Protein-Directed Spatial Rearrangement of Glycolipids at the Air−Water Interface for Bivalent Protein Binding: In Situ Infrared Reflection Absorption Spectroscopy

Lateral rearrangement of lipids on the surfaces of cell membranes plays an important role in multivalent interactions because a ligand for the second and subsequent binding events can be delivered through the lateral rearrangement. The binary monolayers containing glycolipids with mannose moieties at the air−water interface before and after binding of concanavalin A (Con A) have been investigated in detail using infrared reflection absorption spectroscopy (IRRAS). The spatial rearrangement of glycolipids in the binary monolayers directed by Con A in the subphase facilitated to match with protein binding pockets and minimize steric hindrance of neighboring carbohydrate ligands for bivalent protein binding. The amounts of specifically bound proteins were almost independent of surface glycolipid density at the air−water interface, different from the dependence of the amounts on surface ligand density at the solid−water interface with limited glycolipid rearrangement. Besides, hydrocarbon chains of the glycolipids in the monolayers were even reoriented favorable to the access of the ligands to the proteins for enhanced binding.