Glycans of cellular glycoconjugates serve as biochemical signals for a multitude of (patho)physiological processes via binding to their receptors (e.g. lectins). In the case of human adhesion/growth-regulatory galectin-1 (Gal-1), small angle neutron scattering and fluorescence correlation spectroscopy have revealed a significant decrease of its gyration radius and increase of its diffusion coefficient upon binding lactose, posing the pertinent question on the nature and region(s) involved in the underlying structural alterations. Requiring neither a neutron source nor labeling, diffusion measurements by 1H NMR spectroscopy are shown here to be sufficiently sensitive to detect this ligand-induced change. In order to figure out which region(s) of Gal-1 is (are) affected at the level of peptides, we first explored the use of H/D exchange mass spectrometry (HDX MS). Hereby, we found a reduction in proton exchange kinetics beyond the lactose-binding site. The measurement of fast HN/H2O exchange by phase-modulated NMR clean chemical exchange (CLEANEX) NMR on 15N-labeled Gal-1 then increased the spatial resolution to the level of individual amino acids. The mapped regions with increased protection from HN/H2O (D2O) exchange that include the reduction of solvent exposure around the interface can underlie the protein's compaction. These structural changes have potential to modulate this galectin's role in lattice formation on the cell surface and its interaction(s) with protein(s) at the F-face.
Bibliographical noteFunding Information:
This work was supported by the Department of Industry, Tourism and Trade of the Government of the Autonomous Community of the Basque Country (Elkartek BG2019 ; to T.D.) and the Severo Ochoa Excellence Accreditation from MCIU ( SEV-2016-0644 ; to T.D.).
© 2021 Elsevier B.V. and Société Française de Biochimie et Biologie Moléculaire (SFBBM)
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