Abstract
The medically important drug target galectin-3 binds galactose-containing moieties on glycoproteins through an intricate pattern of hydrogen bonds to a largely polar surface-exposed binding site. All successful inhibitors of galectin-3 to date have been based on mono- or disaccharide cores closely resembling natural ligands. A detailed understanding of the H-bonding networks in these natural ligands will provide an improved foundation for the design of novel inhibitors. Neutron crystallography is an ideal technique to reveal the geometry of hydrogen bonds because the positions of hydrogen atoms are directly detected rather than being inferred from the positions of heavier atoms as in X-ray crystallography. We present three neutron crystal structures of the C-terminal carbohydrate recognition domain of galectin-3: the ligand-free form and the complexes with the natural substrate lactose and with glycerol, which mimics important interactions made by lactose. The neutron crystal structures reveal unambiguously the exquisite fine-tuning of the hydrogen bonding pattern in the binding site to the natural disaccharide ligand. The ligand-free structure shows that most of these hydrogen bonds are preserved even when the polar groups of the ligand are replaced by water molecules. The protonation states of all histidine residues in the protein are also revealed and correlate well with NMR observations. The structures give a solid starting point for molecular dynamics simulations and computational estimates of ligand binding affinity that will inform future drug design.
Highlights
The specific binding of carbohydrate binding proteins to glycoproteins or glycolipids directs a large variety of cellular processes, such as adhesion to other cells and trafficking of intracellular components
We present three neutron crystal structures of the C-terminal carbohydrate recognition domain of galectin-3: the ligand-free form and the complexes with the natural substrate lactose and with glycerol, which mimics important interactions made by lactose
The three neutron crystal structures of galectin-3C presented here identify for the first time experimentally the positions of key hydrogen atoms in ligand complexes and in the apo protein, thereby highlighting the exquisite fine-tuning of Hbonding interactions in the carbohydrate binding site to exploit all available interaction possibilities in the disaccharide core and providing experimental support for geometry that could only be inferred until now
Summary
The specific binding of carbohydrate binding proteins (lectins) to glycoproteins or glycolipids directs a large variety of cellular processes, such as adhesion to other cells and trafficking of intracellular components. There is great interest in understanding the detailed molecular mechanisms governing the binding specificity between lectins and their cognate carbohydrate chains. This binding generally involves many hydrogen bonds, whose directionality can be difficult to characterize, as well as many indirect and dynamic interactions via water molecules. The carbohydrate-recognition domain (CRD) is C-terminal, while the N-terminal domain is involved in oligomerization, probably through formation of a coiled-coil structure, a characteristic that is unique among the galectin family proteins.[1]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
