title: Quantitative multiphoton spectral imaging and its use for measuring resonance energy transfer.
abstract: Protein labeling with green fluorescent protein derivatives has become an invaluable tool in cell biology. Protein quantification, however, is difficult when cells express constructs with overlapping fluorescent emissions. Under these conditions, signal separation using emission filters is inherently inefficient. Spectral imaging solves this problem by recording emission spectra directly. Unfortunately, linear unmixing, the algorithm used for quantifying individual fluorophores from emission spectra, fails when resonance energy transfer (RET) is present. We therefore sought to develop an unmixing algorithm that incorporates RET. An equation for spectral emission incorporating RET was derived and an assay based on this formalism, spectral RET (sRET), was developed. Standards with defined RET efficiencies and with known Cerulean/Venus ratios were constructed and used to test sRET. We demonstrate that sRET analysis is a comprehensive, photon-efficient method for imaging RET efficiencies and accurately determines donor and acceptor concentrations in living cells.
authors.affiliation: National Institute of Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Thaler
authors.forename: Srinagesh V
authors.initials: SV
authors.lastname: Koushik
authors.forename: Paul S
authors.initials: PS
authors.lastname: Blank
authors.forename: Steven S
authors.initials: SS
authors.lastname: Vogel
mesh_terms: D000465:Algorithms; D000818:Animals; D016477:Artifacts; D001426:Bacterial Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002108:Ceruletide / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer / Q000379:methods*; D049452:Green Fluorescent Proteins; D007089:Image Enhancement / Q000379:methods; D008164:Luminescent Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D036641:Microscopy, Fluorescence, Multiphoton / Q000379:methods*; D009447:Neuroblastoma / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000032:analysis / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; C054562:yellow fluorescent protein, Bacteria; D049452:Green Fluorescent Proteins; D002108:Ceruletide