title: A flexible approach to assess fluorescence decay functions in complex energy transfer systems.
abstract: BACKGROUND
  Time-correlated Förster resonance energy transfer (FRET) probes molecular distances with greater accuracy than intensity-based calculation of FRET efficiency and provides a powerful tool to study biomolecular structure and dynamics. Moreover, time-correlated photon count measurements bear additional information on the variety of donor surroundings allowing more detailed differentiation between distinct structural geometries which are typically inaccessible to general fitting solutions.
  
  
  RESULTS
  Here we develop a new approach based on Monte Carlo simulations of time-correlated FRET events to estimate the time-correlated single photon counts (TCSPC) histograms in complex systems. This simulation solution assesses the full statistics of time-correlated photon counts and distance distributions of fluorescently labeled biomolecules. The simulations are consistent with the theoretical predictions of the dye behavior in FRET systems with defined dye distances and measurements of randomly distributed dye solutions. We validate the simulation results using a highly heterogeneous aggregation system and explore the conditions to use this tool in complex systems.
  
  
  CONCLUSIONS
  This approach is powerful in distinguishing distance distributions in a wide variety of experimental setups, thus providing a versatile tool to accurately distinguish between different structural assemblies in highly complex systems.
authors.affiliation: Biochemistry and Biology, University of Potsdam, Potsdam, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Roethlein
authors.affiliation: Theoretical Physics, Free University Berlin, Berlin, Germany.
authors.forename: Markus S
authors.initials: MS
authors.lastname: Miettinen
authors.affiliation: Biochemistry and Biology, University of Potsdam, Potsdam, Germany ; Biochemistry and Molecular Biology, University of Hamburg, Hamburg, Germany.
authors.forename: Zoya
authors.initials: Z
authors.lastname: Ignatova
keywords: Complex heterogeneous systems; Monte-Carlo simulations; Protein aggregation; Time resolved FRET