Binding Conformation and Kinetics of Two Pheromone-Binding Proteins from the Gypsy Moth Lymantria dispar with Biological and Nonbiological Ligands

摘要

Pheromone-binding proteins (PBPs) in insects can bind various substances and selectively delivernthemessage of a signalmolecule to the downstreamcomponents of the olfactory system. This can be achievedneither through a ligand-specific conformational change of the C-terminal peptide of the PBP or by selectivelynbinding/releasing the ligand. PBP may also act as a scavenger to protect the sensory neurons from saturatingnat high ligand doses.We have compared two PBPs fromthe gypsymoth (PBP1 and PBP2) and their truncatednforms (TPBPs), which lack the C-terminal peptide, in this study. Stopped-flow kinetics with N-phenyl-1-nnaphthylamine (NPN) have revealed a diffusion-controlled collisional step, between PBP and NPN, afternwhich the NPN relocates into a hydrophobic environment. This work supports the hypothesis that bindingnbetween PBPs and ligands occurs stepwise. With the method of tryptophan fluorescence quenching, we havenshown different local conformational changes around Trp 37, induced by different ligands, manifested innchanges of both the steric and electronic environment around the residue. Importantly, we have noticed ansignificant difference in the changes induced by the biological ligand (the pheromone) and nonbiologicalnligands. Therefore, we hypothesize that PBP may serve a different function in each kinetic step, displaying anunique P 3nL conformation