Dehydration effect on the recognition of amphiphiles with many pendent mannose residues by concanavalin A

Amphiphiles which carried many pendent mannose residues as side chains were prepared by telomerization of 2-methacryloyloxyethyl D-mannopyranoside (ME Man, alpha:beta = 6.5:3.5) using a lipophilic radical initiator. The mannos e-carrying amphiphiles (DODA-PMEMan, DP (degree of polymerization) = 3, 8, 14, and 17) incorporated in liposomes were recognized by a lectin from Cana valia ensiformis (Con A), which was proven by the increase in turbidity of the liposome suspension after mixing with the lectin. The recognition was l argely affected by the degree of polymerization and surface density of the amphiphile in the liposomes. The association constant (K-as) between the ma nnose residue and Con A (2.2 x 10(5) M-1 for DODA-PMEMan (DP = 17) at 25 de greesC) was much larger than those for low molecular weight sugars (for exa mple, methyl alpha -D-mannopyranoside K-as = 8.2 x 10(3) M-1) due to the "c luster effect". Thermodynamic parameters showed a significant contribution of positive entropy change to the effective sugar recognition in the liposo me system, which was in contrast to the enthalpy-driven recognition of low molecular weight sugars by Con A. The positive entropy change could be attr ibuted to the "dehydration" of both Con A molecule and the mannose-carrying polymer chains which were fixed to the gigantic and hydrophilic liposome s urface.