Sodium Dodecyl Sulfate−Polyacrylamide Gel Electrophoresis and Förster Resonance Energy Transfer Suggest Weak Interactions between Fibroblast Growth Factor Receptor 3 (FGFR3) Transmembrane Domains in the Absence of Extracellular Domains and Ligands

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Abstract
Lateral dimerization of membrane proteins has evolved as a means of signal transduction across the plasma membrane for all receptor tyrosine kinases (RTKs). The transmembrane (TM) domains of RTKs are proposed to play an important role in the dimerization process. We have investigated whether the TM domains of one RTK, fibroblast growth factor receptor 3 (FGFR3), dimerize in lipid vesicles in the absence of the extracellular domains and ligands. We have performed sodium dodecyl sulfate−polyacrylamide gel electrophoresis (SDS−PAGE) with peptides produced via solid-phase peptide synthesis that correspond to the TM domain of FGFR3. We have carried out Förster resonance energy transfer (FRET) measurements using two donor−acceptor pairs, fluorescein/rhodamine and Cy3/Cy5, as a function of peptide concentration and donor-to-acceptor mole ratios. Our results suggest that FGFR3 TM domains form sequence-specific dimers in lipid bilayers. However, the dimerization propensity of FGFR3 TM domain is much weaker than the dimerization propensity of glycophorin A (GpA), the well-characterized “membrane dimer standard”. We discuss our findings in the context of cell signaling across the plasma membrane and diseases or disorders that occur due to single amino acid mutations in the TM domain of FGFR3.