title: Coexistence of probe conformations in lipid phases-a polarized fluorescence microspectroscopy study.
abstract: Several well-established fluorescence methods depend on environment-sensitive probes that report about molecular properties of their local environment. For reliable interpretation of experiments, careful characterization of probes' behavior is required. In this study, bleaching-corrected polarized fluorescence microspectroscopy with nanometer spectral peak position resolution was applied to characterize conformations of two alkyl chain-labeled 7-nitro-2-1,3-benzoxadiazol-4-yl phospholipids in three model membranes, representing the three main lipid phases. The combination of polarized and spectral detection revealed two main probe conformations with their preferential fluorophore dipole orientations roughly parallel and perpendicular to membrane normal. Their peak positions were separated by 2-6 nm because of different local polarities and depended on lipid environment. The relative populations of conformations, estimated by a numerical model, indicated a specific sensitivity of the two probes to molecular packing with cholesterol. The coexistence of probe conformations could be further exploited to investigate membrane organization below microscopy spatial resolution, such as lipid rafts. With the addition of polarized excitation or detection to any environment-sensitive fluorescence imaging technique, the conformational analysis can be directly applied to explore local membrane complexity.
authors: Laboratory of Biophysics, Condensed Matter Physics Department, Jožef Stefan Institute, Ljubljana, Slovenia.
authors: Iztok
authors: I
authors: Urbančič
authors: Ajasja
authors: A
authors: Ljubetič
authors: Zoran
authors: Z
authors: Arsov
authors: Janez
authors: J
authors: Strancar
mesh_terms: D005454:Fluorescence Polarization / Q000379:methods*; D005456:Fluorescent Dyes / Q000737:chemistry*; D021962:Membrane Microdomains / Q000737:chemistry; D008968:Molecular Conformation; D010743:Phospholipids / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D010743:Phospholipids
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