An RNA alternative to human transferrin: a new tool for targeting human cells.

The transferrin receptor, CD71, is an attractive target for drug development because of its high expression on a number of cancer cell lines and the blood brain barrier. To generate serum-stabilized aptamers that recognize the human transferrin receptor, we have modified the traditional aptamer selection protocol by employing a functional selection step that enriches for RNA molecules which bind the target receptor and are internalized by cells. Selected aptamers were specific for the human receptor, rapidly endocytosed by cells and shared a common core structure.

Increasing the efficacy of bioorthogonal click reactions for bioconjugation: a comparative study.

Raising the bar: the efficacy of bioorthogonal reactions for bioconjugation has been thoroughly evaluated in four different biological settings. Powered by the development of new biocompatible ligands, the copper-catalyzed azide-alkyne cycloaddition has brought about unsurpassed bioconjugation efficiency, and thus it holds great promise as a highly potent and adaptive tool for a broader spectrum of biological applications.

Imaging glycans in zebrafish embryos by metabolic labeling and bioorthogonal click chemistry.

Imaging glycans in vivo has recently been enabled using a bioorthogonal chemical reporter strategy by treating cells or organisms with azide- or alkyne-tagged monosaccharides. The modified monosaccharides, processed by the glycan biosynthetic machinery, are incorporated into cell surface glycoconjugates. The bioorthogonal azide or alkyne tags then allow covalent conjugation with fluorescent probes for visualization, or with affinity probes for enrichment and glycoproteomic analysis.

Biocompatible copper(I) catalysts for in vivo imaging of glycans.

The Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) is the standard method for bioorthogonal conjugation. However, current Cu(I) catalyst formulations are toxic, hindering their use in living systems. Here we report that BTTES, a tris(triazolylmethyl)amine-based ligand for Cu(I), promotes the cycloaddition reaction rapidly in living systems without apparent toxicity.

Chemoenzymatic synthesis of the sialyl Lewis X glycan and its derivatives.

A combination of recombinant FKP and alpha-(1-->3)-fucosyltransferase allows the facile synthesis of the sialyl Lewis X tetrasaccharide glycan and its derivatives in excellent yield. In this system, the universal fucosyl donor, guanidine 5'-diphosphate-beta-L-fucose (GDP-fucose), or its analogues can be generated in situ by cofactor recycling using pyruvate kinase.

Chemoenzymatic synthesis of GDP-L-fucose and the Lewis X glycan derivatives.

Lewis X (Le(x))-containing glycans play important roles in numerous cellular processes. However, the absence of robust, facile, and cost-effective methods for the synthesis of Le(x) and its structurally related analogs has severely hampered the elucidation of the specific functions of these glycan epitopes. Here we demonstrate that chemically defined guanidine 5'-diphosphate-beta-l-fucose (GDP-fucose), the universal fucosyl donor, the Le(x) trisaccharide, and their C-5 substituted derivatives can be synthesized on preparative scales, using a chemoenzymatic approach.