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The pathway and its possible role for water oxidation in photosystem II (PSII) is elucidated by calculating the pKa for the residues along the proposed proton exit pathway by solving the linearized Poisson-Boltzmann equation for the whole PSII complex, taking into account the atomic coordinates of all amino acid residues and bound cofactors. The pKa of these residues are dramatically affected when the atomic coordinates of PsbO are removed, indicating a significant role of PsbO in tuning the pKa of those residues in the proton pathway.

Author(s): Bernhard Loll [1, 3, 4]; Jan Kern [2, 4]; Wolfram Saenger (corresponding author) [1]; Athina Zouni (corresponding author) [2]; Jacek Biesiadka [1] Oxygenic photosynthesis in plants, algae and cyanobacteria [...]

The overexpression of Escherichia coli and the characterization of the gene product by biochemical and spectroscopic methods are described. recPsbO was titrated in the presence of Ca(super 2+), followed by UV-circular dichroism spectropolarimetry (CD) and Fourier transform infrared spectroscopy in order to elucidate probable Ca(super 2+) binding site(s), but no significant changes in the secondary structure could be observed.

The oxygen-evolving photosystem II core complexes (PSIIcc) from the thermophilic cyanobacterium Thermosynechococcus elongatus (PSIIccTe) and the higher plant Spinacia oleracea (PSIIccSo) are isolated from the thylakoid membrane by solubilization with n-dodecyl-beta-D-maltoside, purified and characterized by gel permeation chromatography (GPC), dynamic light scattering (DLS), and analytical centrifugation (AUC). The results are discussed from a crystallization point of view.

Programmed cell death in prokaryotes is frequently found as postsegregational killing. It relies on antitoxin/toxin systems that secure stable inheritance of low and medium copy number plasmids during cell division and kill cells that have lost the plasmid. The broad-host-range, low-copy-number plasmid pSM19035 from Streptococcus pyogenes carries the genes encoding the antitoxin/ toxin system [epsilon]/[zeta] and antibiotic resistance proteins, among others. The crystal structure of the biologically nontoxic [[epsilon].sub.2[[zeta].sub.2] protein complex at a 1.95-[Angstrom] resolution and site-directed mutagenesis showed that free [zeta] acts as phosphotransferase by using ATP/GTP. In [[epsilon].sub.2][[zeta]. sub.2], the toxin [zeta] is inactivated because the N-terminal helix of the antitoxin [epsilon] blocks the ATP/GTP-binding site. To our knowledge, this is the first prokaryotic postsegregational killing system that has been entirely structurally characterized. programmed cell death | [epsilon] protein | [epsilon] protein | toxin inactivation | phosphotransferase

Author(s): Patrick Jordan [1]; Petra Fromme [2]; Horst Tobias Witt [2]; Olaf Klukas [1]; Wolfram Saenger [1]; Norbert Krauß [1, 3] All higher organisms on earth receive their energy directly [...]

Photon and fluorescence correlation spectroscopic studies yield the same apparent hydrodynamic radii measurement for the hexameric RepA DNA-helicase dimer and its complex with the single-stranded DNA. Data reveal that the RepA DNA-helicase binds to single-stranded DNA optimally under acidic conditions leading to a structural change in the former.

Author(s): Athina Zouni [1]; Horst-Tobias Witt [1]; Jan Kern [1]; Petra Fromme [1]; Norbert Krauss [2]; Wolfram Saenger (corresponding author) [2]; Peter Orth [2] Oxygenic photosynthesis is the principal energy [...]

Research has been conducted on the homohexameric DNA helicase RepA's ATPase activity. The steady-state parameters of this activity and the binding of the fluorescent analogue to RepA have been investigated.

Research is presented describing the used of dynamic light scattering to observe the cluster formation of electrolyte solutions in water.

Research was conducted to examine the interaction kinetics of tetramethylrhodamine (TMR) transferrin with human transferrin receptor (hTfR) using fluorescence correlation spectroscopy. The dissociation constant for the equilibrium binding of TMR-labeled ferri-transferrin to hTfR in detergent free solution was determined to be 7+/-3 microns. An enthalpy change of -44.4 kJ/mol was achieved which shows that the reaction is mainly enthalpy driven.

Research was conducted to examine the structure of octakis(2,3,6-tri-O-methyl)-gamma-cyclodextrin (TRIMEG) crystalized from saturated aqueous solution at 18 degrees C. Ab initio real/reciprocal space recycling technique was used to determine the structures of the four TRIMEG molecules having a similar elliptical shape with pseudo-2-fold rotational symmetry. Results suggest that other methylated CDs are hydrated in a similar way at low temperature which may explain their high solubility.

Simultaneous static and dynamic light scattering was used to examine the formation of clusters in nucleating hen egg white lysozyme-NaCl solutions. Angular dependent measurements of the average cluster diffusion coefficient and the total scattered intensity indicated pronounced structure peaks at the initial nucleation stages. These peaks suggest an ordering similar to that observed in highly concentrated colloidal suspensions.

The role of Mg2+ ions in (MgTc)(super +) binding and in the induction of the homodimeric tetracycline repressor (TetR) has been studied. TetR resistance is conferred through homodimers that bind with the alpha-helix-turn-alpha-helix motifs to two nearly identical palindromic operators. The homodimers block the expression of the genes tetA and tetR which encode for the membrane-bound Tc efflux protein TetA and with TetR itself.

Advances in the study of the structures of the doughnut-shaped cyclic oligosaccharides called cyclodextrins are reviewed. Findings on the structural characteristics of cyclodextrin molecules include the view that the glucose is a rigid unit, the torsion angle index and the steadiness of the glucosyl torsion angles phi and psi. The crystal structures are either channels or cages. Cycloamyloses were also observed to have may O-H...O and C-H...O hydrogen bonds.

A study using time-resolved small-angle static light scattering and light microscopy was conducted on the liquid-liquid coexistence region of aqueous lysozyme-NaCl solutions. The findings indicate that the undercooling in the liquid phase and the surface energy between liquid and solid phases contribute in lowering the kinetic barriers to crystallization. Moreover, the results confirm the importance of detailed observations of protein nucleation events on wide spatiotemporal scales and over the phase transition plane.

A study was conducted on aggregation and nucleation events induced by simple electrolytes such as NaCl. The results indicate the existence of a delicate balance between the conditions that optimize charge screening and those promoting gel formation. Moreover, a nonmonotonic behavior of dimensionalities and exponents is seen when the latter are plotted as a function of lysozyme or electrolyte concentration.

The properties of nucleating lysozyme solutions at a variety of lysozyme ad NaC1 concentrations at pH 4.2, have been investigated, using isothermal conduction microcalorimetry and small-angle static light scattering. Significant heat-power peaks are seen at finite times, dependent on levels of supersaturation. The calorimetric results agree with the nucleation behaviour determined in small-angle scattering experiments.

Two different methods of synthesizing dendrimers with poly(p-phenylene) (PPP)-derived cores are presented. The first starts from the functionalized PPPs as polymeric cores whose functional groups are employed to anchor dendrons. The second utilizes benzene derived monomers which already carry dendrons and which are then transferred into the corresponding PPP by some cleanly proceeding step-growth polymerization.

An examination of the initial crystallization phase of native and dimethylated beta-cyclodextrins using small-angle static light scattering found that a single-step mechanism is responsible for the crystal formation of native beta-cyclodextrin. A more complex mechanism for the crystal formation of the heptakis(2,6)-di-O-methyl-beta-CD was noted. It was also found to involve a fast and a slow process. Crystallization exponents suggest that crystallization proceeds with the formation of spherical clusters which unite further to form rod-shaped macrocrystals.

The subcell formed from the two central D-glucopyranoses of beta-D-cellotetraose hemihydrate represents the crystal structure of cellulose II. A model of cellulose II based on this subcell is confirmed by the spectroscopic data. The O6 groups of cellulose II are in the gt orientations. Intramolecular O3***O5',O6' and intermolecular O2a***O6a and O2a***O2b interactions are observed in models of cellulose II. In beta-D-cellotetraose, the orientations of all C6-O6 bonds are gauche, trans.

Light-scattering studies on the thermally induced crystallization transition of beta-cyclodextrin in the range between 343.2 and 283.2 K with the critical temperature 307.3 K indicate that the observed transition resembles the transition from subcritical to postcritical nucleation. The initial cluster size at 343.2 K is 125 plus or minus 21 nm, and the final cluster size at 283.2 K is 400 plus or minus 72 nm. Static light-scattering measurements indicate that subcritical nuclei are more compact than postcritical nuclei.

The infrared spectra of wild type ribonuclease T1 and three mutants reveal the existence of basic differences in the hydrogen bonding pattern in the beta strands. These mutants influence the activity of the enzymes. The peptide backbone bonds along with side-chain marker bonds are used as monitors of conformation to determine the structural variations. The mutations reduce the temperature of thermal transition.

The water molecules in hydrophobic cyclodextrin cavities that are unable to align in the preferred tetrahedral or planar trigonal C-H...O hydrogen bond coordination and that have a propensity to satisfy 'free' acceptor potentials by C-H...Ow interactions with the cavity wall, whose H...Ow distances are marginally lower than 2.4 angstroms, were studied to generalize these qualities to water molecules in different settings. Neutron diffraction data was resorted to because they offer H placements experimentally established to plus or minus 0.01 angstroms and better. The CH donors may be involved in the coordination of water molecules in the same fashion and with the same operationality as OH and NH.

Photosystem I (PS I) of the cyanobacterium Synechococcus was mapped out in three dimensions at the six angstrom level using X-ray analysis. PS I contains the reaction centers for photosynthesis, the process by which the higher plants and cyanobacteria derive chemical energy from light energy. PS I is made up of iron-sulphur clusters, chlorophyll a and two large subunits of nine alpha-helices associated through a two-fold rotation axis.

Geometrical properties of C-H...O hydrogen bonds in carbohydrate crystal structures were analyzed on the basis of 30 neutron diffraction studies. A total of 21% of the H atoms are engaged in C-H...O interactions with H...O separations of less than 2.5 angstrom and only 7% of the H atoms have no contact to O shorter than 3.0 angstrom. It was shown that this type of hydrogen bonds is an integral part of intra- and intermolecular interactions of this substance class.

A study was conducted on the participation of histidine-40 in ribonuclease T1 catalysis. Three-dimensional crytsal structures of the His40Lys mutant were analyzed. The results revealed that His40Lys mutation does not induce major changes in the structure of RNase T1. Further observations also showed that Lys40 side chains existing in the mutant structures inhabit almost the same space.

A study of the covalent O-D bond lengthening in hydroxyl groups showed a gradual reduction in long-distance interactions of hydrogen bonding. Two beta-cyclodextrin complexes were studied based on the low-temperature, high-resolution neutron diffraction data. It was also found that O-D bond length is influenced by three-center hydrogen-bonding and the 'cooperative' effect.