Protein-mediated restructuring of lipid domains. Topography in myelin monolayers

RAFAEL GUSTAVO OLIVEIRA; ROSETTI, C. M.; MAGGIO, B.

Madrid, España

Congreso; VI Ibero-American Congress of Biophysics; 2006

SOBLA

Purified myelin can be spread as Langmuir monomolecular layers at the air/water interface. The chemical composition remains unaltered after spreading. Though both hemilayers of the membrane are mixed, the main advantage of using monomolecular films is that variation of lateral molecular packing can be done in a controlled manner with the simultaneous measurement of surface pressure, surface potential, as well as reflectance. From the compression isotherms, phase coexistence could not be revealed; however, microscopic observation by fluorescence, Brewster angle microscopy and immunolabelling, allows to detect that there are at least two phases over the whole compression range up to 47 mN/m (the monolayer collapse pressure). Myelin is composed of lipids (75 % in mass) and proteins (25 %), being the proteins mainly constituted by Folch?s proteolipid (PLP 50 % of the protein mass) and myelin basic protein (MBP, 30 %). The protein-free lipid fraction does not display the phase coexistence above a surface pressure of 1-3mN/m. The phase coexistence and different aspects of the surface topography of whole myelin monolayer are contributed by the two major myelin proteins.  The general fractal structure, better observed at high surface pressures, is due to the structuring by PLP. On the other hand, MBP induces liquid and round-shaped domains mainly adsorbing to and/or mixing with the fractal boundaries.
PLP and MBP induce domain structuring in an independent way, and the addition of both proteins to the lipid extract re-establishes the pattern of the whole myelin monolayer.