3 years ago

Quantifying intracellular equilibrium dissociation constants using single-channel time-resolved FRET

Quantifying intracellular equilibrium dissociation constants using single-channel time-resolved FRET
Banafshé Larijani, Jose Requejo-Isidro, Gloria de las Heras-Martínez, Josu Andrieu
Quantification of the intracellular equilibrium dissociation constant of the interaction, Kd, is challenging due to the variability of the relative concentrations of the interacting proteins in the cell. Fluorescence lifetime imaging microscopy (FLIM) of the donor provides an accurate measurement of the molecular fraction of donor involved in FRET, but the fraction of bound acceptor is also needed to reliably estimate Kd. We present a method that exploits the spectroscopic properties of the widely used eGFP – mCherry FRET pair to rigorously determine the intracellular Kd based on imaging the fluorescence lifetime of only the donor (single-channel FLIM). We have assessed the effect of incomplete labelling and determined its range of application for different Kd using Monte Carlo simulations. We have demonstrated this method estimating the intracellular Kd for the homodimerisaton of the oncogenic protein 3-phosphoinositide-dependent kinase 1 (PDK1) in different cell lines and conditions, revealing a competitive mechanism for its regulation. The measured intracellular Kd was validated against in-vitro data. This method provides an accurate and generic tool to quantify protein interactions in situ. We present a method that exploits the spectroscopic properties of the eGFP–mCherry FRET pair to rigorously determine the intracellular Kd of protein interactions based on single-channel FLIM. We have assessed the effect of incomplete labelling and established its range of application for different Kd. This method provides a robust and generic tool to quantify protein interactions in situ.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/jbio.201600272

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