Pheromone Perception: Mechanism of the Reversible Coil–Helix Transition in Antheraea polyphemus Pheromone-Binding Protein 1

Abstract

Pheromone-binding protein (PBP) in male moth antennae transports pheromone to the olfactory receptor neuron by undergoing a pH-dependent conformational switch, from PBP B at higher pH to PBP A at lower pH, associated with ligand binding and release, respectively. The characteristic feature of the dramatic protein switch is the pH-dependent reversible coil−helix transition of the C-terminus. In the PBP B conformation at pH >6.0, the C-terminus is exposed to the solvent as a coil while the ligand occupies the hydrophobic pocket. However, in the PBP A conformation at acidic pH, the C-terminus switches to a helix and releases the ligand by outcompeting it for the hydrophobic pocket. In Antheraea polyphemus PBP1 (ApolPBP1), the C-terminus (P 129 −V 142 ) is composed predominantly of hydrophobic residues except for three strategically located acidic residues: Asp 132 , Glu 137 , and Glu 141 . Here, we report for the first time on the consequences of the mutation of one or more acidic residues in the pH-driven reversible coil−helix transition of the ApolPBP1 C-terminus through biophysical characterization. Mutation of any single acidic residue in the C-terminus to its neutral counterpart destabilizes the helix formation at lower pH; these mutants exist as a mixture of both conformations. However, mutation of the two terminal acidic residues together knocks out the protein switch and adversely affects both ligand binding and release functions. Thus, these mutant proteins remain in the open (PBP B ) conformation at all pH levels.

Structural and Functional Characterization of European Corn Borer, Ostrinia nubilalis, Pheromone Binding Protein 3

“…Although OnubPBP3 shares over 50% sequence identity with several well-studied lepidopteran PBPs including ApolPBP1, − AtraPBP1, , BmorPBP, − and LdisPBPs , ­(Figure ), there are critical differences in two biological gates (highlighted in red in Figure ). The histidine gate is composed of His70 and His85 for these PBPs − (Figure ), however, in OnubPBP3, His70 is replaced by Arg70 (Figure ). Furthermore, the C-terminal gate (Pro128-Ser144) in OnubPBP3 is more polar than these PBPs − ­(Figure ).…”

“…The histidine gate is composed of His70 and His85 for these PBPs − (Figure ), however, in OnubPBP3, His70 is replaced by Arg70 (Figure ). Furthermore, the C-terminal gate (Pro128-Ser144) in OnubPBP3 is more polar than these PBPs − ­(Figure ). Similar differences have been reported in the primary structure of Ostrinia furnacalis pheromone binding protein2 (OfurPBP2) .…”

“…The male-biased OnubPBP3 has over 50% sequence identity to other well-studied lepidopteran PBPs from Antheraea polyphemus (ApolPBP1), − Amyelois transitella (AtraPBP1) , , Bombyx mori (BmorPBP), − and Lymantria dispar (LdisPBPs) , (Figure ). OnubPBP3 containing 144 residues has a calculated molecular mass of 16.3 kDa with a pI of 5.28 suggesting that this is a small acidic protein.…”

“…However, unlike the PBPs shown in Figure , OnubPBP3 has Arg70 in the place of a highly conserved His70, and the C-terminus is relatively more polar because of the presence of additional charged residues. Both His70 and the C-terminus are reported to play a critical role in ligand binding and release mechanisms of these well-characterized PBPs. − Thus, these substitutions in the OnubPBP3 primary sequence may have bearing on its structure and function.…”

Odorant Binding Proteins (OBPs) and Odorant Receptors (ORs) of Anopheles stephensi: Identification and comparative insights

“…In Antheraea polyphemus (polyphemus moth), first OBP was identified 40 years ago [ 16 ]. Binding of semiochemicals to OBPs is pH dependent wherein binding takes place at pH6.5 whereas bound chemicals are released from OBPs near ORs where the pH measures around 4.5 [ 17 – 20 ].…”