Evidence for activity-regulated hormone-binding cooperativity across glycoprotein hormone receptor homomers

Abstract

Glycoprotein hormone receptors show strong negative cooperativity. As a consequence, at physiological hormone concentrations, a single agonist binds to a receptor dimer. Here we present evidence that constitutively active receptors lose cooperative allosteric regulation in direct relation with their basal activity. The most constitutive mutants lost nearly all cooperativity and showed an increase of initial tracer binding, reflecting the ability of each protomer to bind with equal affinity. Allosteric interaction between the protomers takes place at the transmembrane domain. The allosteric message resulting from hormone binding to the ectodomain of one protomer travels 'downward' to its transmembrane domain, before affecting the transmembrane domain of the other protomer. This results in transmission of an 'upward' message lowering the binding affinity of the ectodomain of the second protomer. our results demonstrate a direct relation between the conformational changes associated with activation of the transmembrane domain and the allosteric behaviour of glycoprotein hormone receptors dimers.

Native Serotonin 5-HT2CReceptors Are Expressed as Homodimers on the Apical Surface of Choroid Plexus Epithelial Cells

“…Thus, the conformational change across the dimer interface following agonist binding to one protomer of a constitutively active homodimer would be less. This hypothesis is supported by a recent study demonstrating a direct link between cooperativity and basal activity for glycoprotein hormone receptors (Zoenen et al, 2012). The receptors displaying the highest levels of constitutive activity lost nearly all of their cooperative allosteric regulation.…”

G Protein–Coupled Receptor Multimers: A Question Still Open Despite the Use of Novel Approaches

“…Equilibrium and dissociation binding on these cells using both wild-type and engineered TSHR chimeras confirmed negative cooperativity between their orthosteric-binding sites, which is negatively correlated to the level of constitutive activity of the protomer (Zoenen et al, 2012). The chemokine receptors CCR2, CCR5, and CXCR4 form heteromers and display negativebinding cooperativity for their cognate chemokines in transfected cells (El-Asmar et al, 2005;Springael et al, 2006;Sohy et al, 2007Sohy et al, , 2009.…”

Oligomerization of GPCRs involved in endocrine regulation

“…The TSHR has been previously reported to homooligomerize (Latif et al 2001, Davies et al 2002, which is most likely independent from TSH stimulation (Bonomi & Persani 2013;Urizar et al 2005) or constitutive activation by mutation (Zoenen et al 2012, Biebermann et al 2012b. In regards to the TSHR, interaction between the receptor protomers occurs at the transmembrane bundle (Urizar et al 2005), but an additional role of the extracellular domain on the oligomer constitution is proposed based on BRET experiments ( Urizar et al 2005).…”

“…In TSHR, pathogenic mutations lead to diseased conditions such as congenital hypothyroidism or nonautoimmune hyperthyroidism, whereas in the LHCGR, male-limited precocious puberty (by CAMs) or hypogonadism may be associated with inactivating variants, although rare. CAMs of the TSHR have been proven on their impact on oligomerization and a direct modification of oligomeric states has not yet been confirmed (Zoenen et al 2012, Biebermann et al 2012b. This does not exclude the possibility that natural mutations in other receptors may indeed modulate oligomerization.…”

“…the LHCGR or TSHR per se as complexes. To date, there have been no difficulties in adequately combining or incorporating this property into current and previous mechanistical explanations of activation or inactivation, with few exceptions (Zoenen et al 2012). …”