Biophysical Society Thematic Meeting | Bucharest 2026

Biophysics of Membrane Reactions in Brian

Poster Abstracts

10-POS Board 10 CHOLESTEROL AND PEPTIDES IN BRAIN PHOSPHATIDYLCHOLINE BILAYERS Radha Ranganathan ; Miroslav Peric; California State University, Physics, Northridge, CA, USA A novel fluorescence anisotropy (FA) methodology was applied to determine cholesterol and Ab_peptide distributions and effects on lipid packing in brain phosphatidylcholine (PC), DPPC and POPC bilayers. Membrane fluidity and microdomains are critical for biological functions. Cholesterol regulates membrane lipid order. The probe Laurdan, senses polarity and is a molecular rotor with two conformational states in lipid bilayers. Gel phase conformer is parallel to the lipids. The naphthalene rings are near parallel to the bilayer plane in liquid disordered (Ld) phases. Emission, excited with vertically polarized light, was recorded with vertical (I VV ) and horizontal (I VH ) polarizers in the emitted beam. Sample temperature was 23°C, at which DPPC is in the gel phase and POPC and brain PC are supposedly in a single Ld phase. However, laurdan emission fit to two lognormal distributions in POPC and brain PC bilayers. Peaks at 450 and 490_nm indicate coexisting liquid ordered (Lo) and Ld phases. Computed second harmonic spectra were used for better fit precision. FA was calculated from intensities of resolved I VV and I VH lines. Thus, FA measured is conformer specific, unlike in conventional measurements where all conformers contribute to intensity at any chosen wavelength because of overlapping emissions, resulting in a composite FA. DPPC FA was 0.3. Lo phase FA in POPC or brain PC bilayers was 0.15. Without cholesterol, Ld phase conformer FA was 0.04 indicating a rotational correlation time much shorter than the fluorescence lifetime. Ld phase FA becomes negative above 20 % cholesterol, indicating cholesterol distribution to the Ld phase and further bend in the transition dipole. Ab_peptide exhibits similar behavior. Conformer and phase specific FA is novel and significant to molecular interactions in membranes.

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