4 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 Ć
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 ādoming modeā 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 āsaddling modeā 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 āthe local steric protein environmentā
rather than the redox potential value in PSII
Photosystem II Does Not Possess a Simple Excitation Energy Funnel: Time-Resolved Fluorescence Spectroscopy Meets Theory
The experimentally
obtained time-resolved fluorescence spectra
of photosystem II (PS II) core complexes, purified from a thermophilic
cyanobacterium Thermosynechococcus vulcanus, at 5ā180 K are compared with simulations. Dynamic localization
effects of excitons are treated implicitly by introducing exciton
domains of strongly coupled pigments. Exciton relaxations within a
domain and exciton transfers between domains are treated on the basis
of Redfield theory and generalized FoĢrster theory, respectively.
The excitonic couplings between the pigments are calculated by a quantum
chemical/electrostatic method (Poisson-TrEsp). Starting with previously
published values, a refined set of site energies of the pigments is
obtained through optimization cycles of the fits of stationary optical
spectra of PS II. Satisfactorily agreement between the experimental
and simulated spectra is obtained for the absorption spectrum including
its temperature dependence and the linear dichroism spectrum of PS
II core complexes (PS II-CC). Furthermore, the refined site energies
well reproduce the temperature dependence of the time-resolved fluorescence
spectrum of PS II-CC, which is characterized by the emergence of a
695 nm fluorescence peak upon cooling down to 77 K and the decrease
of its relative intensity upon further cooling below 77 K. The blue
shift of the fluorescence band upon cooling below 77 K is explained
by the existence of two red-shifted chlorophyll pools emitting at
around 685 and 695 nm. The former pool is assigned to Chl45 or Chl43
in CP43 (Chl numbering according to the nomenclature of Loll et al. <i>Nature</i> <b>2005</b>, <i>438</i>, 1040) while
the latter is assigned to Chl29 in CP47. The 695 nm emitting chlorophyll
is suggested to attract excitations from the peripheral light-harvesting
complexes and might also be involved in photoprotection
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 Ć
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 Ć
from the nitrogen
NĪ“ of the imidazole ring of D2-His336. By MALDI-TOF/MS upon
tryptic digestion, it is shown that ā¼20ā30% 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
Oxygen-Evolving Porous Glass Plates Containing the Photosynthetic Photosystem II PigmentāProtein Complex
The
development of artificial photosynthesis has focused on the
efficient coupling of reaction at photoanode and cathode, wherein
the production of hydrogen (or energy carriers) is coupled to the
electrons derived from water-splitting reactions. The natural photosystem
II (PSII) complex splits water efficiently using light energy. The
PSII complex is a large pigmentāprotein complex (20 nm in diameter)
containing a manganese cluster. A new photoanodic device was constructed
incorporating stable PSII purified from a cyanobacterium Thermosynechococcus vulcanus through immobilization
within 20 or 50 nm nanopores contained in porous glass plates (PGPs).
PSII in the nanopores retained its native structure and high photoinduced
water splitting activity. The photocatalytic rate (turnover frequency)
of PSII in PGP was enhanced 11-fold compared to that in solution,
yielding a rate of 50ā300 mol e<sup>ā</sup>/(mol PSIIĀ·s)
with 2,6-dichloroindophenol (DCIP) as an electron acceptor. The PGP
system realized high local concentrations of PSII and DCIP to enhance
the collisional reactions in nanotubes with low disturbance of light
penetration. The system allows direct visualization/determination
of the reaction inside the nanotubes, which contributes to optimize
the local reaction condition. The PSII/PGP device will substantively
contribute to the construction of artificial photosynthesis using
water as the ultimate electron source