Protease-activated receptor signalling initiates α5ß1-integrin-mediated adhesion in non-haematopoietic cells.

Haematopoietic cells and platelets employ G-protein-coupled receptors (GPCRs) to sense extracellular information and respond by initiating integrin-mediated adhesion. So far, such processes have not been demonstrated in non-haematopoietic cells. Here, we report that the activation of protease-activated receptors PAR1 and PAR2 induce multiple signalling pathways to establish α5ß1-integrin-mediated adhesion. First, PARs signal via Gßγ and PI3K to α5ß1-integrins to adopt a talin- and kindlin-dependent high-affinity conformation, which triggers fibronectin binding and initiates cell adhesion. Then, within 60 s, PARs signal via Gα13, Gαi, ROCK and Src to strengthen the α5ß1-integrin-mediated adhesion. Furthermore, PAR signalling changes the abundance of numerous proteins in the adhesome assembled by α5ß1-integrins, including Gα13, vacuolar protein-sorting-associated protein 36, and band 4.1-like protein 4B or 5, and accelerates cell adhesion maturation, spreading and migration. The mechanistic insights describe how agonist binding to PAR employs GPCR and integrin-signalling pathways to initiate and regulate adhesion and to guide physiological responses of non-haematopoietic cells.

Imaging G protein-coupled receptors while quantifying their ligand-binding free-energy landscape.

Imaging native membrane receptors and testing how they interact with ligands is of fundamental interest in the life sciences but has proven remarkably difficult to accomplish. Here, we introduce an approach that uses force-distance curve-based atomic force microscopy to simultaneously image single native G protein-coupled receptors in membranes and quantify their dynamic binding strength to native and synthetic ligands. We measured kinetic and thermodynamic parameters for individual protease-activated receptor-1 (PAR1) molecules in the absence and presence of antagonists, and these measurements enabled us to describe PAR1's ligand-binding free-energy landscape with high accuracy. Our nanoscopic method opens an avenue to directly image and characterize ligand binding of native membrane receptors.

Seeing and sensing single G protein-coupled receptors by atomic force microscopy.

G protein-coupled receptors (GPCRs) relay extracellular information across cell membranes through a continuum of conformations that are not always captured in structures. Hence, complementary approaches are required to quantify the physical and chemical properties of the dynamic conformations linking to GPCR function. Atomic force microscopy (AFM)-based high-resolution imaging and force spectroscopy are unique methods to scrutinize GPCRs and to sense their interactions. Here, we exemplify recent AFM-based applications to directly observe the supramolecular assembly of GPCRs in native membranes, to measure the ligand-binding free-energy landscape, and how interactions modulate the structural properties of GPCRs. Common trends in GPCR function are beginning to emerge. We envision that technical developments in combining AFM with superresolution fluorescence imaging will provide insights into how cellular states modulate GPCRs and vice versa.

Conformational Plasticity of Human Protease-Activated Receptor 1 upon Antagonist- and Agonist-Binding.

G protein-coupled receptors (GPCRs) show complex relationships between functional states and conformational plasticity that can be qualitatively and quantitatively described by contouring their free energy landscape. However, how ligands modulate the free energy landscape to direct conformation and function of GPCRs is not entirely understood. Here, we employ single-molecule force spectroscopy to parametrize the free energy landscape of the human protease-activated receptor 1 (PAR1), and delineate the mechanical, kinetic, and energetic properties of PAR1 being set into different functional states. Whereas in the inactive unliganded state PAR1 adopts mechanically rigid and stiff conformations, upon agonist or antagonist binding the receptor mechanically softens, while increasing its conformational flexibility, and kinetic and energetic stability. By mapping the free energy landscape to the PAR1 structure, we observe key structural regions putting this conformational plasticity into effect. Our insight, complemented with previously acquired knowledge on other GPCRs, outlines a more general framework to understand how GPCRs stabilize certain functional states.

Structural Properties of the Human Protease-Activated Receptor 1 Changing by a Strong Antagonist.

The protease-activated receptor 1 (PAR1), a G protein-coupled receptor (GPCR) involved in hemostasis, thrombosis, and inflammation, is activated by thrombin or other coagulation proteases. This activation is inhibited by the irreversible antagonist vorapaxar used for anti-platelet therapy. Despite detailed structural and functional information, how vorapaxar binding alters the structural properties of PAR1 to prevent activation is hardly known. Here we apply dynamic single-molecule force spectroscopy to characterize how vorapaxar binding changes the mechanical, kinetic, and energetic properties of human PAR1 under physiologically relevant conditions. We detect structural segments stabilizing PAR1 and quantify their properties in the unliganded and the vorapaxar-bound state. In the presence of vorapaxar, most structural segments increase conformational variability, lifetime, and free energy, and reduce mechanical rigidity. These changes highlight a general trend in how GPCRs are affected by strong antagonists.