Histidine7.36(305) in the conserved peptide receptor activation domain of the gonadotropin releasing hormone receptor couples peptide binding and receptor activation

Abstract

Transmembrane helix seven residues of G protein-coupled receptors (GPCRs) couple agonist binding to a conserved receptor activation mechanism. Amino-terminal residues of the GnRH peptide determine agonist activity. We investigated GnRH interactions with the His

Molecular basis for high affinity and selectivity of peptide antagonist, Bantag-1, for the orphan BB3 receptor

“…To gain insight into the molecular basis for the importance of histidine for high affinity Bantag-1 binding, a series of point mutations at position 107 in BB 3 receptor were made substituting amino acids with differing characteristics. Because the imidazole side-chain in histidine is reversibly protonated at physiological pH and the un-protonated form can exist in two different tautomeric structures, histidine can simultaneously form aromatic, hydrogen bonding, and salt bridge and charge-charge interactions [76]. With respect to the affect of the possible positive charge leading to charge-charge interactions, a number of our results support the conclusion it is not important for histidine in position 107 of the EC1 of BB 3 receptor for determining high affinity/selectivity for Bantag-1.…”

Gonadotropin-Releasing Hormone (GnRH) Receptor Structure and GnRH Binding

“…This led to a conclusion that Lys 3.32(121) may form a hydrogen bond with the aromatic rings of His 2 or Trp 3 of GnRH ( 37 , 99 ). Subsequent models proposed that Lys 3.32(121) contacts pGlu 1 or His 2 ( 37 , 68 , 110 – 113 ) but, in the absence of further experiments, it remains uncertain whether Lys 3.32(121) directly contacts GnRH or initiates receptor activation.…”

“…A Tyr 6.51(283) Phe mutation in the GnRH receptor and mutations of Phe 7.39(309) to Leu or Gln decreased GnRH-binding affinity ( 37 ). A recent computational model suggests that Phe 7.39(309) may contact Trp 3 of GnRH ( 110 ). Together, these data are consistent with the mutations disrupting ligand binding by breaking an interhelical contact between residues that may also contact the ligand, but more experiments are needed.…”

“…Molecular modeling showed that His 7.36(305) made only intramolecular contacts with the amino terminus of the receptor, whereas Trp 3 of GnRH was oriented near the consensus ligand-binding residue, Phe 7.39(308) . This suggests that His 7.36(305) forms an interhelical contact that positions Phe 7.39(308) to form π–π contact with Trp 3 of the peptide ( 110 ). The cHH-associated GnRH receptor mutation, Thr 32 Ile, which decreases ligand-binding affinity ( 63 ), is immediately adjacent to the His 7.36(305) interhelical contacts and may disrupt the interhelical contact.…”

Glu2.53(90) of the GnRH receptor is part of the conserved G protein-coupled receptor structure and does not form a salt-bridge with Lys3.32(121)

“…A one-way analysis of variance with post-hoc Tukey's test was used to determine whether pEC 50 and pIC 50 values for each mutant GnRH receptor differed from the values of the wild-type GnRH receptors. Coupling coefficients were calculated using the formula Q = 0.5 [(IC 50 + EC 50 )/EC 50 ](E max /B max ) using the data in Table 1, as previously described (J Ballesteros et al, 1998;Mayevu et al, 2015). Two-tailed T tests were used to compare interatomic distances in models of the wild-type and mutant GnRH receptors.…”