Production, crystallization and preliminary X-ray diffraction of the Gαs α-helical domain in complex with a nanobody

GPCR–G-protein complexes are one of the most important components of cell-signalling cascades. Extracellular signals are sensed by membrane-associated G-protein-coupled receptors (GPCRs) and transduced via G proteins towards intracellular effector molecules. Structural studies of these transient complexes are crucial to understand the molecular details of these interactions. Although a nucleotide-free GPCR–G-protein complex is stable, it is not an ideal sample for crystallization owing to the intrinsic mobility of the Gαs α-helical domain (AHD). To stabilize GPCR–G-protein complexes in a nucleotide-free form, nanobodies were selected that target the flexible GαsAHD. One of these nanobodies, CA9177, was co-crystallized with the GαsAHD. Initial crystals were obtained using the sitting-drop method in a sparse-matrix screen and further optimized. The crystals diffracted to 1.59 Å resolution and belonged to the monoclinic space group P2₁, with unit-cell parameters a = 44.07, b = 52.55, c = 52.66 Å, α = 90.00, β = 107.89, γ = 90.00°. The structure of this specific nanobody reveals its binding epitope on GαsAHD and will help to determine whether this nanobody could be used as crystallization chaperone for GPCR–G-protein complexes.