Ligation of D1-His332 and D1-Asp170 to the Manganese Cluster of Photosystem II from Synechocystis Assessed by Multifrequency Pulse EPR Spectroscopy

Abstract

Multifrequency electron-spin echo envelope modulation (ESEEM) spectroscopy is used to ascertain the nature of the bonding interactions of various active site amino acids with the Mn ions that compose the oxygen-evolving cluster (OEC) in photosystem II (PSII) from the cyanobacterium Synechocystis sp. PCC 6803 poised in the S2 state. Spectra of natural isotopic abundance PSII (14N-PSII), uniformly 15N-labeled PSII (15N-PSII), as well as 15N-PSII containing 14N-histidine (14N-His/15N-PSII) are compared. These complementary data sets allow for a precise determination of the spin Hamiltonian parameters of the postulated histidine nitrogen interaction with the Mn ions of the OEC. These results are compared to those from a similar study on PSII isolated from spinach. Upon mutation of His332 of the D1 polypeptide to a glutamate residue, all isotopically sensitive spectral features vanish. Additional Ka- and Q-band ESEEM experiments on the D1-D170H site-directed mutant give no indication of new 14N-based interactions.

Ammonia binding to the oxygen-evolving complex of photosystem II identifies the solvent-exchangeable oxygen bridge (μ-oxo) of the manganese tetramer

“…The parameters used (Table 1, Fig. S2, and Table S2) are similar to those reported earlier by Stich et al (31) for PSII purified from Synechocystis sp. 6803.…”

“…Instead, the observed ESEEM modulation is dominated by a 14 N hyperfine coupling assigned to the D1-His332 ligand of Mn D1 (31). At Q-band the histidine 14 N signal is at or near the cancellation condition and as such displays a maximal ESEEM response (30,31). As a consequence of the D1-His332 14 N coupling matching the cancellation condition, the signal of the bound ammonia in comparison is suppressed at Q-band and no direct information on its binding site can be obtained in this way.…”

“…2C and 2D). Instead, the observed ESEEM modulation is dominated by a 14 N hyperfine coupling assigned to the D1-His332 ligand of Mn D1 (31). At Q-band the histidine 14 N signal is at or near the cancellation condition and as such displays a maximal ESEEM response (30,31).…”

“…6803. The relatively large magnitude of the D1-His332 14 N coupling suggests that it is ligated to the only Mn III ion in the S 2 state, i.e., to the Mn ion that carries the largest spin density/spin projection (11,30,31). As the D1-His332 signal does not change upon the addition of ammonia, the oxidation state and ligand field of the Mn D1 ion cannot change.…”

Proton Matrix ENDOR Studies on Ca2+-depleted and Sr2+-substituted Manganese Cluster in Photosystem II

“…EPR spectroscopy has been used to characterize the manganese cluster (23)(24)(25)(26) extensively, and a typical, S 2 state multiline signal centered at g ϭ 2 has been well characterized. The multiline signal showed 19 -21 peaks in a range over ϳ180 mT width, and its properties have been studied by several advanced EPR techniques such as 55 Mn-ENDOR (27), ESEEM (28,29), and pulsed ELDOR (30). The ENDOR results indicated that the S 2 state is composed of one Mn(III) and three Mn(IV), where the Mn(III) ion is assigned to the Mn1 ion in the crystal structure ( Fig.…”