Fluorogenic Photo-Crosslinking of Glycan-Binding Protein Recognition Using a Fluorinated Azido-Coumarin Fucoside.

Glycan recognition by glycan-binding proteins is central to the biology of all living organisms. The efficient capture and characterization of relatively weak non-covalent interactions remains an important challenge in various fields of research. Photoaffinity labeling strategies can create covalent bonds between interacting partners, and photoactive scaffolds such as benzophenone, diazirines and aryl azides have proved widely useful. Since their first introduction, relatively few improvements have been advanced and products of photoaffinity labeling remain difficult to detect. We report a fluorinated azido-coumarin scaffold which enables photolabeling under fast and mild activation, and which can leave a fluorescent tag on crosslinked species. Coupling this scaffold to an α-fucoside, we demonstrate fluorogenic photolabeling of glycan-protein interactions over a wide range of affinities. We expect this strategy to be broadly applicable to other chromophores and we envision that such "fluoro-crosslinkers" could become important tools for the traceable capture of non-covalent binding events.

Aza-Residue Modulation of Cyclic d,l-α-Peptide Nanotube Assembly with Enhanced Anti-Amyloidogenic Activity.

Transient soluble oligomers of amyloid-ß (Aß) are considered among the most toxic species in Alzheimer's disease (AD). Soluble Aß oligomers accumulate early prior to insoluble plaque formation and cognitive impairment. The cyclic d,l-α-peptide CP-2 (1) self-assembles into nanotubes and demonstrates promising anti-amyloidogenic activity likely by a mechanism involving engagement of soluble oligomers. Systematic replacement of the residues in peptide 1 with aza-amino acid counterparts was performed to explore the effects of hydrogen bonding on propensity to mitigate Aß aggregation and toxicity. Certain azapeptides exhibited improved ability to engage, alter the secondary structure, and inhibit aggregation of Aß. Moreover, certain azapeptides disassembled preformed Aß fibrils and protected cells from Aß-mediated toxicity. Substitution of the l-norleucine3 and d-serine6 residues in peptide 1 with aza-norleucine and aza-homoserine provided, respectively, nontoxic [azaNle3]-1 (4) and [azaHse6]-1 (7), that significantly abated symptoms in a transgenic Caenorhabditis elegans AD model by decreasing Aß oligomer levels.