Surface Plasmon Resonance Imaging Studies of Protein-Carbohydrate Interactions

Carbohydrate arrays fabricated on gold films were used to study carbohydrate-protein interactions with surface plasmon resonance (SPR) imaging. An immobilization scheme consisting of the formation of a surface disulfide bond was used to attach thiol-modified carbohydrates onto gold films and to fabricate carbohydrate arrays. The carbohydrate attachment steps were characterized using polarization modulation Fourier transform infrared reflection absorption spectroscopy; and poly(dimethylsiloxane) microchannels were used to immobilize probe compounds at discrete locations on a gold film. The binding of the carbohydrate-binding proteins concanavalin A (ConA) and jacalin to arrays composed of the monosaccharides mannose and galactose was monitored with SPR imaging. SPR imaging measurements were employed to accomplish the following: (i) construct adsorption isotherms for the interactions of ConA and jacalin to the carbohydrate surfaces, (ii) monitor protein binding to surfaces presenting different compositions of the immobilized carbohydrates, and (iii) measure the solution equilibrium dissociation constants for ConA and jacalin toward mannose and galactose, respectively. Adsorption coefficients (KADS) of 2.2 ± 0.8 × 107 M-1 and 5.6 ± 1.7 × 106 M-1 were obtained for jacalin adsorbing to a galactose surface and ConA adsorbing to a mannose surface, respectively. The solution equilibrium dissociation (KD) constant for the interaction of jacalin and galactose was found to be 16 ± 5 μM, and for ConA and mannose was found to be 200 ± 50 μM.