et al, 1996).…”

Section: Introductionmentioning

confidence: 99%

“…Ca 2ϩ is an indispensable metal cofactor required for oxygen evolution that is inhibited by the depletion of one Ca 2ϩ /PSII and is restored by the reconstitution with Ca 2ϩ (Yocum, 1991;Debus, 1992). Extended x-ray absorption fine structure spectroscopy (EXAFS) (Yachandra et al, 1993;Latimer et al, 1995;Cinco et al, 1998) and Fourier transform infrared (FTIR) (Noguchi et al, 1995) studies indicate that Ca 2ϩ is closely associated with the manganese cluster, presumably through a carboxylate bridge to form a multimetal center (Hatch et al, 1995;Riggs-Gelasco et al, 1996). Recently, crystal structure of oxygen-evolving PSII was reported at 3.8 Å resolution, but no electron density could be assigned to the Ca 2ϩ ions (Zouni et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Ca2+ Function in Photosynthetic Oxygen Evolution Studied by Alkali Metal Cations Substitution

Ono

Rompel

Mino

et al. 2001

Biophysical Journal

View full text Add to dashboard Cite

Effects of adding monovalent alkali metal cations to Ca(2+)-depleted photosystem (PS)II membranes on the biochemical and spectroscopic properties of the oxygen-evolving complex were studied. The Ca(2+)-dependent oxygen evolution was competitively inhibited by K(+), Rb(+), and Cs(+), the ionic radii of which are larger than the radius of Ca(2+) but not inhibited significantly by Li(+) and Na(+), the ionic radii of which are smaller than that of Ca(2+). Ca(2+)-depleted membranes without metal cation supplementation showed normal S(2) multiline electron paramagnetic resonance (EPR) signal and an S(2)Q(A)(-) thermoluminescence (TL) band with a normal peak temperature after illumination under conditions for single turnover of PSII. Membranes supplemented with Li(+) or Na(+) showed properties similar to those of the Ca(2+)-depleted membranes, except for a small difference in the TL peak temperatures. The peak temperature of the TL band of membranes supplemented with K(+), Rb(+), or Cs(+) was elevated to approximately 38 degrees C which coincided with that of Y(D)(+)Q(A)(-) TL band, and no S(2) EPR signals were detected. The K(+)-induced high-temperature TL band and the S(2)Q(A)(-) TL band were interconvertible by the addition of K(+) or Ca(2+) in the dark. Both the Ca(2+)-depleted and the K(+)-substituted membranes showed the narrow EPR signal corresponding to the S(2)Y(Z)(+) state at g = 2 by illuminating the membranes under multiple turnover conditions. These results indicate that the ionic radii of the cations occupying Ca(2+)-binding site crucially affect the properties of the manganese cluster.

show abstract

Calcium EXAFS Establishes the Mn-Ca Cluster in the Oxygen-Evolving Complex of Photosystem II

et al. 2002

View full text Add to dashboard Cite

The proximity of Ca to the Mn cluster of the photosynthetic water-oxidation complex is demonstrated by X-ray absorption spectroscopy. We have collected EXAFS data at the Ca Kedge using active PS II membrane samples that contain approximately 2 Ca per 4 Mn. These samples are much less perturbed than previously investigated Sr-substituted samples, which were prepared subsequent to Ca depletion. The new Ca EXAFS clearly shows backscattering from Mn at 3.4 Å, a distance that agrees with that surmised from previously recorded Mn EXAFS. This result is also consistent with earlier related experiments at the Sr K-edge, using samples that contained functional Sr, that show Mn is ~ 3.5 Å distant from Sr. The totality of the evidence clearly advances the notion that the catalytic center of oxygen evolution is a Mn-Ca heteronuclear cluster. 4Calcium is essential as a cofactor for photosynthetic oxygen evolution in green plants and algae. Together with another cofactor, chloride, calcium is involved in a four-manganese cluster to catalyze the light-driven oxidation of water into dioxygen, protons and electrons for carbon fixation (1-4). The water-splitting reaction occurs within the oxygen-evolving complex (OEC 1 ) of photosystem II (PS II), located in the thylakoid membranes of green plants, cyanobacteria and algae. It is crucial to study the Ca cofactor as recent mechanisms of oxygen evolution (5-9) have proposed roles for Ca (and Cl) that require it to be located near the Mn cluster. Studies on photoactivation and assembly of the Mn cluster also implicate a requirement for nearby Ca in the light-induced assembly of the water-oxidizing complex (10-12).While the Mn cluster has been extensively researched, mainly by X-ray absorption spectroscopy (XAS) (13-16) and electron paramagnetic resonance (EPR) techniques (17), the calcium cofactor has been comparatively less studied (1,18,19). This is explained by the lack of spectroscopic handles for Ca compared to Mn. Previous work on the structure of the binding site of the Ca cofactor has mainly consisted of studies involving Ca depletion (20-23) or substituting other metals (24) including strontium, manganese or terbium for the cofactor (25-28). FTIR spectroscopy suggests a carboxylate bridge between Mn and Ca in PS II (29), but a later study disputes this finding (30). Structural information about the binding site of the Ca cofactor has been obtained recently through extended X-ray absorption fine structure (EXAFS) experiments on strontium-substituted PS II membranes (31-33) and through 87 Sr ESEEM (electron spin echo envelope modulation) spectroscopy (R. D. Britt, personal communication, 2002).Strontium is the only metal ion that replaces calcium and still maintains oxygen-evolving activity (up to 40% at saturating light levels) (34). Earlier efforts using Mn EXAFS on Srreactivated PS II (31) implicated a 3.5 Å distance between the Mn cluster and Sr. More recently, Sr EXAFS on similar samples confirms this finding of a 3.5 Å distance between Sr and Mn in the OEC (32)...

show abstract

Terbium Substitution of the Calcium-Binding Sites in the Oxygen-Evolving Complex of Photosystem II

Cited by 4 publications

References 9 publications

Strontium EXAFS Reveals the Proximity of Calcium to the Manganese Cluster of Oxygen-Evolving Photosystem II

Strontium EXAFS Reveals the Proximity of Calcium to the Manganese Cluster of Oxygen-Evolving Photosystem II

Ca2+ Function in Photosynthetic Oxygen Evolution Studied by Alkali Metal Cations Substitution

Calcium EXAFS Establishes the Mn-Ca Cluster in the Oxygen-Evolving Complex of Photosystem II

Contact Info

Product

Resources

About