Bacillus thuringiensis Cry1Ac toxin-binding and pore-forming activity in brush border membrane vesicles prepared from anterior and posterior midgut regions of lepidopteran larvae

In vivo and in silico comparison analyses of Cry toxin activities toward the sugarcane giant borer

The sugarcane giant borer, Telchin licus licus, is an insect pest that causes significant losses in sugarcane crops and in the sugar-alcohol sector. Chemical and manual control methods are not effective. As an alternative, in the current study, we have screened Bacillus thuringiensis (Bt) Cry toxins with high toxicity against this insect. Bioassays were conducted to determine the activity of four Cry toxins (Cry1A (a, b, and c) and Cry2Aa) against neonate T. licus licus larvae. Notably, the Cry1A family toxins had the lowest LC₅₀ values, in which Cry1Ac presented 2.1-fold higher activity than Cry1Aa, 1.7-fold larger than Cry1Ab, and 9.7-fold larger than Cry2Aa toxins. In silico analyses were performed as a perspective to understand putative interactions between T. licus licus receptors and Cry1A toxins. The molecular dynamics and docking analyses for three putative aminopeptidase N (APN) receptors (TlAPN1, TlAPN3, and TlAPN4) revealed evidence for the amino acids that may be involved in the toxin-receptor interactions. Notably, the properties of Cry1Ac point to an interaction site that increases the toxin's affinity for the receptor and likely potentiate toxicity. The interacting amino acid residues predicted for Cry1Ac in this work are probably those shared by the other Cry1A toxins for the same region of APNs. Thus, the presented data extend the existing knowledge of the effects of Cry toxins on T. licus licus and should be considered in further development of transgenic sugarcane plants resistant to this major occurring insect pest in sugarcane fields.

Synergistic interaction of Cry1Ah and Vip3Aa19 proteins combination with midgut ATP-binding cassette subfamily C receptors of Conogethes punctiferalis (Guenée) (Lepidoptera: Crambidae)

Bacillus thuringiensis Cry and Vip proteins are highly effective at controlling agricultural pests and could be used in pyramided transgenic crops. However, the molecular mechanism underlying the Cry1Ah and Vip3Aa19 synergistic interaction has never been investigated at the molecular level in Yellow peach moth (YPM) Conogethes punctiferalis. Binding affinity and synergism of Cry1Ah and Vip3Aa19 proteins with ABC transporter subfamily C receptors ABCC1, ABCC2 and ABCC3 proteins from the midgut of YPM larva by using surface plasmon resonance (SPR) and pull-down assays. Both assays revealed that Cry1Ah could interact with ABCC1, ABCC2, and ABCC3, whereas Vip3Aa19 only interacts with ABCC1 and ABCC3, but not with ABCC2. Hence, when compared to the Vip3Aa19 protein, Cry1Ah had a higher binding affinity for ABCC1, ABCC2, and ABCC3. Furthermore, competitive binding assay between Cry1Ah and Vip3Aa19 protein with ABC transporter subfamily C receptors resulted in the final eluted protein samples displaying vibrant blue bands of Cry1Ah and very faint bands of Vip3Aa19. Suggesting that Cry and Vip proteins could deliver a synergistic effect after cleaving the midgut proteases. Therefore, this finding indicated that the Cry1Ah and Vip3Aa19 do not compete for interacting with midgut receptors and thus provide strong synergism against YPM.

Analysis of Cry1Ah Toxin-Binding Reliability to Midgut Membrane Proteins of the Asian Corn Borer

Evolution of insect resistance to Bt toxins challenges the use of Cry toxins to control agricultural pests. In lepidopterans, Cry toxin affinity towards multiple midgut epithelial receptors has become a matter of dispute. Cry1Ah toxin-binding proteins were identified in the larval midgut of susceptible (ACB-BtS) and resistant (ACB-AhR) strains of the Asian corn borer (ACB). A pull-down assay was performed using biotinylated Cry1Ah toxin, and the binding proteins were identified by employing liquid chromatography–tandem mass spectrometry (LC-MS/MS). This study aimed to find the binding consistency of the midgut epithelial protein to the Cry1Ah toxin. The binding proteins from different fractions of SDS-PAGE showed a different pattern. We observed an isoform of prophenoloxidase PPO1b (UniProt Acc No. A0A1Q1MKI0), which was found only in the ACB-AhR fractions. Prophenoloxidase (proPO) is an extraordinary defense molecule activated in insect species during pathogen invasion and the wound healing process. Importantly, this prophenoloxidase might have direct/indirect interaction with the Cry1Ah toxin. Our data also suggest that factors like techniques, enrichment of binding proteins in the sample and the reversible and irreversible nature of the brush border membrane vesicles (BBMVs) to Cry toxins could cause the inconsistency in the protein–protein interactions. Moreover, inside the larva midgut, the influence of the Cry toxins under physiological conditions might be different from the laboratory procedures.

Identification of Cry1Ah-binding proteins through pull down and gene expression analysis in Cry1Ah-resistant and susceptible strains of Ostrinia furnacalis

Bacillus thuringiensis produces insecticidal Cry toxins used in the control of multiple insect pests. Evolution of insect resistance to Bt toxins endangers the use of Cry toxins for pest control. Analysis of the Cry1Ah-binding proteins from brush border membrane vesicles (BBMV) of Ostrinia furnacalis, Asian corn borer (ACB) from the Cry1Ah-resistant (ACB-AhR) and susceptible (ACB-BtS) strains was performed by an improved pull down assay that includes coupling Cry1Ah to NHS-activated Sepharose combined with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Our data show that Cry1Ah bound to alkaline phosphatase (ALP), cadherin-like (CAD), actin, aminopeptidase-N (APN), prophenoloxidase (proPO), serine proteinase inhibitor (SPI), immulectin, and V-ATPase and to other proteins that were not previously characterized as Cry-binding proteins in ACB-BtS strain. Analysis of Cry1Ah-pulled down proteins of the BBMV from ACB-AhR revealed that Cry1Ah toxin did not bind to ALP in ACB-AhR strain, suggesting that this protein may correlate with the resistant phenotype of this strain. Additionally, we analyzed the expression of representative genes coding for Cry1Ah-binding proteins such as ALP, APN, CAD, proPO, SPI, and immulectin by qRT-PCR. ACB-AhR showed increased expression levels of proPO (7.5 fold), ALP (6.2 fold) and APN (1.4 fold) in comparison to ACB-BtS strain. In contrast, the cad gene showed slight decreased expression in ACB-AhR strain (0.7 fold) compared with ACB-BtS strain. Our data suggest that differences in the susceptibility to Cry1Ah toxin in the ACB-AhR strain may be associated with reduced ALP binding sites and with an increased immune response. This study also brings evidence of a possible binding interaction of Cry1Ah toxin to immune related proteins like proPO.

Distribution of Glycan Motifs at the Surface of Midgut Cells in the Cotton Leafworm (Spodoptera littoralis) Demonstrated by Lectin Binding

Glycans are involved in many biological phenomena, including signal transduction, cell adhesion, immune response or differentiation. Although a few papers have reported on the role of glycans in the development and proper functioning of the insect midgut, no data are available regarding the localization of the glycan structures on the surface of the cells in the gut of insects. In this paper, we analyzed the spatial distribution of glycans present on the surface of the midgut cells in larvae of the cotton leafworm Spodoptera littoralis, an important agricultural pest insect worldwide. For this purpose, we established primary midgut cell cultures, probed these individual cells that are freely suspended in liquid medium with a selection of seven fluorescently labeled lectins covering a range of different carbohydrate binding specificities [mannose oligomers (GNA and HHA), GalNAc/Gal (RSA and SSA), GlcNAc (WGA and Nictaba) and Neu5Ac(α-2,6)Gal/GalNAc (SNA-I)], and visualized the interaction of these lectins with the different zones of the midgut cells using confocal microscopy. Our analysis focused on the typical differentiated columnar cells with a microvillar brush border at their apical side, which are dominantly present in the Lepidopteran midgut and function in food digestion and absorption, and as well as on the undifferentiated stem cells that are important for midgut development and repair. Confocal microscopy analyses showed that the GalNAc/Gal-binding lectins SSA and RSA and the terminal GlcNAc-recognizing WGA bound preferentially to the apical microvillar zone of the differentiated columnar cells as compared to the basolateral pole. The reverse result was observed for the mannose-binding lectins GNA and HHA, as well as Nictaba that binds preferentially to GlcNAc oligomers. Furthermore, differences in lectin binding to the basal and lateral zones of the cell membranes of the columnar cells were apparent. In the midgut stem cells, GNA and Nictaba bound more strongly to the membrane of these undifferentiated cells compared to the microvillar pole of the columnar cells, while SSA, HHA, WGA, and SNA-I showed stronger binding to the microvilli. Our results indicated that polarization of the midgut cells is also reflected by a specific distribution of glycans, especially between the basal and microvillar pole. The data are discussed in relation to the functioning and development of the insect midgut.

Toxicity and Binding Studies of Bacillus thuringiensis Cry1Ac, Cry1F, Cry1C, and Cry2A Proteins in the Soybean Pests Anticarsia gemmatalis and Chrysodeixis (Pseudoplusia) includens

Anticarsia gemmatalis (velvetbean caterpillar) and Chrysodeixis includens (soybean looper, formerly named Pseudoplusia includens) are two important defoliating insects of soybeans. Both lepidopteran pests are controlled mainly with synthetic insecticides. Alternative control strategies, such as biopesticides based on the Bacillus thuringiensis (Bt) toxins or transgenic plants expressing Bt toxins, can be used and are increasingly being adopted. Studies on the insect susceptibilities and modes of action of the different Bt toxins are crucial to determine management strategies to control the pests and to delay outbreaks of insect resistance. In the present study, the susceptibilities of both soybean pests to the Bt toxins Cry1Ac, Cry1Fa, Cry1Ca, and Cry2Aa have been investigated. Bioassays performed in first-instar larvae showed that both insects are susceptible to all these toxins. Competition-binding studies carried out with Cry1Ac and Cry1Fa 125-iodine labeled proteins demonstrated the presence of specific binding sites for both of them on the midgut brush border membrane vesicles (BBMVs) of both A. gemmatalis and C. includens Competition-binding experiments and specific-binding inhibition studies performed with selected sugars and lectins indicated that Cry1Ac and Cry1Fa share some, but not all, binding sites in the midguts of both insects. Also, the Cry1Ac- or Cry1Fa-binding sites were not shared with Cry1Ca or Cry2Aa in either soybean pest. This study contributes to the knowledge of Bt toxicity and midgut toxin binding sites in A. gemmatalis and C. includens and sheds light on the cross-resistance potential of Cry1Ac, Cry1Fa, Cry1Ca, and Cry2Aa Bt proteins as candidate proteins for Bt-pyramided crops.IMPORTANCE In the present study, the toxicity and the mode of action of the Bacillus thuringiensis (Bt) toxins Cry1Ac, Cry1Fa, Cry1Ca, and Cry2Aa in Anticarsia gemmatalis and Chrysodeixis includens (important defoliating pests of soybeans) have been investigated. These studies are crucial for determining management strategies for pest control. Bioassays showed that both insects were susceptible to the toxins. Competition-binding studies demonstrated the presence of Cry1Fa- and Cry1Ac-specific binding sites in the midguts of both pests. These results, together with the results from binding inhibition studies performed with sugars and lectins, indicated that Cry1Ac and Cry1Fa share some, but not all, binding sites, and that they were not shared with Cry1Ca or Cry2Aa in either soybean pest. This study contributes to the knowledge of Bt toxicity in A. gemmatalis and C. includens and sheds light on the cross-resistance potential of Cry1Ac, Cry1Fa, Cry1Ca, and Cry2Aa Bt proteins as candidate proteins for Bt-pyramided crops.

ABCC transporters mediate insect resistance to multiple Bt toxins revealed by bulk segregant analysis

BACKGROUND

Relatively recent evidence indicates that ABCC2 transporters play a main role in the mode of action of Bacillus thuringiensis (Bt) Cry1A-type proteins. Mapping of major Cry1A resistance genes has linked resistance to the ABCC2 locus in Heliothis virescens, Plutella xylostella, Trichoplusia ni and Bombyx mori, and mutations in this gene have been found in three of these Bt-resistant strains.

RESULTS

We have used a colony of Spodoptera exigua (Xen-R) highly resistant to a Bt commercial bioinsecticide to identify regions in the S. exigua genome containing loci for major resistance genes by using bulk segregant analysis (BSA). Results reveal a region containing three genes from the ABCC family (ABBC1, ABBC2 and ABBC3) and a mutation in one of them (ABBC2) as responsible for the resistance of S. exigua to the Bt commercial product and to its key Spodoptera-active ingredients, Cry1Ca. In contrast to all previously described mutations in ABCC2 genes that directly or indirectly affect the extracellular domains of the membrane protein, the ABCC2 mutation found in S. exigua affects an intracellular domain involved in ATP binding. Functional analyses of ABBC2 and ABBC3 support the role of both proteins in the mode of action of Bt toxins in S. exigua. Partial silencing of these genes with dsRNA decreased the susceptibility of wild type larvae to both Cry1Ac and Cry1Ca. In addition, reduction of ABBC2 and ABBC3 expression negatively affected some fitness components and induced up-regulation of arylphorin and repat5, genes that respond to Bt intoxication and that are found constitutively up-regulated in the Xen-R strain.

CONCLUSIONS

The current results show the involvement of different members of the ABCC family in the mode of action of B. thuringiensis proteins and expand the role of the ABCC2 transporter in B. thuringiensis resistance beyond the Cry1A family of proteins to include Cry1Ca.

Electrical hypothesis of toxicity of the Cry toxins for mosquito larvae

Many electrical properties of insect larval guts have been studied, but their importance for toxicity of the Cry-type toxins has never been reported in the literature. In the present work, we observed potential-dependent permeabilization of plasma membrane by several polycationic peptides derived from the Cry11Bb protoxin. The peptide BTM-P1d, all D-type amino acid analogue of the earlier reported peptide BTM-P1, demonstrated high membrane-permeabilizing activity in experiments with isolated rat liver mitochondria, RBC (red blood cells) and mitochondria in homogenates of Aedes aegypti larval guts. Two larger peptides, BTM-P2 and BTM-P3, as well as the Cry11Bb protoxin treated with the protease extract of mosquito larval guts showed similar effects. Only protease-resistant BTM-P1d, in comparison with other peptides, displayed A. aegypti larval toxicity. Taking into account the potential-dependent mechanism of membrane permeabilization by studied fragments of the Cry11Bb protoxin and the literature data related to the distribution of membrane and transepithelial potentials in the A. aegypti larval midgut, we suggest an electrical hypothesis of toxicity of the Cry toxins for mosquito larvae. According to this hypothesis, the electrical field distribution is one of the factors determining the midgut region most susceptible for insertion of activated toxins into the plasma membrane to form pores. In addition, potential-dependent penetration of short active toxin fragments into the epithelial cells could induce permeabilization of mitochondria and subsequent apoptosis or necrosis.

Association of Cry1Ac toxin resistance in Helicoverpa zea (Boddie) with increased alkaline phosphatase levels in the midgut lumen

Resistance to Bacillus thuringiensis Cry1Ac toxin was characterized in a population of Helicoverpa zea larvae previously shown not to have an alteration in toxin binding as the primary resistance mechanism to this toxin. Cry1Ac-selected larvae (AR1) were resistant to protoxins and toxins of Cry1Ab, Cry1Ac, and the corresponding modified proteins lacking helix α-1 (Cry1AbMod and Cry1AcMod). When comparing brush border membrane vesicles (BBMVs) prepared from susceptible (LC) and AR1 larval midguts, there were only negligible differences in overall Cry1Ac toxin binding, though AR1 had 18% reversible binding, in contrast to LC, in which all binding was irreversible. However, no differences were detected in Cry1Ac-induced pore formation activity in BBMVs from both strains. Enzymatic activities of two putative Cry1Ac receptors (aminopeptidase N [APN] and alkaline phosphatase [ALP]) were significantly reduced (2-fold and 3-fold, respectively) in BBMVs from AR1 compared to LC larvae. These reductions corresponded to reduced protein levels in midgut luminal contents only in the case of ALP, with an almost 10-fold increase in specific ALP activity in midgut fluids from AR1 compared to LC larvae. Partially purified H. zea ALP bound Cry1Ac toxin in ligand blots and competed with Cry1Ac toxin for BBMV binding. Based on these results, we suggest the existence of at least one mechanism of resistance to Cry1A toxins in H. zea involving binding of Cry1Ac toxin to an ALP receptor in the larval midgut lumen of resistant larvae.

Specific binding of activated Vip3Aa10 to Helicoverpa armigera brush border membrane vesicles results in pore formation

Helicoverpa armigera is one of the most harmful pests in China. Although it had been successfully controlled by Cry1A toxins, some H. armigera populations are building up resistance to Cry1A toxins in the laboratory. Vip3A, secreted by Bacillus thuringiensis, is another potential toxin against H. armigera. Previous reports showed that activated Vip3A performs its function by inserting into the midgut brush border membrane vesicles (BBMV) of susceptible insects. To further investigate the binding of Vip3A to BBMV of H. armigera, the full-length Vip3Aa10 toxin expressed in Escherichia coli was digested by trypsin or midgut juice extract, respectively. Among the fragments of digested Vip3Aa10, only a 62kDa fragment (Vip3Aa10-T) exhibited binding to BBMV of H. armigera and has insecticidal activity. Moreover, this interaction was specific and was not affected by the presence of Cry1Ab toxin. Binding of Vip3Aa10-T to BBMV resulted in the formation of an ion channel. Unlike Cry1A toxins, Vip3Aa10-T was just slightly associated with lipid rafts of BBMV. These data suggest that although activated Vip3Aa10 specifically interacts with BBMV of H. armigera and forms an ion channel, the mode of action of it may be different from that of Cry1A toxins.

Insecticidal properties of Sclerotinia sclerotiorum agglutinin and its interaction with insect tissues and cells

This project studied in detail the insecticidal activity of a fungal lectin from the sclerotes of Sclerotinia sclerotiorum, referred to as S. sclerotiorum agglutinin or SSA. Feeding assays with the pea aphid (Acyrthosiphon pisum) on an artificial diet containing different concentrations of SSA demonstrated a high mortality caused by this fungal lectin with a median insect toxicity value (LC50) of 66 (49-88) μg/ml. In an attempt to unravel the mode of action of SSA the binding and interaction of the lectin with insect tissues and cells were investigated. Histofluorescence studies on sections from aphids fed on an artificial liquid diet containing FITC-labeled SSA, indicated the insect midgut with its brush border zone as the primary target for SSA. In addition, exposure of insect midgut CF-203 cells to 25 μg/ml SSA resulted in a total loss of cell viability, the median cell toxicity value (EC50) being 4.0 (2.4-6.7) μg/ml. Interestingly, cell death was accompanied with DNA fragmentation, but the effect was caspase-3 independent. Analyses using fluorescence confocal microscopy demonstrated that FITC-labeled SSA was not internalized in the insect midgut cells, but bound to the cell surface. Prior incubation of the cells with saponin to achieve a higher cell membrane permeation resulted in an increased internalization of SSA in the insect midgut cells, but no increase in cell toxicity. Furthermore, since the toxicity of SSA for CF-203 cells was significantly reduced when SSA was incubated with GalNAc and asialomucin prior to treatment of the cells, the data of this project provide strong evidence that SSA binds with specific carbohydrate moieties on the cell membrane proteins to start a signaling transduction cascade leading to death of the midgut epithelial cells, which in turn results in insect mortality. The potential use of SSA in insect control is discussed.

Constitutive activation of the midgut response to Bacillus thuringiensis in Bt-resistant Spodoptera exigua

Bacillus thuringiensis is the most effective microbial control agent for controlling numerous species from different insect orders. The main threat for the long term use of B. thuringiensis in pest control is the ability of insects to develop resistance. Thus, the identification of insect genes involved in conferring resistance is of paramount importance. A colony of Spodoptera exigua (Lepidoptera: Noctuidae) was selected for 15 years in the laboratory for resistance to Xentari™, a B. thuringiensis-based insecticide, reaching a final resistance level of greater than 1,000-fold. Around 600 midgut ESTs were analyzed by DNA-macroarray in order to find differences in midgut gene expression between susceptible and resistant insects. Among the differentially expressed genes, repat and arylphorin were identified and their increased expression was correlated with B. thuringiensis resistance. We also found overlap among genes that were constitutively over-expressed in resistant insects with genes that were up-regulated in susceptible insects after exposure to Xentari™, suggesting a permanent activation of the response to Xentari™ in resistant insects. Increased aminopeptidase activity in the lumen of resistant insects in the absence of exposure to Xentari™ corroborated the hypothesis of permanent activation of response genes. Increase in midgut proliferation has been proposed as a mechanism of response to pathogens in the adult from several insect species. Analysis of S. exigua larvae revealed that midgut proliferation was neither increased in resistant insects nor induced by exposure of susceptible larvae to Xentari™, suggesting that mechanisms other than midgut proliferation are involved in the response to B. thuringiensis by S. exigua larvae.

Characterization of a Cry1Ac toxin-binding alkaline phosphatase in the midgut from Helicoverpa armigera (Hübner) larvae

Midgut membrane-bound alkaline phosphatases (mALP) tethered to the brush border membrane surface by a glycosylphosphatidylinositol (GPI) anchor have been proposed as crucial for Cry1Ac intoxication. In the present work, two full-length cDNAs-encoding alkaline phosphatases in the midgut of Helicoverpa armigera larvae were cloned and named HaALP1 (GenBank accession no. EU729322) and HaALP2 (GenBank accession no. EU729323), respectively. These two clones displayed high identity (above 94%) at the amino acid sequence, indicating that they may represent allelic variants, and were predicted to contain a GPI anchor. Protein sequence alignment revealed that HaALPs were grouped with mALP from the Heliothis virescens midgut. The HaALP1 and HaALP2 ( approximately 68kDa) proteins were heterologously expressed in Sf9 cells using a baculovirus expression system and purified to homogeneity. Ligand blot and dot blot analysis revealed that the Cry1Ac bound to both denatured and native purified HaALPs. Data from lectin blots, competition assays with soybean agglutinin (SBA) lectin and GalNAc binding inhibition assays were indicative of the presence of GalNAc on HaALPs and binding of Cry1Ac toxin to this residue. This observation was further confirmed through N-glycosidase digestion of HaALPs, which resulted in reduced Cry1Ac binding. Our data represent the first report on HaALPs and their putative role as receptors for Cry1Ac toxin in H. armigera.

Regulation of midgut growth, development, and metamorphosis

The insect midgut is an important site of entry for pathogens and insect control agents. This review focuses on recent information related to midgut epithelial growth, metamorphosis, and repair as a defense against pathogens. The roles of stem cell mitogens and differentiation factors are described. Included is a discussion of apoptosis and autophagy in the yellow body. Sloughing, also described, protects the midgut from virus infections and bacterial toxins through death and replacement of affected cells. The mechanisms by which the repair process reduces the effectiveness of pest control strategies are discussed. Primary tissue culture methods also are described, and their value in understanding the mechanisms by which biologically based insecticides work is discussed.

Cloning and characterization of the Cry1Ac-binding alkaline phosphatase (HvALP) from Heliothis virescens

Membrane-bound alkaline phosphatases (mALPs, EC 3.1.3.1) in the insect midgut have been reported as functional receptors for Cry toxins from the bacterium Bacillus thuringiensis. We previously reported the identification of HvALP in the midgut of Heliothis virescens larvae as a Cry1Ac-binding protein that is down-regulated in Cry1Ac-resistant insects. To further characterize HvALP, we localized mALP protein to foregut and midgut tissues using anti-mALP serum and then cloned five mALPs from H. virescens larval midgut. All five clones displayed high levels of sequence identity (above 90%), suggesting that they may represent allelic variants, and grouped with other lepidopteran mALPs in sequence alignments. All these cloned ALPs were predicted to contain a glycosylphosphatidylinositol (GPI) anchor and were named HvmALP1-5. We expressed two of the most diverse HvmALPs in a heterologous system to test binding of Cry1Ac and recognition by HvALP cross-reacting antiserum. Our data highlight the importance of glycosylation for Cry1Ac binding to HvALP and suggest that, depending on glycosylation, all the identified HvmALPs may be synonymous with HvALP, the Cry1Ac-binding phosphatase identified in H. virescens midgut epithelium.

Diversity of aminopeptidases, derived from four lepidopteran gene duplications, and polycalins expressed in the midgut of Helicoverpa armigera: identification of proteins binding the delta-endotoxin, Cry1Ac of Bacillus thuringiensis

Helicoverpa armigera midgut proteins that bind the Bacillus thuringiensis (Bt) delta-endotoxin Cry1Ac were purified by affinity chromatography. SDS-PAGE showed that several proteins were eluted with N-acetylgalactosamine and no further proteins were detected after elution with urea. Tandem mass spectral data for tryptic peptides initially indicated that the proteins resembled aminopeptidases (APNs) from other lepidopterans and cDNA sequences for seven APNs were isolated from H. armigera through a combination of cloning with primers derived from predicted peptide sequences and established EST libraries. Phylogenetic analysis showed lepidopteran APN genes in nine clades of which five were part of a lepidopteran-specific radiation. The Cry1Ac-binding proteins were then identified with four of the seven HaAPN genes. Three of those four APNs are likely orthologs of APNs characterised as Cry1Ac-binding proteins in other lepidopterans. The fourth Cry1Ac-binding APN has orthologs not previously identified as Cry1Ac-binding partners. The HaAPN genes were expressed predominantly in the midgut through larval development. Each showed consistent expression along the length of the midgut but five of the genes were expressed at levels about two orders of magnitude greater than the remaining two. The remaining mass spectral data identified sequences encoding polycalin proteins with multiple lipocalin-like domains. A polycalin has only been previously reported in another lepidopteran, Bombyx mori, but polycalins in both species are now linked with binding of Bt Cry toxins. This is the first report of hybrid, lipocalin-like domains in shorter polycalin sequences that are not present in the longest sequence. We propose that these hybrid domains are generated by alternative splicing of the mRNA.