Glycobiology Advance Access originally published online on June 18, 2009
Glycobiology 2009 19(9):1034-1045; doi:10.1093/glycob/cwp084
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The 
-galactomannan Davanat binds galectin-1 at a site different from the conventional galectin carbohydrate binding domain
2 Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota Health Sciences Center, 6-155 Jackson Hall, 321 Church Street, Minneapolis, MN 55455
3 Pro-Pharmaceuticals, Inc, 7 Wells Ave., Newton, MA 02459, USA
1 To whom correspondence should be addressed: Tel: +612-625-9968; Fax: +612-612-2163; e-mail: mayox001{at}umn.edu
Received on May 15, 2009; revised on June 8, 2009; accepted on June 8, 2009
Galectins are a sub-family of lectins, defined by their highly conserved β-sandwich structures and ability to bind to β-galactosides, like Gal β1-4 Glc (lactose). Here, we used 15N-1H HSQC and pulse field gradient (PFG) NMR spectroscopy to demonstrate that galectin-1 (gal-1) binds to the relatively large galactomannan Davanat, whose backbone is composed of β1-4-linked D-mannopyranosyl units to which single D-galactopyranosyl residues are periodically attached via 
1-6 linkage (weight-average MW of 59 kDa). The Davanat binding domain covers a relatively large area on the surface of gal-1 that runs across the dimer interface primarily on that side of the protein opposite to the lactose binding site. Our data show that gal-1 binds Davanat with an apparent equilibrium dissociation constant (Kd) of 10 x 10–6 M, compared to 260 x 10–6 M for lactose, and a stiochiometry of about 3 to 6 gal-1 molecules per Davanat molecule. Mannan also interacts at the same galactomannan binding domain on gal-1, but with at least 10-fold lower avidity, supporting the role of galactose units in Davanat for relatively strong binding to gal-1. We also found that the β-galactoside binding domain remains accessible in the gal-1/Davanat complex, as lactose can still bind with no apparent loss in affinity. In addition, gal-1 binding to Davanat also modifies the supermolecular structure of the galactomannan and appears to reduce its hydrodynamic radius and disrupt inter-glycan interactions thereby reducing glycan-mediated solution viscosity. Overall, our findings contribute to understanding gal-1–carbohydrate interactions and provide insight into gal-1 function with potentially significant biological consequences.
Key words: diffusion / glycan / lectin / NMR spectroscopy / protein Q