Insights into differential modulation of receptor function by hinge region using novel agonistic lutropin receptor and inverse agonistic thyrotropin receptor antibodies

We report two antibodies, scFv 13B1 and MAb PD1.37, against the hinge regions of LHR and TSHR, respectively, which have similar epitopes but different effects on receptor function. While neither of them affected hormone binding, with marginal effects on hormone response, scFv 13B1 stimulated LHR in a dose-dependent manner, whereas MAb PD1.37 acted as an inverse agonist of TSHR. Moreover, PD1.37 could decrease the basal activity of hinge region CAMs, but had varied effects on those present in ECLs, whereas 13B1 was refractory to any CAMs in LHR. Using truncation mutants and peptide phage display, we compared the differential roles of the hinge region cysteine box-2/3 as well as the exoloops in the activation of these two homologus receptors.

► First report of novel agonistic and antagonistic scFvs against LHR hinge region.
► Discontinuous epitope of agonistic scFv comprises regions in both Cb-2 and Cb-3.
► Development of inverse agonistic MAb PD1.37 specific to Cb-3 of TSHR hinge region.
► Inhibition of basal activity of TSHR activating mutations by MAb PD1.37.
► Demonstration of differential interplay of hinge subdomains of LHR and TSHR.