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Glycobiology Advance Access published online on June 18, 2009
Glycobiology, doi:10.1093/glycob/cwp084
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

The {alpha}-galactomannan Davanat binds galectin-1 at a site different from the conventional galectin carbohydrate binding domain

Michelle C. Miller1, Anatole Klyosov2 and Kevin H. Mayo1,*

1 Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota Health Sciences Center, 6-155 Jackson Hall, 321 Church Street, Minneapolis, MN 55455
2 Pro-Pharmaceuticals, Inc, 7 Wells Ave., Newton, MA 02459

* Address correspondence to K H Mayo at the Dept. of Biochemistry, email: mayox001{at}umn.edu

Received on May 15, 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-β(1->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 {alpha}(1->6)-D-galacto-β(1->4)-D-mannan Davanat (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: NMR spectroscopy / diffusion / protein / lectin / glycan / galactose


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