NMR Structure of Navel Orangeworm Moth Pheromone-Binding Protein (AtraPBPI): Implications for pH-Sensitive Pheromone Detection

摘要

The navel orangeworm, Amyelois transitella(Walker). is an agricultural insect pesthat can be controlled by disrupting male-female communication with sex pheromones, a technique known as mating disruption. Insect pheromone-binding proteins (PBPs) provide fast transport of hydrophobic pheromones through the aqueous sensillar lymph and promote sensitive delivery of pheromones to receptors. Here we present the three-dimensional structure of a PBP from A. transitella (AtraPBP1) in solution at pH 4.5 determined by nuclear magnetic resonance (NMR) spectroscopy. Pulsed-field gradient NMR diffusion experiments, multiangle light scattering, and ~(1N5NMR relaxation analys)is indicate that AtraPBPI forms a stable monomer in solution at pH 4.5 in contrast to forming mostly dimers at pH 7. The NMR structure of AtraPBP I at pH 4.5 contains seven a-helices (al, L8- L23; a2, D27- F36; a3, R46- V62; a4, A73- M78; a5, D84-SI00; α6, R107-L125; a7. M131-E141) that adopt an overall main-chain fold similar to that of PBPs found in Antheraea polyphemusand Bombyxmorl. The AtraPBPI structure is stabilized by three disulfide bonds formed by C19/C54, C50/C108, and C97/C1I7 and salt bridges formed by H69/ E60, H70/E57, H80/E132, H95/E141, and H123/D40. All five His residues are cationic at pH 4.5, whereas H80 and H95 become neutral at pH 7.0. The C-terminal helix (a7) contains hydrophobic residues (M131, V133, V134, V135, V138, L139, and A140) that contact conserved residues (W37, L59, A73, F76, A77, 194, V111 , and V115) suggested to interact with bound pheromone. Our NMR studies reveal that acid-induced formation of the C-terminal helix at pH 4.5 is triggered by a histidine protonation switch that promotes rapid release of bound pheromone under acidic conditions.