Experiments measuring Fluorescence Resonance Energy Transfer (FRET) between cytokine receptor chains and their associated proteins led to hypotheses describing their organization in intact cells. These interactions occur within a larger protein complex or within a given nano-environment. To illustrate this complexity empirically, we developed a protocol to analyze FRET among more than two fluorescent proteins (multi-FRET). In multi-FRET, we model FRET among more than two fluorophores as the sum of all possible pairwise interactions within the complex. We validated our assumption by demonstrating that FRET among pairs within a fluorescent triplet resembled FRET between each pair measured in the absence of the third fluorophore. FRET between two receptor chains increases with increasing FRET between the ligand-binding chain (e.g., IFN-γR1, IL-10R1 and IFN-λR1) and an acylated fluorescent protein that preferentially resides within subsections of the plasma membrane. The interaction of IL-10R2 with IFN-λR1 or IL-10R1 results in decreased FRET between IL-10R2 and the acylated fluorescent protein. Finally, we analyzed FRET among four fluorescent proteins to demonstrate that as FRET between IFN-γR1 and IFN-γR2 or between IFN-αR1 and IFN-αR2c increases, FRET among other pairs of proteins changes within each complex.
Keywords: CFS; ChFP; CiFP; Confocal fluorescence spectroscopy; EGFP; EYFP; FP; FRET; IFN; IFN-α; IFN-γ; IFN-λ; Interferon receptor; Lipid raft; Multi-protein; OFP; ORF; PEI; StFP; TFP; ToFP; confocal fluorescence spectroscopy; enhanced green fluorescent protein; enhanced yellow fluorescent protein; fluorescence resonance energy transfer; fluorescent protein; interferon; interferon-α; interferon-γ; interferon-λ; mCherry/cherry fluorescent protein; mCitrine/monomeric citrine fluorescent protein; mOrange/orange fluorescent protein; mStrawberry/strawberry fluorescent protein; mTeal/teal fluorescent protein; open reading frame; polyethyleneimine; tdTomato/tomato fluorescent protein.
Copyright © 2013 Elsevier Ltd. All rights reserved.