Abstract
Human galectin-3 (Gal-3) is a β-galactoside-binding lectin. This multitasking protein preferentially interacts with N-acetyllactosamine moieties on glycoconjugates. Specific hydroxyl groups (4-OH, 6-OH of galactose, and 3-OH of glucose/N-acetylglucosamine) of lactose/LacNAc are essential for their binding to Gal-3. Through hemagglutination inhibition, microcalorimetry, and spectroscopy, we have shown that despite being a lectin, Gal-3 possesses the characteristics of a glycosaminoglycan (GAG)-binding protein (GAGBP). Gal-3 interacts with sulfated GAGs [heparin, chondroitin sulfate-A (CSA), -B (CSB), and -C (CSC)] and chondroitin sulfate proteoglycans (CSPGs). Heparin, CSA, and CSC showed micromolar affinity for Gal-3, while the affinity of CSPGs for Gal-3 was much higher (nanomolar). Interestingly, CSA, CSC, and a bovine CSPG, not heparin and CSB, were multivalent ligands for Gal-3, and they formed reversible noncovalent cross-linked complexes with the lectin. Binding of sulfated GAGs to Gal-3 was completely inhibited when Gal-3 was preincubated with β-lactose. Cross-linking of Gal-3 by CSA, CSC, and the bovine CSPG was also reversed by β-lactose. These findings strongly suggest that GAGs primarily occupy the lactose/LacNAc binding site of Gal-3. Identification of Gal-3 as a GAGBP should help to reveal new functions of Gal-3 mediated by GAGs and proteoglycans. The GAG- and CSPG-binding properties of Gal-3 make the lectin a potential competitor/collaborator of other GAGBPs such as growth factors, cytokines, morphogens, and extracellular matrix proteins.
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Acknowledgments
This work was supported by National Science Foundation Grant 1608537 (to T.K.D.). A part of this work was supported by a startup fund (to P.B.) and by the Research Excellence Fund (to T.K.D.) provided by Michigan Technological University.
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Edwards, J.L., Kadav, P.D., Bandyopadhyay, P., Dam, T.K. (2022). Revealing the Identity of Human Galectin-3 as a Glycosaminoglycan-Binding Protein. In: Stowell, S.R., Arthur, C.M., Cummings, R.D. (eds) Galectins. Methods in Molecular Biology, vol 2442. Humana, New York, NY. https://doi.org/10.1007/978-1-0716-2055-7_8
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DOI: https://doi.org/10.1007/978-1-0716-2055-7_8
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