Detection of an Electron Paramagnetic Resonance Signal in the S₀ State of the Manganese Complex of Photosystem II from Synechococcus elongatus

Abstract

The Mn(4)-cluster of photosystem II (PSII) from Synechococcus elongatus was studied by electron paramagnetic resonance (EPR) spectroscopy after a series of saturating laser flashes given in the presence of either methanol or ethanol. Results were compared to those obtained in similar experiments done on PSII isolated from plants. The flash-dependent changes in amplitude of the EPR multiline signals were virtually identical in all samples. In agreement with earlier work [Messinger, J., Nugent, J. H. A., and Evans, M. C. W. (1997) Biochemistry 36, 11055-11060; Ahrling, K. A., Peterson, S., and Styring, S. (1997) Biochemistry 36, 13148-13152], detection of an EPR multiline signal from the S(0) state in PSII from plants was only possible with methanol present. In PSII from S. elongatus, it is shown that the S(0) state exhibits an EPR multiline signal in the absence of methanol (however, ethanol was present as a solvent for the artificial electron acceptor). The hyperfine lines are better resolved when methanol is present. The S(0) multiline signals detected in plant PSII and in S. elongatus were similar but not identical. Unlike the situation seen in plant PSII, the S(2) state in S. elongatus is not affected by the addition of methanol in that (i) the S(2) multiline EPR signal is not modified by methanol and (ii) the spin state of the S(2) state is affected by infrared light when methanol is present. It is also shown that the magnetic relaxation properties of an oxidized low-spin heme, attributed to cytochrome c(550), vary with the S states. This heme then is in the magnetic environment of the Mn(4) cluster.

Focusing the view on nature's water-splitting catalyst

“…However, with high sample concentrations we did observe a broad, featureless signal around gZ2 for the S 0 state in samples containing no methanol (Messinger et al 1997). Similarly, Thermosynechococcus elongatus preps display an S 0 EPR signal in absence of methanol (Boussac et al 1999 Mn-ENDOR spectra we derive four effective hyperfine interaction tensors, A i,iso . These form the basis for the further analysis, in which we derive for different spin-coupling models possible exchange couplings between the individual Mn ions.…”

X-ray absorption spectroscopy to analyze nuclear geometry and electronic structure of biological metal centers?potential and questions examined with special focus on the tetra-nuclear manganese complex of oxygenic photosynthesis

“…10). This means that an unbiased inspection of the inflectionpoint shift for the S 0 →S 1 transition is suggestive of a twoelectron oxidation, a presumption that is clearly unreasonable in the light of EPR results [66,73,74,75,76,77]. For the S 2 →S 3 transition, it has been reported that the edge-shift is clearly smaller than the S 1 →S 2 shift [70,71] whereas others found it to be of comparable magnitude [31,34,35].…”

Structure of the Mn4–Ca cluster as derived from X-ray diffraction

“…Nevertheless cyt c-550 interacts directly with D1 and provides two hydrogen bonds with the C-terminal helix of D1 (V-Lys160NfÁÁÁD1-Glu329Oe and V-Tyr163OÁÁÁD1-Arg323NH). Spectroscopic studies revealed an influence of cyt c-550 on the electron transfer reaction at the donor side of PSII, on the Ca 2+ requirement for water oxidation (Li et al 2004) and on the EPR signals of the Mn 4 -Ca cluster (Boussac et al 1999;Lakshmi et al 2002). Furthermore it was observed in plant PSII preparations that the absence or presence of the two small membrane-extrinsic proteins (PsbP and PsbQ in higher plants) influences the magnetic properties of the Mn 4 -Ca cluster ).…”