Characterization of the aGPCR activation mechanism through their tethered agonist
Among the five classes of G protein-coupled receptors (GPCRs), the class of adhesion-GPCRs (aGPCRs) comprises the second largest but most mysterious one. Their activation mechanism and signal transduction is unsolved. We have recently identified an activating tethered peptide sequence for two members of the aGPCR family, the GPR126 and GPR133. This finding opens now the opportunity for differentiation between the CTF (C-terminal fragment)-mediated function (cis- signaling) and NTF (N-terminal fragment)-mediated function (trans- signal) of these receptors, which will help deciphering the very complex function of these two and other aGPCRs. In combination with our ongoing characterization of the G protein-dependent and –independent signaling cascades of all 33 human aGPCRs we aim to extend our survey for tethered agonists for other members of this class. Now, we are able to dissect the intracellular signal transduction cascades after receptor activation.
The rather long peptide sequences of 13 to 16 amino acids make in vivo testing approaches difficult. We aim to define the core region of the active peptide sequence to design smaller agonistic peptides or even small molecule agonists. Based on systematic mutagenesis of the known tethered agonists we will identify amino acids required for agonistic properties. The identification of the peptide-7TM interface (binding pocket) is another goal of our project.
The in vivo proof, that the identified peptide sequences are tethered agonists, is an important milestone in our investigation. Thus, in ex vivo studies the peptides will be tested on primary cell cultures from wild-type and aGPCR-deficient mice. For example, the maturation of Schwann cells will be studied after GPR126 activation. Taking advantage of established aGPCR-mutated mouse and zebrafish models we will test for rescue of disabled function using agonistic peptides.
Demberg LM, Winkler J, Wilde C, Simon KU, Schön J, Rothemund S, Schöneberg T, Prömel S, Liebscher I (2017) Activation of Adhesion G Protein-coupled Receptors: AGONIST SPECIFICITY OF STACHEL SEQUENCE-DERIVED PEPTIDES. J Biol Chem. 292:4383-4394.
Wilde C, Fischer L, Lede V, Kirchberger J, Rothemund S, Schöneberg T, Liebscher I (2016). The constitutive activity of the adhesion GPCR GPR114/ADGRG5 is mediated by its tethered agonist. FASEB J. 30:666-73.
Demberg LM, Rothemund S, Schöneberg T, and Liebscher I (2015) Identification of the tethered peptide agonist of the adhesion G protein-coupled receptor GPR64/ADGRG2. Biochem Biophys Res Commun (In press)
Hamann J, Aust G, Arac D, Engel FB, Formstone C, Fredriksson R, Hall RA, Harty BL, Kirchhoff C, Knapp B, Krishnan A, Liebscher I, Lin H-H, Martinelli DC, Monk KR, Peeters MC, Piao X, Prömel S, Schöneberg T, Schwartz TW, Singer K, Stacey M, Ushkaryov YA, Vallon M, Wolfrum U, Wright MW, Xu L, Langenhan T, and Schiöth HB (2015) International Union of Basic and Clinical Pharmacology. XCIV. Adhesion G Protein-Coupled Receptors. Pharmacological Reviews 67:338–367.
Petersen SC, Luo R, Liebscher I, Giera S, Jeong S-J, Mogha A, Ghidinelli M, Feltri ML, Schöneberg T, Piao X, and Monk KR (2015) The Adhesion GPCR GPR126 Has Distinct, Domain-Dependent Functions in Schwann Cell Development Mediated by Interaction with Laminin-211. Neuron 85:755–769.
Liebscher I, Schön J, Petersen SC, Fischer L, Auerbach N, Demberg LM, Mogha A, Cöster M, Simon K-U, Rothemund S, Monk KR, and Schöneberg T (2014) A Tethered Agonist within the Ectodomain Activates the Adhesion G Protein-Coupled Receptors GPR126 and GPR133. Cell Reports 9:2018–2026.