title: Dynamics imaging of lipid phases and lipid-marker interactions in model biomembranes.
abstract: Biomembranes are complex systems that regulate numerous biological processes. Lipid phases that constitute these membranes influence their properties and transport characteristics. Here, we demonstrate the potential of short-range dynamics imaging (excited-state lifetime, rotational diffusion, and order parameter) as a sensitive probe of lipid phases in giant unilamellar vesicles (GUVs). Liquid-disordered and gel phases were labeled with Bodipy-PC at room temperature. Two-photon fluorescence lifetime imaging microscopy of single-phase GUVs reveals more heterogeneity in fluorescence lifetimes of Bodipy in the gel phase (DPPC: 3.8+/-0.6 ns) as compared with the fluid phase (DOPC: 5.2+/-0.2 ns). The phase-specificity of excited-state lifetime of Bodipy-PC is attributed to the stacking of ordered lipid molecules that possibly enhances homo-FRET. Fluorescence polarization anisotropy imaging also reveals distinctive molecular order that is phase specific. The results are compared with DiI-C12-labeled fluid GUVs to investigate the sensitivity of our fluorescence dynamics assay to different lipid-marker interactions. Our results provide a molecular perspective of lipid phase dynamics and the nature of their microenvironments that will ultimately help our understanding of the structure-function relationship of biomembranes in vivo. Furthermore, these ultrafast excited-state dynamics will be used for molecular dynamics simulation of lipid-lipid, lipid-marker and lipid-protein interactions.
authors.affiliation: Department of Bioengineering, The Huck Institutes of the Life Sciences, The Pennsylvania State University, 231 Hallowell Building, University Park, Pennsylvania 16802, USA.
authors.forename: Florly S
authors.initials: FS
authors.lastname: Ariola
authors.forename: Deepti J
authors.initials: DJ
authors.lastname: Mudaliar
authors.forename: Ronn P
authors.initials: RP
authors.lastname: Walvick
authors.forename: Ahmed A
authors.initials: AA
authors.lastname: Heikal
mesh_terms: D016880:Anisotropy; D001672:Biocompatible Materials / Q000737:chemistry; D001896:Boron Compounds / Q000737:chemistry; D002627:Chemistry, Physical / Q000379:methods; D008051:Lipid Bilayers / Q000737:chemistry; D008055:Lipids / Q000737:chemistry*; D008560:Membrane Fluidity; D008566:Membranes / Q000737:chemistry*; D008567:Membranes, Artificial; D018613:Microscopy, Confocal; D015233:Models, Statistical; D011506:Proteins / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013696:Temperature
chemical_list: C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001672:Biocompatible Materials; D001896:Boron Compounds; D008051:Lipid Bilayers; D008055:Lipids; D008567:Membranes, Artificial; D011506:Proteins