Substrate Binding Drives Active-Site Closing of Human Blood Group B Galactosyltransferase as Revealed by Hot-Spot Labeling and NMR Spectroscopy Experiments

Glycan structures and their interactions with proteins. A NMR view

Carbohydrate molecules are essential actors in key biological events, being involved as recognition points for cell-cell and cell-matrix interactions related to health and disease. Despite outstanding advances in cryoEM, X-ray crystallography and NMR still remain the most employed techniques to unravel their conformational features and to describe the structural details of their interactions with biomolecular receptors. Given the intrinsic flexibility of saccharides, NMR methods are of paramount importance to deduce the extent of motion around their glycosidic linkages and to explore their receptor-bound conformations. We herein present our particular view on the latest advances in NMR methodologies that are permitting to magnify their applications for deducing glycan conformation and dynamics and understanding the recognition events in which there are involved.

Novel NMR Avenues to Explore the Conformation and Interactions of Glycans

This perspective article is focused on the presentation of the latest advances in NMR methods and applications that are behind the exciting achievements in the understanding of glycan receptors in molecular recognition events. Different NMR-based methodologies are discussed along with their applications to scrutinize the conformation and dynamics of glycans as well as their interactions with protein receptors.

Insights into Allosteric Control of Human Blood Group A and B Glycosyltransferases from Dynamic NMR

Human blood group A and B glycosyltransferases (GTA, GTB) are retaining glycosyltransferases, requiring a catalytic mechanism that conserves the anomeric configuration of the hexopyranose moiety of the donor substrate (UDP-GalNAc, UDP-Gal). Previous studies have shown that GTA and GTB cycle through structurally distinct states during catalysis. Here, we link binding and release of substrates, substrate-analogs, and products to transitions between open, semi-closed, and closed states of the enzymes. Methyl TROSY based titration experiments in combination with zz-exchange experiments uncover dramatic changes of binding kinetics associated with allosteric interactions between donor-type and acceptor-type ligands. Taken together, this highlights how allosteric control of on- and off-rates correlates with conformational changes, driving catalysis to completion.

Complete assignment of Ala, Ile, Leu, Met and Val methyl groups of human blood group A and B glycosyltransferases using lanthanide-induced pseudocontact shifts and methyl-methyl NOESY

Human blood group A and B glycosyltransferases (GTA, GTB) are highly homologous glycosyltransferases. A number of high-resolution crystal structures is available showing that these enzymes convert from an open conformation into a catalytically active closed conformation upon substrate binding. However, the mechanism of glycosyltransfer is still under debate, and the precise nature as well as the time scales of conformational transitions are unknown. NMR offers a variety of experiments to shine more light on these unresolved questions. Therefore, in a first step we have assigned all methyl resonance signals in MILVA labeled samples of GTA and GTB, still a challenging task for 70 kDa homodimeric proteins. Assignments were obtained from methyl-methyl NOESY experiments, and from measurements of lanthanide-induced pseudocontact shifts (PCS) using high resolution crystal structures as templates. PCSs and chemical shift perturbations, induced by substrate analogue binding, suggest that the fully closed state is not adopted in the presence of lanthanide ions.