Self-assembled monolayers of globotriaosylceramide (Gb3) mimics: surface-specific affinity with shiga toxins

Self-assembled monolayers (SAMs) of Gb3 mimics having different lengths of alkyl chains were prepared on gold surfaces, and their interactions with galactose-specific lectin (RCA(120)) and Shiga toxins (Stxs) were investigated by a quartz crystal microbalance (QCM) in aqueous solutions. Their interaction with RCA(120) was enhanced owing to the "cluster effect," regardless of the alkyl chain length of the SAMs. The interaction with Stxs was dependent on the alkyl chain length of Gb3 mimics. Stx-1 and Stx-2 showed a stronger affinity to the Gb3C2 SAM with ethyl disulfide and to the Gb3C10 with decyl disulfide, respectively. Gb3 glycoconjugate polymer with no alkyl spacer inhibited the adsorption of Stx-1 to Gb3C10 SAM but did not inhibit the adsorption of Stx-2 to Gb3C10 SAM. The results suggest that the alkyl chain of the glycolipid takes part in the binding to Stx-2 but not to Stx-1, which is also supported by the computer simulation of Stx-1 with a Gb3 model substance.