Systematic analysis of barrier-forming FG hydrogels from Xenopus nuclear pore complexes.

Nuclear pore complexes (NPCs) control the traffic between cell nucleus and cytoplasm. While facilitating translocation of nuclear transport receptors (NTRs) and NTR·cargo complexes, they suppress passive passage of macromolecules 30 kDa. Previously, we reconstituted the NPC barrier as hydrogels comprising S. cerevisiae FG domains. We now studied FG domains from 10 Xenopus nucleoporins and found that all of them form hydrogels. Related domains with low FG motif density also substantially contribute to the NPC's hydrogel mass. We characterized all these hydrogels and observed the strictest sieving effect for the Nup98-derived hydrogel. It fully blocks entry of GFP-sized inert objects, permits facilitated entry of the small NTR NTF2, but arrests importin ß-type NTRs at its surface. O-GlcNAc modification of the Nup98 FG domain prevented this arrest and allowed also large NTR·cargo complexes to enter. Solid-state NMR spectroscopy revealed that the O-GlcNAc-modified Nup98 gel lacks amyloid-like ß-structures that dominate the rigid regions in the S. cerevisiae Nsp1 FG hydrogel. This suggests that FG hydrogels can assemble through different structural principles and yet acquire the same NPC-like permeability.

Π-π stacking increases the stability and loading capacity of thermosensitive polymeric micelles for chemotherapeutic drugs.

Thermosensitive amphiphilic block copolymers self-assemble into micelles above their lower critical solution temperature in water, however, the micelles generally display mediocre physical stability. To stabilize such micelles and increase their loading capacity for chemotherapeutic drugs, block copolymers with novel aromatic monomers were synthesized by free radical polymerization of N-(2-benzoyloxypropyl methacrylamide (HPMAm-Bz) or the corresponding naphthoyl analogue (HPMAm-Nt), with N-(2-hydroxypropyl) methacrylamide monolactate, using a polyethylene glycol based macroinitiator. The critical micelle temperatures and critical micelle concentrations decreased with increasing the HPMAm-Bz/Nt content. The micelles of 30-50 nm were prepared by heating the polymer aqueous solutions from 0 to 50 °C and were colloidally stable for at least 48 h at pH 7.4 and 37 °C. Paclitaxel and docetaxel encapsulation was performed by mixing drug solutions in ethanol with polymer aqueous solutions and heating from 0 to 50 °C. The micelles had a drug loading capacity up to 34 wt % for docetaxel, which is among the highest loadings reported for polymeric micelles, with loaded micelle sizes ranging from 60 to 80 nm. The micelles without aromatic groups almost completely released loaded paclitaxel in 10 days, whereas the HPMAm-Bz/Nt containing micelles released 50% of the paclitaxel at the same time, which showed a better retention for the drug of the latter micelles. (1)H solid-state NMR spectroscopy data are compatible with π-π stacking between aromatic groups. The empty micelles demonstrated good cytocompatibility, and paclitaxel-loaded micelles showed high cytotoxicity to tumor cells. In conclusion, the π-π stacking effect introduced by aromatic groups increases the stability and loading capacity of polymeric micelles.

Rapid prediction of multi-dimensional NMR data sets.

We present a computational environment for Fast Analysis of multidimensional NMR DAta Sets (FANDAS) that allows assembling multidimensional data sets from a variety of input parameters and facilitates comparing and modifying such "in silico" data sets during the various stages of the NMR data analysis. The input parameters can vary from (partial) NMR assignments directly obtained from experiments to values retrieved from in silico prediction programs. The resulting predicted data sets enable a rapid evaluation of sample labeling in light of spectral resolution and structural content, using standard NMR software such as Sparky. In addition, direct comparison to experimental data sets can be used to validate NMR assignments, distinguish different molecular components, refine structural models or other parameters derived from NMR data. The method is demonstrated in the context of solid-state NMR data obtained for the cyclic nucleotide binding domain of a bacterial cyclic nucleotide-gated channel and on membrane-embedded sensory rhodopsin II. FANDAS is freely available as web portal under WeNMR ( http://www.wenmr.eu/services/FANDAS ).

Shape Control of Colloidal Cu2-x S Polyhedral Nanocrystals by Tuning the Nucleation Rates.

Synthesis protocols for colloidal nanocrystals (NCs) with narrow size and shape distributions are of particular interest for the successful implementation of these nanocrystals into devices. Moreover, the preparation of NCs with well-defined crystal phases is of key importance. In this work, we show that Sn(IV)-thiolate complexes formed in situ strongly influence the nucleation and growth rates of colloidal Cu2-x S polyhedral NCs, thereby dictating their final size, shape, and crystal structure. This allowed us to successfully synthesize hexagonal bifrustums and hexagonal bipyramid NCs with low-chalcocite crystal structure, and hexagonal nanoplatelets with various thicknesses and aspect ratios with the djurleite crystal structure, by solely varying the concentration of Sn(IV)-additives (namely, SnBr4) in the reaction medium. Solution and solid-state 119Sn NMR measurements show that SnBr4 is converted in situ to Sn(IV)-thiolate complexes, which increase the Cu2-x S nucleation barrier without affecting the precursor conversion rates. This influences both the nucleation and growth rates in a concentration-dependent fashion and leads to a better separation between nucleation and growth. Our approach of tuning the nucleation and growth rates with in situ-generated Sn-thiolate complexes might have a more general impact due to the availability of various metal-thiolate complexes, possibly resulting in polyhedral NCs of a wide variety of metal-sulfide compositions.

Solid-state NMR [13C,15N] resonance assignments of the nucleotide-binding domain of a bacterial cyclic nucleotide-gated channel.

Channels regulated by cyclic nucleotides are key signalling proteins in several biological pathways. The regulatory aspect is conferred by a C-terminal cyclic nucleotide-binding domain (CNBD). We report resonance assignments of the CNBD of a bacterial mlCNG channel obtained using 2D and 3D solid-state NMR under Magic-angle Spinning conditions. A secondary chemical shift analysis of the 141 residue protein suggests a three-dimensional fold seen in earlier X-ray and solution-state NMR work and points to spectroscopic polymorphism for a selected set of resonances.