Huub J. M. de Groot

Backbone and Side-Chain 13C and 15N Signal Assignments of the α-Spectrin SH3 Domain by Magic Angle Spinning Solid-State NMR at 17.6 Tesla

The backbone and side‐chain 13C and 15N signals of a solid 62‐residue (u‐13C,15N)‐labelled protein containing the α‐spectrin SH3 domain were assigned by two‐dimensional (2D) magic angle spinning (MAS) 15N–13C and 13C–13C dipolar correlation spectroscopy at 17.6 T. The side‐chain signal sets of the individual amino acids were identified by 2D 13C–13C proton‐driven spin diffusion and dipolar recoupling experiments. Correlations to the respective backbone nitrogen signals were established by 2D NCACX (CX=any carbon atom) experiments, which contain a proton–nitrogen and a nitrogen–carbon cross‐polarisation step followed by a carbon–carbon homonuclear transfer unit. Interresidue correlations leading to sequence‐specific assignments were obtained from 2D NCOCX experiments. The assignment is nearly complete for the SH3 domain residues 7–61, while the signals of the N‐ and C‐terminal residues 1–6 and 62, respectively, outside the domain boundaries are not detected in our MAS spectra. The resolution observed in these spectra raises expectations that receptor‐bound protein ligands and slightly larger proteins (up to 20 kDa) can be readily assigned in the near future by using three‐dimensional versions of the applied or analogous techniques.

Alternating syn-anti bacteriochlorophylls form concentric helical nanotubes in chlorosomes

Chlorosomes are the largest and most efficient light-harvesting antennae found in nature, and they are constructed from hundreds of thousands of self-assembled bacteriochlorophyll (BChl) c, d, or e pigments. Because they form very large and compositionally heterogeneous organelles, they had been the only photosynthetic antenna system for which no detailed structural information was available. In our approach, the structure of a member of the chlorosome class was determined and compared with the wild type (WT) to resolve how the biological light-harvesting function of the chlorosome is established. By constructing a triple mutant, the heterogeneous BChl c pigment composition of chlorosomes of the green sulfur bacteria Chlorobaculum tepidum was simplified to nearly homogeneous BChl d. Computational integration of two different bioimaging techniques, solid-state NMR and cryoEM, revealed an undescribed syn-anti stacking mode and showed how ligated BChl c and d self-assemble into coaxial cylinders to form tubular-shaped elements. A close packing of BChls via π–π stacking and helical H-bonding networks present in both the mutant and in the WT forms the basis for ultrafast, long-distance transmission of excitation energy. The structural framework is robust and can accommodate extensive chemical heterogeneity in the BChl side chains for adaptive optimization of the light-harvesting functionality in low-light environments. In addition, syn-anti BChl stacks form sheets that allow for strong exciton overlap in two dimensions enabling triplet exciton formation for efficient photoprotection.

Surface‐Immobilized Single‐Site Iridium Complexes for Electrocatalytic Water Splitting

however, the design andimplementation of a stable and efficient molecular wateroxidation system that operates at high catalytic turnovernumber (TON) and frequency (TOF) for extended periods ofcontrolled-potential electrolysis (CPE), with moderate over-potential and high current density, are challenging.

(1)H and (13)C MAS NMR evidence for pronounced ligand-protein interactions involving the ionone ring of the retinylidene chromophore in rhodopsin.

Rhodopsin is a member of the superfamily of G-protein-coupled receptors. This seven α-helix transmembrane protein is the visual pigment of the vertebrate rod photoreceptor cells that mediate dim light vision. In the active binding site of this protein the ligand or chromophore, 11-cis-retinal, is covalently bound via a protonated Schiff base to lysine residue 296. Here we present the complete 1H and 13C assignments of the 11-cis-retinylidene chromophore in its ligand-binding site determined with ultra high field magic angle spinning NMR. Native bovine opsin was regenerated with 99% enriched uniformly 13C-labeled 11-cis-retinal. From the labeled pigment, 13C carbon chemical shifts could be obtained by using two-dimensional radio frequency-driven dipolar recoupling in a solid-state magic angle spinning homonuclear correlation experiment. The 1H chemical shifts were assigned by two-dimensional heteronuclear (1H-13C) dipolar correlation spectroscopy with phase-modulated Lee–Goldburg homonuclear 1H decoupling applied during the t1 period. The data indicate nonbonding interactions between the protons of the methyl groups of the retinylidene ionone ring and the protein. These nonbonding interactions are attributed to nearby aromatic acid residues Phe-208, Phe-212, and Trp-265 that are in close contact with, respectively, H-16/H-17 and H-18. Furthermore, binding of the chromophore involves a chiral selection of the ring conformation, resulting in equatorial and axial positions for CH3-16 and CH3-17.

Longitudinal assessment of Alzheimer's β‐amyloid plaque development in transgenic mice monitored by in vivo magnetic resonance microimaging

To assess the development of β‐amyloid (Aβ) plaques in the brain with age in the transgenic mouse model of Alzheimers disease (AD) pathology by in vivo magnetic resonance microimaging (μMRI).

Zinc chlorins for artificial light-harvesting self-assemble into antiparallel stacks forming a microcrystalline solid-state material

We introduce a concept to solve the structure of a microcrystalline material in the solid-state at natural abundance without access to distance constraints, using magic angle spinning (MAS) NMR spectroscopy in conjunction with X-ray powder diffraction and DFT calculations. The method is applied to a novel class of materials that form (semi)conductive 1D wires for supramolecular electronics and artificial light-harvesting. The zinc chlorins 3-devinyl-31-hydroxymethyl-132-demethoxycarbonylpheophorbide a (3′,5′-bis-dodecyloxy)benzyl ester zinc complex 1 and 3-devinyl-31-methoxymethyl-132-demethoxycarbonylpheophorbide a (3′,5′-bis-dodecyloxy)benzyl ester zinc complex 2, self-assemble into extended excitonically coupled chromophore stacks. 1H-13C heteronuclear dipolar correlation MAS NMR experiments provided the 1H resonance assignment of the chlorin rings that allowed accurate probing of ring currents related to the stacking of macrocycles. DFT ring-current shift calculations revealed that both chlorins self-assemble in antiparallel π-stacks in planar layers in the solid-state. Concomitantly, X-ray powder diffraction measurements for chlorin 2 at 80 °C revealed a 3D lattice for the mesoscale packing that matches molecular mechanics optimized aggregate models. For chlorin 2 the stacks alternate with a periodicity of 0.68 nm and a 3D unit cell with an approximate volume of 6.28 nm3 containing 4 molecules, which is consistent with space group P21221.

Artificial Photosynthesis for Solar Fuels – an Evolving Research Field within AMPEA, a Joint Programme of the European Energy Research Alliance

Abstract On the path to an energy transition away from fossil fuels to sustainable sources, the European Union is for the moment keeping pace with the objectives of the Strategic Energy Technology-Plan. For this trend to continue after 2020, scientific breakthroughs must be achieved. One main objective is to produce solar fuels from solar energy and water in direct processes to accomplish the efficient storage of solar energy in a chemical form. This is a grand scientific challenge. One important approach to achieve this goal is Artificial Photosynthesis. The European Energy Research Alliance has launched the Joint Programme “Advanced Materials & Processes for Energy Applications” (AMPEA) to foster the role of basic science in Future Emerging Technologies. European researchers in artificial photosynthesis recently met at an AMPEA organized workshop to define common research strategies and milestones for the future. Through this work artificial photosynthesis became the first energy research sub-field to be organised into what is designated “an Application” within AMPEA. The ambition is to drive and accelerate solar fuels research into a powerful European field – in a shorter time and with a broader scope than possible for individual or national initiatives. Within AMPEA the Application Artificial Photosynthesis is inclusive and intended to bring together all European scientists in relevant fields. The goal is to set up a thorough and systematic programme of directed research, which by 2020 will have advanced to a point where commercially viable artificial photosynthetic devices will be under development in partnership with industry.

MAGIC ANGLE SPINNING NMR STUDIES ON THE METARHODOPSIN II INTERMEDIATE OF BOVINE RHODOPSIN: EVIDENCE FOR AN UNPROTONATED SCHIFF BASE

Abstract— Magic angle spinning (MAS)W‐NMR spectra of the metarhodopsin II intermediate h been obtained using bovine rhodopsin regenerated with retinal 13C‐labeled at the C‐13 and C positions to investigate the protonation state of the retinal Schiff base linkage. The 13C‐labe rhodopsin was reconstituted into 1,2‐dipalmitoleoylphosphatidylcholine bilayers to increase the amo of meta II trapped at low temperature. Both the 13C‐15 (159.2 ppm) and 13C‐13 (144.0 ppm) isotropic chemical shifts are characteristic of an unprotonated Schiff base, while the “C‐15 shift is significantly different from that of retinal (191 ppm) or a tetrahedral carbinolamine group (70–90 ppm) previously proposed as an intermediate in the hydrolysis of the Schiff base at the meta II stage. This rules the possibility that meta II non‐covalently binds retinal or is a carbinolamine intermediate and provi convincing evidence that Schiff base deprotonation occurs in the meta I‐meta II transition, an ev that is likely to be important in triggering the activation of transducin.

15N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem II

In natural photosynthesis, the two photosystems that operate in series to drive electron transport from water to carbon dioxide are quite similar in structure and function, but operate at widely different potentials. In both systems photochemistry begins by photo-oxidation of a chlorophyll a, but that in photosystem II (PS2) has a 0.7 eV higher midpoint potential than that in photosystem I (PS1), so their electronic structures must be very different. Using reaction centers from 15N-labeled spinach, these electronic structures are compared by their photochemically induced dynamic nuclear polarization (photo-CIDNP) in magic-angle spinning (MAS) NMR measurements. The results show that the electron spin distribution in PS1, apart from its known delocalization over 2 chlorophyll molecules, reveals no marked disturbance, whereas the pattern of electron spin density distribution in PS2 is inverted in the oxidized radical state. A model for the donor of PS2 is presented explaining the inversion of electron spin density based on a tilt of the axial histidine toward pyrrole ring IV causing π-π overlap of both aromatic systems.

Magnetic resonance microscopy of mouse embryos in utero

Magnetic resonance microscopy (MRM) was used to study mouse embryonic development in utero. MRM is a non‐invasive imaging technique to study normal and abnormal embryonic development. To overcome image blurring as a result of embryonic movement, fast imaging sequences were used (less than 1 min scanning time). Clear morphologic proton images were obtained by diffusion spin echo and by rapid acquisition with relaxation enhancement (RARE), revealing living mouse embryos with great anatomical detail. In addition, functional information about embryonic blood flow could be obtained, in the absence of a contrast agent. This was achieved by combining two imaging sequences, RARE and very fast gradient echo. We expect that MRM will soon become a feasible method to study longitudinally both normal and abnormal (transgenic) mouse development. Anat Rec 260:373–377, 2000.