NMR assignment of the A form of the pheromone-binding protein of Bombyx mori

Backbone and side chain NMR assignments and secondary structure calculation of the pheromone binding protein3 of Ostrinia nubilalis, an agricultural pest

Ostrinia nubilalis, also known as European Corn Borer (ECB), is a serious pest in Europe and North America, as well as in Central Asia and Northern Africa. It damages a variety of agricultural crops such as corn, oats, buckwheat, millet, and soybeans. causing annually at least one billion dollars in loss. The Ostrinia nubilalis pheromone-binding protein3 (OnubPBP3), preferentially expressed in the male moth antenna, has been implicated in the detection of the female-secreted pheromone blend during the mating process. Understanding the structure of and function of OnubPBP3, including the mechanism of pheromone binding and its release at the dendritic olfactory neuron (ORN), is essential if integrated pest management through sensory inhibition is to be achieved. We report here the backbone and side-chain resonance assignments of OnubPBP3 at pH 6.5 using various triple resonance NMR experiments on a 13C, 15N-labeled protein sample. The secondary structure of OnubPBP3 consists of six α-helices and an unstructured C-terminus based on backbone chemical shifts.

1H, 13C, and 15N resonance assignment and secondary structure of the pheromone-binding protein2 from the agricultural pest Ostrinia furnacalis (OfurPBP2)

Ostrinia furnacalis, a lepidopteran moth, is an invasive pest found in Asia, Australia, Africa, and parts of the United States. The O. furnacalis pheromone-binding protein2 (OfurPBP2), present in the male moth antenna, plays a role in the detection of female-secreted pheromone in a process that leads to mating. To understand the structural mechanism of pheromone binding and release in this pest, we have initiated characterization of OfurPBP2 by solution NMR. Here, we report the backbone resonance assignments and the secondary structural elements of OfurPBP2 at pH 6.5 using uniformly ¹³C, ¹⁵N-labeled protein with various triple resonance NMR experiments. The assignments are 97% completed for backbone and 88% completed for side-chain resonances. The secondary structure of OfurPBP2, based on backbone chemical shifts, consists of eight α-helices, including a well-structured C-terminal helix.

Pheromone Binding Protein EhipPBP1 Is Highly Enriched in the Male Antennae of the Seabuckthorn Carpenterworm and Is Binding to Sex Pheromone Components

The seabuckthorn carpenterworm moth Eogystia hippophaecolus is a major threat to seabuckthorn plantations, causing considerable ecological and economic losses in China. Transcriptomic analysis of E. hippophaecolus previously identified 137 olfactory proteins, including three pheromone-binding proteins (PBPs). We investigated the function of E. hippophaecolus PBP1 by studying its mRNA and protein expression profiles and its binding ability with different compounds. The highest levels of expression were in the antennae, particularly in males, with much lower levels of expression in the legs and external genitals. Recombinant PBP1 showed strong binding to sex-pheromone components, suggesting that antennal EhipPBP1 is involved in binding sex-pheromone components during pheromone communication.

Kinetics of olfactory responses might largely depend on the odorant-receptor interaction and the odorant deactivation postulated for flux detectors

Experimental data together with modeling of pheromone perireceptor and receptor events in moths (Bombyx mori, Antheraea polyphemus) suggest that the kinetics of olfactory receptor potentials largely depend on the association of the odorant with the neuronal receptor molecules and the deactivation of the odorant accumulated around the receptor neuron. The first process could be responsible for the reaction times (mean about 400 ms) of the nerve impulses at threshold. The second process has been postulated for flux detectors such as olfactory sensilla of moths. The odorant deactivation could involve a modification of the pheromone-binding protein (PBP) that "locks" the pheromone inside the inner binding cavity of the protein. The model combines seemingly contradictory functions of the PBP such as pheromone transport, protection of the pheromone from enzymatic degradation, pheromone deactivation, and pheromone-receptor interaction. Model calculations reveal a density of at least 6,000 receptor molecules per µm(2) of neuronal membrane. The volatile decanoyl-thio-1,1,1-trifluoropropanone specifically blocks pheromone receptor neurons, probably when bound to the PBP and by competitive binding to the receptor molecules. The shallow dose-response curve of the receptor potential and altered response properties observed with pheromone derivatives or after adaptation may indicate shortened opening of ion channels.

Olfactory perireceptor and receptor events in moths: a kinetic model revised

Modelling reveals that within about 3 ms after entering the sensillum lymph, 17% of total pheromone is enzymatically degraded while 83% is bound to the pheromone-binding protein (PBP) and thereby largely protected from enzymatic degradation. The latter proceeds within minutes, 20,000-fold more slowly than with the free pheromone. In vivo the complex pheromone-PBP interacts with the receptor molecule. At weak stimulation the half-life of the active complex is 0.8 s due to the postulated pheromone deactivation. Most likely this process is enzymatically catalysed; it changes the PBP into a scavenger form, possibly by interference with the C-terminus. The indirectly determined PBP concentration (3.8 mM) is close to direct measurements. The calculated density of receptor molecules within the plasma membrane of the receptor neuron reaches up to 6,000 units per mum(2). This is compared with the estimated densities of the sensory-neuron membrane protein and of ion channels. The EC(50) of the model pheromone-PBP complex interacting with the receptor molecules is 6.8 muM, as compared with the EC(50) = 1.5 muM of bombykol recently determined using heterologous expression. A possible mechanism widening the range of stimulus intensities covered by the dose-response curve of the receptor-potential is proposed.

Structural basis of the honey bee PBP pheromone and pH-induced conformational change

The behavior of insects and their perception of their surroundings are driven, in a large part, by odorants and pheromones. This is especially true for social insects, such as the honey bee, where the queen controls the development and the caste status of the other individuals. Pheromone perception is a complex phenomenon relying on a cascade of recognition events, initiated in antennae by pheromone recognition by a pheromone-binding protein and finishing with signal transduction at the axon membrane level. With to the objective of deciphering this initial step, we have determined the structures of the bee antennal pheromone-binding protein (ASP1) in the apo form and in complex with the main component of the queen mandibular pheromonal mixture, 9-keto-2(E)-decenoic acid (9-ODA) and with nonpheromonal components. In the apo protein, the C terminus obstructs the binding site. In contrast, ASP1 complexes have different open conformations, depending on the ligand shape, leading to different volumes of the binding cavity. The binding site integrity depends on the C terminus (111-119) conformation, which involves the interplay of two factors; i.e. the presence of a ligand and a low pH. Ligand binding to ASP1 is favored by low pH, opposite to what is observed with other pheromone-binding proteins, such as those of Bombyx mori and Anopheles gambiae.

Identification and molecular cloning of putative odorant-binding proteins and chemosensory protein from the bethylid wasp, Scleroderma guani Xiao et Wu

Two putative odorant-binding proteins (OBPs) and one putative chemosensory protein (CSP) from females of the ant-like bethylid wasp, Scleroderma guani Xiao et Wu (Hymenoptera: Bethylidae), were identified and cloned. The putative OBPs and CSP were identified by nondenaturing polyacrylamide gel electrophoresis (native-PAGE). 3' rapid amplification of cDNA ends (3'RACE) was performed to obtain the sequences of the mature proteins by using degenerate primers designed from N-terminal sequences. Gene-specific primers for 5' rapid amplification of cDNA ends (5'RACE) were designed according to 3'RACE results and used in polymerase chain reaction (PCR) to obtain full-length sequences. The proteins (Sgua-OBP1, Sgua-OBP2, and Sgua-CSP1) encode 133, 142, and 129 amino acid-deduced sequences, respectively. Prediction of signal peptide sequences matches the N-terminal amino acid sequence of the isolated proteins. Database searches suggest that the Sgua-OBP1 and Sgua-OBP2 are homologs of OBPs from other insects, and Sgua-CSP1 shares a high level of identity with previously described CSPs.

Sulfur single-wavelength anomalous diffraction crystal structure of a pheromone-binding protein from the honeybee Apis mellifera L

Pheromone binding proteins (PBPs) are small helical proteins ( approximately 13-17 kDa) present in several sensory organs from moth and other insect species. They are involved in the transport of pheromones from the sensillar lymph to the olfactory receptors. We report here the crystal structure of a PBP (Amel-ASP1) originating from the honey-bee (Apis mellifera) antennae and expressed as recombinant protein in the yeast Pichia pastoris. Crystals of Amel-ASP1 were obtained at pH 5.5 using the nano-drops technique of crystallization with a novel optimization procedure, and the structure was solved initially with the single-wavelength anomalous diffraction technique using sulfur anomalous dispersion. The structure of Amel-ASP1 has been refined at 1.6-A resolution. Its fold is roughly similar to that of other PBP/odorant binding proteins, presenting six helices and three disulfide bridges. Contrary to the PBPs from Bombyx mori (Sandler, B. H., Nikonova, L., Leal, W. S., and Clardy, J. (2000) Chem. Biol. 7, 143-151) and Leucophea maderae (Lartigue, A., Gruez, A., Spinelli, S., Riviere, S., Brossut, R., Tegoni, M., and Cambillau, C. (2003) J. Biol. Chem. 278, 30213-30218), the extended C terminus folds into the protein and forms a wall of the internal hydrophobic cavity. Its backbone groups establish two hydrogen bonds with a serendipitous ligand, n-butyl-benzene-sulfonamide, an additive used in plastics. This mode of binding might, however, mimic that used by one of the pheromonal blend components and illustrates the binding versatility of PBPs.

Conformational isomers of insect odorant-binding proteins

We have identified and cloned the cDNAs encoding odorant-binding proteins (OBPs) from the large black chafer, Holotrichia parallela, and the yellowish elongate chafer, Heptophylla picea. Each species possess two OBPs, the proteins migrating faster in native gels (OBP1) showed high amino acid identity (>88%) to previously identified pheromone-binding proteins (PBPs) from scarab beetles. HparOBP1 and HpicOBP1 have 116 amino acids and six highly conserved cysteine residues. In contrast to OBP1 that gave a single band, both HparOBP2 and HpicOBP2 separated each into two bands in native gels (15%). The N-terminal amino acid sequences for the two bands from each species were indistinguishable, and they had the same molecular masses. Although we sequenced several clones from each species, they all encode only one protein for each species, indicating they are different conformational isomers of the same protein. HparOBP2 and HpicOBP2 have 133 amino acids and cysteine residues are conserved in proteins of the same family.

NMR structure reveals intramolecular regulation mechanism for pheromone binding and release

Odorants are transmitted by small hydrophobic molecules that cross the aqueous sensillar lymph surrounding the dendrites of the olfactory neurons to stimulate the olfactory receptors. In insects, the transport of pheromones, which are a special class of odorants, is mediated by pheromone-binding proteins (PBPs), which occur at high concentrations in the sensillar lymph. The PBP from the silk moth Bombyx mori (BmPBP) undergoes a pH-dependent conformational transition between the forms BmPBP(A) present at pH 4.5 and BmPBP(B) present at pH 6.5. Here, we describe the NMR structure of BmPBP(A), which consists of a tightly packed arrangement of seven alpha-helices linked by well defined peptide segments and knitted together by three disulfide bridges. A scaffold of four alpha-helices that forms the ligand binding site in the crystal structure of a BmPBP-pheromone complex is preserved in BmPBP(A). The C-terminal dodecapeptide segment, which is in an extended conformation and located on the protein surface in the pheromone complex, forms a regular helix, alpha(7), which is located in the pheromone-binding site in the core of the unliganded BmPBP(A). Because investigations by others indicate that the pH value near the membrane surface is reduced with respect to the bulk sensillar lymph, the pH-dependent conformational transition of BmPBP suggests a novel physiological mechanism of intramolecular regulation of protein function, with the formation of alpha(7) triggering the release of the pheromone from BmPBP to the membrane-standing receptor.

Isotopic double-labeling of two honeybee odorant-binding proteins secreted by the methylotrophic yeast Pichia pastoris

Odorant-binding proteins (OBPs) are soluble, low-molecular-weight proteins secreted in the sensillum lymph surrounding the dendrites of olfactory sensilla from a wide range of insect species. These proteins play a role in the solubilization, transport and/or deactivation of pheromones and odorants. In order to study the relationships between the molecular structure in solution and their ligand-binding properties, we have (13)C/(15)N-double-labeled two divergent honeybee OBPs, called ASP1 and ASP2, in sufficient quantities to permit a full determination of the structure and dynamics using heteronuclear NMR spectroscopy. The recombinant labeled proteins produced by the methylotrophic yeast Pichia pastoris have been secreted into a buffered minimal medium using native insect signal peptide. Mass spectrometry and Edman sequencing showed a native-like processing with a labeling efficiency of secreted proteins greater than 98%. After dialysis, the recombinant proteins were purified to homogeneity by one-step reversed-phase liquid chromatography. The final yield after 4-day shake-flask liquid culture was approximately 60 and 100 mg/L for ASP1 and ASP2, respectively. The inexpensive overproduction of labeled recombinant ASP1 and ASP2 should allow NMR studies of the structures and ligand-binding analysis in order to understand the relationships between structure and biological function of these proteins.