Glycobiology Advance Access published online on May 4, 2005
Glycobiology, doi:10.1093/glycob/cwi069
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1 Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India
* To whom correspondence should be addressed. Synthetic cluster glycosides have often been used to unravel mechanisms of carbohydrate-protein interactions. While synthetic cluster glycosides are constituted on to scaffolds in order to achieve high avidities in lectin binding, there have been no known attempts to modulate the orientations of the sugar clusters with the aid of a functional scaffold on to which the sugar units are linked. Herein, we describe synthesis, physical and lectin binding studies of a series of
Received March 10, 2005
Revised April 23, 2005
Accepted April 25, 2005
Article
Photoswitchable Cluster Glycosides as Tools to Probe Carbohydrate-Protein Interactions: Synthesis and Lectin Binding Studies of Azobenzene Containing Multivalent Sugar Ligands
2 Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
Avadhesha Surolia, E-mail: surolia{at}mbu.iisc.ernet.in
Narayanaswamy Jayaraman, E-mail: jayaraman{at}orgchem.iisc.ernet.in
Abstract 
-D-mannopyranoside and 
-D-galactopyranosyl-(1
4)--D-glucopyranoside glycoclusters that are attached to a photoswitchable azobenzenoid core. These glycoclusters were synthesized by amidation of amine-tethered glycopyranosides with azobenzene carbonyl chlorides. From kinetic studies, the cis-forms of the azobenzene-glycopyranoside derivative were found to be more stable in aqueous solutions than in organic solvents. Molecular modeling studies were performed in order to estimate the relative geometries of the photoswitchable glycoclusters in the trans- and cis- isomeric forms. Isothermal titration calorimetry (ITC) was employed to assess the binding of these glycoclusters to lectins peanut agglutinin and concanavalin A. While binding affinities were enhanced several orders higher as the valency of the sugar was increased, a biphasic binding profile in ITC plots was observed during few glycoclusters-lectin binding processes. The biphasic binding profile indicates a ‘co-operativity’ in the binding process. An important outcome of the present study is that in addition to inherent clustering of the sugar units as a molecular feature, an induced clustering emanates as a result of the isomerization of the trans-form of the azobenzene scaffold to the cis-isomeric form.
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