Weak Carbohydrate-Carbohydrate Interactions Measured by Colloidal Probe Microscopy

Abstract

The weak calcium mediated interaction between membrane based carbohydrates derived from the marine sponge Microciona prolifera has been investigated by colloidal probe microscopy. An in situ synthesis of glycolipids was employed to measure the dynamic strength of homomeric self-association between sulfated and non-sulfated oligosaccharides. For this purpose an in situ protocol has been developed to entirely rely on a defined synthetic system with adjustable composition and physical properties. Since thermal undulation of membranes renders analysis of binding affinity cumbersome we rely on solid supported membranes with preserved fluidity and minimal non-specific interaction. We investigate the attraction of carbohydrates derived from Microciona prolifera with a focus on the role of calcium ions, the necessity of the sulfate group, membrane fluidity, and loading rate. Membrane fluidity is of particular interest considering that lateral organization of ligand-receptors into small-scale clusters as a result of competition between binding enthalpy and mixing entropy is only possible in laterally mobile matrices.We found that nanoclusters consisting of 4-8 homomeric bonds were formed in the contact area between colloidal probe and solid supported membrane. Depletion of calcium or removal of the sulfato group resulted both in a disappearance of specific interactions.