By definition, adhesion/growth-regulatory galectins are known for their ability to bind β-galactosides such as Gal(1 → 4)Glc (lactose). Indications for affinity of human galectin-1 to α-linked digalactosides pose questions on the interaction profile with such bound ligands and selection of the galactose moiety for CH-π stacking. These issues are resolved by a combination of 15N- 1H heteronuclear single quantum coherence (HSQC) chemical shift and saturation transfer difference nuclear magnetic resonance (STD NMR) epitope mappings with docking analysis, using the (1 → 3/4)-linked digalactosides and also Gal(1 → 6)Glc (melibiose) as test compounds. The experimental part revealed interaction with the canonical lectin site, and this preferentially via the non-reducing-end galactose moiety. Low-energy conformers appear to be selected without notable distortion, as shown by molecular dynamics simulations. With the (1 → 4) disaccharide, however, the typical CH-π interaction is significantly diminished, yet binding appears to be partially compensated for by hydrogen bonding. Overall, these findings reveal that the type of-linkage in digalactosides has an impact on maintaining CH-π interactions and the pattern of hydrogen bonding, explaining preference for the (1 → 3) linkage. Thus, this lectin is able to accommodate both α-and β-linked galactosides at the same site, with major contacts to the non-reducing-end sugar unit.
Bibliographical noteFunding Information:
This work was sponsored by research grants from the National Cancer Institute (NIH grant # CA096090) to KHM, the Ministery of Science and Innovation of Spain (CTQ2009-08536) to JJ-B and the EC Seventh Framework Program (FP7/2007-2013) under grant agreement no. 260600 (“GlycoHIT”) to JJ-B and H-JG.
The authors wish to thank the Minnesota Supercomputing Institute (University of Minnesota) for providing computer resources. NMR instrumentation was provided with funds from the NSF (BIR-961477), the University of Minnesota Medical School and the Minnesota Medical Foundation.
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