Abstract
Galectins are multi-purpose effectors acting via interactions with distinct counterreceptors based on protein-glycan/protein recognition. These processes are emerging to involve several regions on the protein so that the availability of a detailed structural characterization of a full-length galectin is essential. We report here the first crystallographic information on the N-terminal extension of the carbohydrate recognition domain of rat galectin-5, which is precisely described as an N-tailed proto-type-like galectin. In the ligand-free protein, the three amino-acid stretch from Ser2 to Ser5 is revealed to form an extra β-strand (F0), and the residues from Thr6 to Asn12 are part of a loop protruding from strands S1 and F0. In the ligand-bound structure, amino acids Ser2–Tyr10 switch position and are aligned to the edge of the β-sandwich. Interestingly, the signal profile in our glycan array screening shows the sugar-binding site to preferentially accommodate the histo-blood-group B (type 2) tetrasaccharide and N-acetyllactosamine-based di- and oligomers. The crystal structures revealed the characteristically preformed structural organization around the central Trp77 of the CRD with involvement of the sequence signature’s amino acids in binding. Ligand binding was also characterized calorimetrically. The presented data shows that the N-terminal extension can adopt an ordered structure and shapes the hypothesis that a ligand-induced shift in the equilibrium between flexible and ordered conformers potentially acts as a molecular switch, enabling new contacts in this region.
Highlights
Introduction iationsStorage of biological information involves more than nucleic acids and proteins
By using an array platform with 609 compounds, the spacered histo-blood-group B tetrasaccharide, LacNAc-based dimers and the xenoantigen with α1,3-linked galactose added to a LacNAc core were found to be frontrunners in terms of signal intensity, together with several bacterial polysaccharides (Figure 2; for a complete listing of compounds and signal intensities, please see Supplementary Material, Table S1). rat galectin-5 (rGal-5), in contrast to galectin-related protein (GRP), which has lost the ability to bind β-galactosides [19], presents a profile with typical selectivity among this class of glycans
To report the contact pattern between rGal-5 and the selected carbohydrate ligands, we carried out systematic screening to find conditions for crystallization
Summary
Introduction iationsStorage of biological information involves more than nucleic acids and proteins. The ubiquity of occurrence, the enormous diversity already at the level of oligomers and the fine-tuned spatiotemporal regulation of the appearance of distinct structures are solid arguments for a fundamental functional meaning of the glycan part of cellular glycoconjugates [1,2,3,4,5,6]. By molecular complementarity of oligosaccharides with a contact region in the carbohydrate recognition domains (CRDs) of sugar-binding proteins (lectins), glycan-encoded messages are ‘read’ and ‘translated’ into cellular effects [6,7,8]. Toward this end, triggering specific bioeffects, the selection of the binding partner(s), appears to matter.
Sign-in/Register to view highlights & summary 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.
