title: Automated Analysis of Single-Molecule Photobleaching Data by Statistical Modeling of Spot Populations.
abstract: The number of fluorophores within a molecule complex can be revealed by single-molecule photobleaching imaging. A widely applied strategy to analyze intensity traces over time is the quantification of photobleaching step counts. However, several factors can limit and bias the detection of photobleaching steps, including noise, high numbers of fluorophores, and the possibility that several photobleaching events occur almost simultaneously. In this study, we propose a new approach, to our knowledge, to determine the fluorophore number that correlates the intensity decay of a population of molecule complexes with the decay of the number of visible complexes. We validated our approach using single and fourfold Atto-labeled DNA strands. As an example we estimated the subunit stoichiometry of soluble CD95L using GFP fusion proteins. To assess the precision of our method we performed in silico experiments showing that the estimates are not biased for experimentally observed intensity fluctuations and that the relative precision remains constant with increasing number of fluorophores. In case of fractional fluorescent labeling, our simulations predicted that the fluorophore number estimate corresponds to the product of the true fluorophore number with the labeling fraction. Our method, denoted by spot number and intensity correlation (SONIC), is fully automated, robust to noise, and does not require the counting of photobleaching events.
authors.affiliation: Division of Theoretical Bioinformatics (B080), German Cancer Research Center (DKFZ), Heidelberg, Germany; Department for Bioinformatics and Functional Genomics, Institute for Pharmacy and Molecular Biotechnology (IPMB) and BioQuant, Heidelberg University, Heidelberg, Germany.
authors.forename: Clarissa
authors.initials: C
authors.lastname: Liesche
authors.affiliation: CellNetworks Cluster and Institute for Physical Chemistry, BioQuant, Heidelberg University, Heidelberg, Germany.
authors.forename: Kristin S
authors.initials: KS
authors.lastname: Grussmayer
authors.affiliation: CellNetworks Cluster and Institute for Physical Chemistry, BioQuant, Heidelberg University, Heidelberg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Ludwig
authors.affiliation: Division of Theoretical Bioinformatics (B080), German Cancer Research Center (DKFZ), Heidelberg, Germany; Department for Bioinformatics and Functional Genomics, Institute for Pharmacy and Molecular Biotechnology (IPMB) and BioQuant, Heidelberg University, Heidelberg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Wörz
authors.affiliation: Division of Theoretical Bioinformatics (B080), German Cancer Research Center (DKFZ), Heidelberg, Germany; Department for Bioinformatics and Functional Genomics, Institute for Pharmacy and Molecular Biotechnology (IPMB) and BioQuant, Heidelberg University, Heidelberg, Germany.
authors.forename: Karl
authors.initials: K
authors.lastname: Rohr
authors.affiliation: CellNetworks Cluster and Institute for Physical Chemistry, BioQuant, Heidelberg University, Heidelberg, Germany.
authors.forename: Dirk-Peter
authors.initials: DP
authors.lastname: Herten
authors.affiliation: Division of Theoretical Bioinformatics (B080), German Cancer Research Center (DKFZ), Heidelberg, Germany; Department for Bioinformatics and Functional Genomics, Institute for Pharmacy and Molecular Biotechnology (IPMB) and BioQuant, Heidelberg University, Heidelberg, Germany.
authors.forename: Joël
authors.initials: J
authors.lastname: Beaudouin
authors.affiliation: Division of Theoretical Bioinformatics (B080), German Cancer Research Center (DKFZ), Heidelberg, Germany; Department for Bioinformatics and Functional Genomics, Institute for Pharmacy and Molecular Biotechnology (IPMB) and BioQuant, Heidelberg University, Heidelberg, Germany. Electronic address: r.eils@dkfz.de.
authors.forename: Roland
authors.initials: R
authors.lastname: Eils
mesh_terms: D001331:Automation; D001483:Base Sequence; D004247:DNA / Q000737:chemistry / Q000235:genetics; D005456:Fluorescent Dyes / Q000737:chemistry*; D007091:Image Processing, Computer-Assisted; D008853:Microscopy; D008958:Models, Molecular; D015233:Models, Statistical; D009690:Nucleic Acid Conformation; D038761:Photobleaching; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D019014:fas Receptor / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D019014:fas Receptor; D004247:DNA