(197e) Glycocalyx Osmolarity Modulates Macromolecular Binding to Cell Surfaces

The plasma membrane of mammalian cells is now understood to be a highly complex surface. Mass spectrometry, microscopy, and bioinformatics have revealed great diversity in size, composition, and post-translational modifications of cell surface glycoproteins and glycolipids. While physical crowding of the glycocalyx has been shown to induce membrane deformation, a clear understanding of the physical factors that contribute to crowding-associated phenomena remain unknown. In this talk, we demonstrate that 2D crowding of the cell surface glycocalyx directly modulates the binding affinity of soluble macromolecules to the plasma membrane. We introduce a set of molecular probes and use their binding isotherm to make a direct calculation of the in-plane osmotic pressure resulting from surface crowding. Importantly, we show that the osmotic pressure reduces the equilibrium binding affinity of an IgG antibody (among other macromolecules) to the surface, by up to a factor of ~7x, meaning that affinity is context dependent. Surprisingly, we find that negative charges contributed by sialic acid glycans decrease cell surface osmotic pressure far more than molecular weight or number density, accounting for ~50% of the reduction in affinity of IgG antibody on red blood cell membranes. We combine statistical mechanics theory, molecular simulations, and in-vitro reconstitution to highlight the impact of cell surface crowding on macromolecular binding and other cell behaviors mediated through the plasma membrane.

[Takatori S and Son S contributed equally to this work.]