2 research outputs found
Deformation of Chlorin Rings in the Photosystem II Crystal Structure
The crystal structure of Photosystem II (PSII) analyzed
at a resolution
of 1.9 Å revealed deformations of chlorin rings in the chlorophylls
for the first time. We investigated the degrees of chlorin ring deformation
and factors that contributed to them in the PSII crystal structure,
using a normal-coordinate structural decomposition procedure. The
out-of-plane distortion of the P<sub>D1</sub> chlorin ring can be
described predominantly by a large “doming mode” arising
from the axial ligand, D1-His198, as well as the chlorophyll side
chains and PSII protein environment. In contrast, the deformation
of P<sub>D2</sub> was caused by a “saddling mode” arising
from the D2-Trp191 ring and the doming mode arising from D2-His197.
Large ruffling modes, which were reported to lower the redox potential
in heme proteins, were observed in P<sub>D1</sub> and Chl<sub>D1</sub>, but not in P<sub>D2</sub> and Chl<sub>D2</sub>. Furthermore, as
P<sub>D1</sub> possessed the largest doming mode among the reaction
center chlorophylls, the corresponding bacteriochlorophyll P<sub>L</sub> possessed the largest doming mode in bacterial photosynthetic reaction
centers. However, the majority of the redox potential shift in the
protein environment was determined by the electrostatic environment.
The difference in the chlorin ring deformation appears to directly
refer to the difference in “the local steric protein environment”
rather than the redox potential value in PSII
Evidence for an Unprecedented Histidine Hydroxyl Modification on D2-His336 in Photosystem II of <i>Thermosynechoccocus vulcanus</i> and <i>Thermosynechoccocus elongatus</i>
The electron density map of the 3D
crystal of Photosystem II from Thermosynechococcus
vulcanus with a 1.9 Å resolution
(PDB: 3ARC)
exhibits, in the two monomers in the asymmetric unit cell, an, until
now, unidentified and uninterpreted strong difference in electron
density centered at a distance of around 1.5 Å from the nitrogen
Nδ of the imidazole ring of D2-His336. By MALDI-TOF/MS upon
tryptic digestion, it is shown that ∼20–30% of the fragments
containing the D2-His336 residue of Photosystem II from both Thermosynechococcus vulcanus and Thermosynechococcus
elongatus bear an extra mass of +16 Da. Such an extra
mass likely corresponds to an unprecedented post-translational or
chemical hydroxyl modification of histidine