N-Glycosylation starts in the endoplasmic reticulum (ER) where a 14-sugar glycan composed of three glucoses, nine mannoses, and two N-acetylglucosamines (Glc(3)Man(9)GlcNAc(2)) is transferred to nascent proteins. The glucoses are sequentially trimmed by ER-resident glucosidases. The Glc(3)Man(9)GlcNAc(2) moiety is the substrate for oligosaccharyltransferase; the Glc(1)Man(9)GlcNAc(2) and Man(9)GlcNAc(2) intermediates are signals for glycoprotein folding and quality control in the calnexin/calreticulin cycle. Here, we report a novel membrane-anchored ER protein that is highly conserved in animals and that recognizes the Glc(2)-N-glycan. Structure determination by nuclear magnetic resonance showed that its luminal part is a carbohydrate binding domain that recognizes glucose oligomers. Carbohydrate microarray analyses revealed a uniquely selective binding to a Glc(2)-N-glycan probe. The localization, structure, and binding specificity of this protein, which we have named malectin, open the way to studies of its role in the genesis, processing and secretion of N-glycosylated proteins.

Quantum dot core-shell structures are essential to superior optical properties. However, Cd-based quantum dots grown from wurtzite CdSe cores still suffer from irreproducibility due to gel formation during the core synthesis. Moreover, stateof-the-art shelling procedures often remain time consuming. We report here (1) a new procedure of the wurtzite CdSe quantum dot synthesis which eliminates the phosphonic anhydride contamination and (2) the improvement and generalization of the flash synthesis for the growth of highly luminescent multi-shell heterostructures. The high versatility of the flash procedure enables the epitaxial shelling of wurtzite CdSe by CdS, ZnS and even CdZnS alloys, resulting in a significant enhancement of their photoluminescence efficiency. Thanks to a modification of the CdSe/CdS dot-in-rods synthesis to prevent tip-to-tip connections, the flash procedure could also be extended to these anisotropic structures for the growth of multi-shell nanorods as well. The high-quality optical and stability properties of these multi-shell flash heterostructures are of great interest for applications ranging from lighting and displays to long term cell labeling.

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a b s t r a c tWhen it comes to failing or injured tissues and organs, patients often end up on waiting lists for tissue or even organ transplantation negatively affecting the patient's quality of life. The multidisciplinary research field of tissue engineering may offer more innovative ways to replace or ideally regenerate failing tissues and organs. A widely used material in this research field is gelatin because of its biocompatibility and interesting hydrogel forming properties. However, at body temperature gelatin's mechanical properties are greatly reduced due to the dissolution of collagen-like triple helices. With the aim to obtain materials that retain their mechanical properties at body temperature, we propose to combine sodium alginate and methacrylamide-modified gelatin (Gel-MOD) in the form of a graft copolymer to obtain a material that closely resembles the extracellular matrix. The obtained materials can be cross-linked via three distinct pathways including cation mediated, temperature mediated or via covalent bond formation after UV irradiation in the presence of a photo-initiator. The current contribution covers the synthesis of the above mentioned alginate-graft-gelatin copolymers and the characterization of the resulting hydrogels. The materials developed are highly hydrophilic, showing high gel fractions and satisfactory mechanical properties. Moreover the attained storage moduli were tunable by divalent cation addition (72-275% increase at 21°C, 42-405% increase at 40°C). One formulation was found to outperform Gel-MOD in terms of mechanical properties at 40°C, thus indicating the proposed strategy can be used to improve the mechanical properties of gelatin-based hydrogels. Moreover, in vitro biocompatibility assays indicated that cell adhesion and proliferation improves with increasing gelatin content. The present paper illustrates that the developed triple cross-linkable materials are suitable cell carriers, promising to be applied for biomedical purposes.

Trypanosoma brucei, the causative agent of African sleeping sickness, encodes three cysteine homologues (Px I-III) of classical selenocysteine-containing glutathione peroxidases. The enzymes obtain their reducing equivalents from the unique trypanothione (bis(glutathionyl)spermidine)/tryparedoxin system. During catalysis, these tryparedoxin peroxidases cycle between an oxidized form with an intramolecular disulfide bond between Cys 47 and Cys 95 and the reduced peroxidase with both residues in the thiol state. Here we report on the three-dimensional structures of oxidized T. brucei Px III at 1.4 Å resolution obtained by x-ray crystallography and of both the oxidized and the reduced protein determined by NMR spectroscopy. Px III is a monomeric protein unlike the homologous poplar thioredoxin peroxidase (TxP). Trypanosomes and Leishmania, the causative agents of several tropical diseases, have a unique thiol redox metabolism that is based on trypanothione (N 1 ,N 8 -bis(glutathionyl)spermidine) and the flavoenzyme trypanothione reductase (for reviews, see Refs. 1 and 2). The parasites lack catalases and selenocysteine-containing glutathione peroxidases. 2-Cys-peroxiredoxins and cysteine-containing glutathione peroxidasetype enzymes are responsible for hydroperoxide reduction acting both as tryparedoxin peroxidases (for a recent review, see Ref.3). With NADPH as primary electron source, the reducing equivalents flow via trypanothione and tryparedoxin (Tpx), 2 a distant relative of the thioredoxin protein family, onto the peroxidases which then reduce the hydroperoxide substrates (Scheme 1). In Trypanosoma brucei, the causative agent of African sleeping sickness, both the cytosolic 2-Cys peroxiredoxin and the glutathione peroxidase-type enzymes proved to be essential (4, 5).Classical glutathione peroxidases (GPXs) are selenoproteins. Five distinct enzymes have been characterized in mammals, cytosolic GPX1, gastro-intestinal GPX2, plasma GPX3, phospholipid hydroperoxide peroxidase GPX4, and in humans, GPX6, which is restricted to the olfactory system (6). The high specificity of GPX1 for glutathione as reducing substrate gave the protein family its name (7). In the epididymis of rodents and monkeys, a GPX5 is expressed that contains an active site cysteine instead of the selenocysteine. Recently the structure of human GPX7, also a cysteine homologue, has been solved (PDB code 2P31). Expression of this gene is dramatically down-regulated in breast cancer cells (8). In general, cysteine-containing glutathione peroxidase-type enzymes are widespread in nature, and most of the enzymes, few of which are biochemically characterized, function as thioredoxin peroxidases (for reviews, see Refs. 9 and 10).The selenoenzymes contain a catalytic triad. The selenoate of the peroxidatic selenocysteine is supposed to be stabilized by hydrogen bonds with a Gln and a Trp residue (11, 12). Site-directed mutagenesis (13) and computational studies (14, 15) supported the crucial role of the Gln and Trp residue for catalysis. Both residues ...

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