STRUCTURALLY ALTERED STATES OF PURIFIED MYELIN UNDER DIFFERENT CONDITIONS: AN XRAY AND NEUTRON SCATTERING STUDY

PUSTERLA, JULIO M.; SCHNECK, E.; FUNARI, SÉRGIO S.; DEMÉ, B.; PABLO J. YUNES QUARTINO; TANAKA, M.; OLIVEIRA, RAFAEL G.

Villa Carlos Paz

Otro; Current Advances on Neurodegeneration: From Molecular Biology to Translational Medicine; 2017

Alumni Club Argentina Alexander von Humboldt CLUB-AR

Myelin is the spiral membrane surrounding axons and providing for fast and efficient nerve impulse propagation. Preservation of its structure is a pre-requisite for its normal function. Here we assess some altered states by employing scattering techniques. SAXS of myelin membrane suspensions allows us to determine the influence of cooling and salts in combination over the homogeneity/heterogeneity of the membrane, as manipulated upon detergent-insoluble glycosphingolipid-rich domains (DIGs). SAXS and Neutron Diffraction consistently show that multilamellar purified myelin membranes (PMMs) in pure water become heterogeneous when cooled by more than 10 ? 15 °C below physiological temperature, as during the DIGs isolation procedure. The heterogeneous state of PMMs is stabilized in physiological solution, where phase coexistence persists up to near the physiological temperature. This result supports the general view that membranes under physiological conditions are close to critical points for phase separa􀆟on. In presence of elevated Ca2+ concentrations (> 10 mM), phase coexistence is found even far above physiological temperatures. The relative fractions of the two phases, and thus presumably also their compositions, are found to vary with temperature. Depending on the conditions, an ?expanded? phase with larger lamellar period or a ?compacted? phase with smaller lamellar period coexists with the native phase. Phospholipases account for a defined partial expansion of the periodicity between membranes by about 2 nm. The spreading of multilayers over solid substrate allows the splitting of components of the vector scattering in a diffraction geometry. In principle, mechanical properties (Bending Rigidity and Perpendicular Compressibility) of the membrane stack and its particular phases can be accounted from the specular and off-specular dispersion. These studies are manly basic but with potential applicability to pathological situations.