O-GlcNAc Transferase Recognizes Protein Substrates Using an Asparagine Ladder in the Tetratricopeptide Repeat (TPR) Superhelix.

The essential mammalian enzyme O-GlcNAc Transferase (OGT) is uniquely responsible for transferring N-acetylglucosamine to over a thousand nuclear and cytoplasmic proteins, yet there is no known consensus sequence and it remains unclear how OGT recognizes its substrates. To address this question, we developed a protein microarray assay that chemoenzymatically labels de novo sites of glycosylation with biotin, allowing us to simultaneously assess OGT activity across >6000 human proteins. With this assay we examined the contribution to substrate selection of a conserved asparagine ladder within the lumen of OGT's superhelical tetratricopeptide repeat (TPR) domain.

Improved Carbohydrate Recognition in Water with an Electrostatically Enhanced β-Peptide Bundle.

The selective recruitment of oligosaccharides, or even simple sugars, in water solvent is an unsolved molecular recognition problem. Structure-guided, electrostatic redesign led to a significant increase in the affinity of a β-peptide "borono-bundle" for simple sugars in neutral aqueous solution. The affinity for fructose (663 M(-1)) in water should allow its recruitment to the bundle surface for selective catalysis, and future work will focus in this direction.

Positive allostery in metal ion binding by a cooperatively folded β-peptide bundle.

Metal ion binding is exploited by proteins in nature to catalyze reactions, bind molecules, and favor discrete structures, but it has not been demonstrated in β-peptides or their assemblies. Here we report the design, synthesis, and characterization of a β-peptide bundle that uniquely binds two Cd(II) ions in a distinct bicoordinate array. The two Cd(II) ions bind with positive allosteric cooperativity and increase the thermodynamic stability of the bundle by more than 50 °C.

A β-boronopeptide bundle of known structure as a vehicle for polyol recognition.

Despite significant progress in the design of receptors and sensors for simple polyols and monosaccharides, few synthetic receptors discriminate among multiple saccharide units simultaneously, especially under physiological conditions. Described here is the three-dimensional structure of a supramolecular complex-a β-peptide bundle-designed for the potential to interact simultaneously with as many as eight discrete monosaccharide units. The preliminary evaluation of this construct as a vehicle for polyol binding is also presented.