Mechanical Stress Stimulates Conformational Changes in 5-Hydroxytryptamine Receptor 1B in Bone Cells

In this study we describe the conformational transitions of hydroxytryptamine receptor 1B (5HT1b) in response to ligand and fluid shear stress (FSS) stimulation. Fluorescence resonance energy transfer (FRET) and picosecond time-resolved fluorescence microscopy were employed to detect conformational changes in a genetically engineered 5HT1b receptor sensor containing an intramolecular GPCR conformation-sensitive FRET pair. Stimulation of 5HT1b sensor by a cognate ligand, 5-hydroxytryptamine (5HT), or the FSS led to distinct conformational changes characterized by an increase or decrease in FRET efficiency, respectively. The response to the FSS stimulation was inhibited in the presence of 5HT in the flow medium. Fluidization of the plasma membrane using benzyl alcohol stimulated 5HT1b conformational transitions characterized by decreased FRET levels. Our study provides the first evidence of (1) ligand-independent conformational response of the 5HT1b to mechanical perturbation and (2) modulation of such mechanosensitive response by the cognate ligand.