Surface plasmon resonance imaging for real-time, label-free analysis of protein interactions with carbohydrate microarrays.

Plant lectin recognition of glycans was evaluated by SPR imaging using a model array of N-biotinylated aminoethyl glycosides of beta-D-glucose (negative control), alpha-D: -mannose (conA-responsive), beta-D-galactose (RCA(120)-responsive) and N-acetyl-beta-D-: glucosamine (WGA-responsive) printed onto neutravidin-coated gold chips. Selective recognition of the cognate ligand was observed when RCA(120) was passed over the array surface. Limited or no binding was observed for the non-cognate ligands. SPR imaging of an array of 40 sialylated and unsialylated glycans established the binding preference of hSiglec7 for alpha2-8-linked disialic acid structures over alpha2-6-sialyl-LacNAcs, which in turn were recognized and bound with greater affinity than alpha2-3-sialyl-LacNAcs. Affinity binding data could be obtained with as little as 10-20 microg of lectin per experiment. The SPR imaging technique was also able to establish selective binding to the preferred glycan ligand when analyzing crude culture supernatant containing 10-20 microg of recombinant hSiglec7-Fc. Our results show that SPR imaging provides results that are in agreement with those obtained from fluorescence based carbohydrate arrays but with the added advantage of label-free analysis.