A single domain intrabody targeting the follicle-stimulating hormone receptor (FSHR) impacts FSH-induced G protein-dependent signalling

Intracellular variable fragments from heavy-chain antibody from camelids (intra-VHH) have been successfully used as chaperones to solve the 3D structure of active G protein-coupled receptors bound to their transducers. However, their effect on signalling has been poorly explored, although they may provide a better understanding on the relationships between receptor conformation and activity. Here, we isolated and characterized iPRC1, the first intra-VHH recognizing a member of the large glycoprotein hormone receptors family, the follicle-stimulating hormone receptor (FSHR). This intra-VHH recognizes the FSHR 3rd intracellular loop and decreases cAMP production in response to FSH, without altering Gαs recruitment. Hence, iPRC1 behaves as an allosteric modulator and provides a new tool to complete structure/activity studies performed so far on this receptor. ### Competing Interest Statement The authors have declared no competing interest. * GPCR : G protein-coupled receptor FSH : Follicle-stimulating hormone FSHR : FSH receptor LHCGR : Luteinizing hormone/choriogonadotropin receptor TSHR : Thyroid-stimulating hormone BSA : Bovine serum albumin BRET : Bioluminescence resonance energy transfer HTRF : Homogeneous time-resolved fluorescence ICL : intracellular loop AVP : Arginine-vasopressin AVPR2 : Arginine-vasopressin 2 receptor ISO : Isoproterenol hydrochloride ADRB2 : β2 adrenergic receptor Fsk : Forskolin PBS : Phosphate-buffered saline RLuc8 : luciferase from the sea pansy Renilla reniformis mGs : Mini Gs protein, minimal engineered GTPase domain of the Gα subunit APC : Allophycocyanine HEK293 : Human Embryonic Kidney 293