Adsorption and Rheological Properties of Myelin Basic Protein and Effects On the Interaction Forces Between Myelin Bilayers

Abstract

Myelin Basic Protein (MBP) plays an important role in myelin structure, strongly holding the cytoplasmic membrane sides together mainly by electrostatic and hydrophobic interactions [1]. MBP is also known to affect lipid domains, increasing their size by lowering the line tension [2]. In this work, the rheological properties of MBPs between model myelin lipid bilayers and the effect of MBP on interaction forces are studied using the Surface Force Apparatus (SFA) technique. Results show that above a certain critical bulk concentration, Ccrit, MBP adsorbs abruptly on lipid membranes, forming a 3 nm - thick layer in which the viscosity is 2 to 3 times higher than the bulk MBP solution. Also, above this Ccrit, normal myelin membranes show higher adhesion and less repulsion compared to EAE (a model for multiple sclerosis) myelin lipid bilayers while below Ccrit, there was no evidence of MBP adsorption and no significant difference between the force profiles of normal (healthy) and EAE (diseased) myelin bilayers. These results suggest that MBP adsorbs “cooperatively” in clusters/domains to myelin bilayers, and provide new insights in to how lipid-protein domains affect inter-membrane interactions.