Expression and immunolocalisation of odorant-binding and chemosensory proteins in locusts

We have identified, cloned and expressed a new chemosensory protein (CSP) in the desert locust Schistocerca gregaria belonging to a third sub-class of these polypeptides. Polyclonal antibodies stained a band of 14 kDa, as expected, in the extracts of antennae and palps of the adults, but not in the 4th and 5th instars. In the related species Locusta migratoria, instead, the same antibodies cross-reacted only with a band of apparent molecular mass of 35 kDa in the extract of 1st-5th instars, but not in the adults. The recombinant protein binds the fluorescent probe N-phenyl-1-naphthylamine, but none of the compounds so far reported as pheromones for S. gregaria. The expression of the odorant-binding protein (OBP) and of CSPs of sub-classes I and II was also monitored in antennae, tarsi, palpi, wings and other organs of solitary and gregarious locusts in their nymphal and adult stages. OBP was found to be antenna specific, where it is expressed at least from the 3rd instar in both solitary and gregarious locusts. CSPs, instead, appear to be more ubiquitous, with different expression patterns, according to the sub-class. Immunocytochemistry experiments revealed that OBP is present in the sensillum lymph of sensilla trichodea and basiconica, while CSP-I and CSP-III were found in the outer sensillum lymph of sensilla chaetica and in the sub-cuticular space between epidermis and cuticle of the antenna. Sensilla chaetica on other parts of the body showed the same expression of CSP-I as those on the antenna.

Expression of odorant-binding proteins and chemosensory proteins in some Hymenoptera

The expression of chemosensory proteins (CSPs) and odorant-binding proteins (OBPs) in individuals of different castes and ages have been monitored in three species of social hymenopterans, Polistes dominulus (Hymenoptera, Vespidae), Vespa crabro (Hymenoptera, Vespidae) and Apis mellifera (Hymenoptera, Apidae), using PCR with specific primers and polyclonal antibodies. In the paper wasp P. dominulus, OBP is equally expressed in antennae, wings and legs of all castes and ages, while CSP is often specifically present in antennae and in some cases also in legs. In the vespine species V. crabro CSP is antennal specific, while OBP is also expressed in legs and wings. The three CSPs and the five OBPs of A. mellifera show a complex pattern of expression, where both classes of proteins include members specifically expressed in antennae and others present in other parts of the body. These data indicate that at least in some hymenopteran species CSPs are specifically expressed in antennae and could perform roles in chemosensory perception so far assigned only to OBPs.

Soluble proteins of chemical communication in the social wasp Polistes dominulus

Members of the odorant-binding protein (OBP) and chemosensory protein (CSP) families were identified and characterised in the sensory tissues of the social wasp Polistes dominulus (Hymenoptera: Vespidae). Unlike most insects so far investigated, OBPs were detected in antennae, legs and wings, while CSPs appeared to be preferentially expressed in the antennae. The OBP is very different from the homologous proteins of other Hymenopteran species, with around 20% of identical residues, while the CSP appears to be much better conserved. Both OBP and CSP, not showing other post-translational modifications apart from disulphide bridges, were expressed with high yields in a bacterial system. Cysteine pairing in the recombinant and native proteins follows the classical arrangements described for other members of these classes of proteins. OBPs isolated from the wings were found to be associated with a number of long-chain aliphatic amides and other small organic molecules. Binding of these ligands and other related compounds was measured for both recombinant OBP and CSP.

Chemosensory proteins of Locusta migratoria

Two different classes of chemosensory proteins (CSPs) in Locusta migratoria have been identified on the basis of the molecular cloning of a series of different cDNAs from the antennae of this insect. Several CSP isoforms have been purified and biochemically characterized from antennal and wing extracts, some of them corresponding to expression products predicted for the identified cDNAs. In wings, the nature of the main endogenous ligand binding to these proteins was determined as oleoamide by a gas chromatography-mass spectrometric approach. One of these isoforms has been expressed in a bacterial system with high yield and used in a fluorescent binding assay. Competitive binding experiments have indicated the presence of long-chain compounds among the best ligands.

Bacterial expression and conformational analysis of a chemosensory protein from Schistocerca gregaria

Chemosensory proteins (CSPs) are a class of small, soluble proteins present at high concentrations in chemosensory organs of different insect species. Several pieces of evidence suggest their involvement in carrying chemical messages from the environment to chemosensory receptors. However, a structural description of the mechanism of delivery has not been reported. In order to provide the first detailed conformational characterization of these molecules, we cloned a specific isoform (CSP-sg4) from Schistocerca gregaria and expressed it in Escherichia coli. The product was obtained with yields of more than 20 mg per L of culture, all in its soluble form. The recombinant protein was identical to the native one with respect to pairing of the disulfide bridges, aggregative state and secondary structure elements. Structural investigations revealed a significantly stable polypeptide with respect to variations in temperature and acidity. CD analysis, preliminary NMR data and secondary structure prediction pointed to a correctly folded structure where helical regions and loops are alternated in a similar fashion as that observed for other classes of odorant- and pheromone-binding proteins presenting no sequence similarity to CSPs.

Purification, cloning and characterisation of odorant- and pheromone-binding proteins from pig nasal epithelium

Two distinct classes of lipocalin isoforms (OBP-IIs and OBP-IIIs) were purified and identified from porcine nasal mucosa of male and female individuals. Using primers designed on their N-terminal sequence, the complete primary structures of the mature polypeptides were determined. Mass spectrometry analysis confirmed the identity of the cDNA-derived sequences and provided information regarding their post-translational modifications. These species strongly resemble a lipocalin expressed by von Ebner's gland and salivary lipocalins carrying sex-specific pheromones secreted only by the boar's submaxillary glands. Both OBP-IIs and OBP-IIIs present two cysteines paired in a disulphide bond; the remaining residues occur in a reduced form. In addition, OBP-IIIs are heavily glycosylated and markedly different in their glycan moiety from the salivary lipocalins. A three-dimensional model is proposed based on protein species with known structure. Like salivary lipocalins, OBP-IIIs bind a number of odorant molecules, with highest affinity for the specific pheromone 5alpha-androst-16-en-3-one. The high similarity between OBPs from the nasal area and lipocalins from secretory glands suggests a common function in binding the same pheromonal ligands, the latter carrying chemical messages into the environment the former delivering them to specific receptors.

Soluble proteins from chemosensory organs of Eurycantha calcarata (Insects, Phasmatodea)

Three related nucleotide sequences, encoding mature proteins of 108-113 amino acids, have been obtained from antennal cDNA of the Phasmid Eurycantha calcarata. Among these, one is also expressed in the tarsi as demonstrated by N-terminal sequence and mass spectrometric analyses of protein samples isolated from both organs. PCR experiments performed with specific primers, showed that this species is also expressed in the mouth organs and in the cuticle, while the other two are antennal specific. All three isoforms are similar to Drosophila OS-D and other proteins reported in several insect orders, but one of them is significantly different from the other two. The best conserved elements are the N-terminal region and the four cysteine residues. Accurate ESMS measurements indicated that all cysteines are involved in two disulphide bonds and ruled out the occurrence of additional post-translational modifications. Polyclonal antibodies, raised against the purified protein, did not react with proteins of the same class expressed in another Phasmid species, Carausius morosus, and in the orthopteran Schistocerca gregaria, nor did antibodies against these proteins recognise those of E. calcarata.

Production of a soluble and functional recombinant streptavidin in Escherichia coli

The cDNA for streptavidin (residues 15-159) was subcloned into an expression vector in fusion at the N-terminus with the T7-tag (12 residues). Conditions were found to express the protein in Escherichia coli in a soluble, assembled, and active form. The protein was purified in two simple steps which involved heating at 75 degreesC and affinity chromatography on iminobiotin agarose. The purified protein was obtained in yields of 70 mg per liter of bacterial culture. Electron spray mass spectrometry analysis showed that the recombinant streptavidin had the expected molecular mass without covalent modifications. ELISA and surface plasmon resonance analyses showed it to be functionally analogous to the natural streptavidin. This appears to be an improvement over the reported methods of recombinant streptavidin production which involve protein renaturation or the use of eukaryotic expression systems.

Biochemical and immunological characterization of recombinant allergen Lol p 1

Pollen from perennial rye grass (Lolium perenne), a major cause of type-I allergy worldwide, contains a complex mixture of allergenic proteins among which Lol p 1 is one of the most important. We describe the expression, purification and characterization of a recombinant Lol p 1 overproduced in Escherichia coli. The recombinant allergen, expressed in high yields and purified in milligram amounts, bound to specific IgE antibodies from human sera, induced histamine release from sensitized human basophils, and elicited rabbit antisera that recognize specifically recombinant Lol p 1 and natural Lol p 1 of pollen extract. Recombinant Lol p 1 was used to develop ImmunoCAP assays for analysis of 150 sera that were Radioallergosorbent test positive to L. perenne pollen. In 130 of them (87%) the assay detected a significant level of IgE antibodies to Lol p 1, reaching on average 37% of the level obtained with a test for IgE to the whole grass pollen extract. To map epitopes on Lol p 1, we produced three deletion mutants [des-(116-240)-Lol p 1, des-(1-88)-Lol p 1 and des-(133-189)-Lol p 1], which were efficiently expressed in bacteria. These all showed a strong reactivity with the specific rabbit IgG antibodies, but lacked most or all the allergenic properties of recombinant Lol p 1. A study of the antigenic structure of Lol p 1 was performed using the three deletion mutants and a set of 17-18-residue overlapping synthetic peptides covering the whole allergen sequence. The results indicate that human IgE and rabbit IgG antibodies bind to distinct regions of Lol p 1, and that at least some important IgE epitopes are mainly conformational. The findings suggest that recombinant allergens constitute useful reagents for further development of serological diagnosis of allergy, and that it should be possible to produce immunogenic fragments of allergenic proteins without allergenic properties.

Production and structure characterisation of recombinant chromogranin A N-terminal fragments (vasostatins) -- evidence of dimer-monomer equilibria

Vasostatins (VS) are vasoinhibitory peptides derived from the N-terminal domain of chromogranin A, a secretory protein present in the electron-dense granules of many neuroendocrine cells. In this work we describe a method for the production in Escherichia coli of large amounts of recombinant vasostatins, corresponding to chromogranin A residues 1-78 (VS-1), and 1-115 (VS-2), and the use of these materials for structure characterisation. The masses of both products were close to the expected values, by SDS/PAGE and mass spectrometry analysis. However, their hydrodynamic behaviours in size-exclusion chromatography corresponded to that of proteins with a larger size. SDS/PAGE analysis of VS-1 and VS-2 after cross-linking with disuccinimidyl suberate indicated that both polypeptides form dimers. VS-2 was almost entirely dimeric at > 4 microM, but rapidly converted to monomer after dilution to 70 nM. The rapid dimer-monomer transition of VS-2 after dilution could be part of a mechanism for regulating its activity and localising its action. Immunological studies of VS-1 have shown that residues 37-70 constitute a highly antigenic region characterised by an abundance of linear epitopes efficiently mimicked by synthetic peptides. The recombinant products and the immunological reagents developed in this work could be valuable tools for further investigating the structure and the function of chromogranin A and its fragments.

Phosphorylation of human pro-urokinase on Ser138/303 impairs its receptor-dependent ability to promote myelomonocytic adherence and motility

Serine phosphorylation of human pro-urokinase (pro-uPA) by A431 human carcinoma cells results in a catalytically active molecule with reduced sensitivity to plasminogen activator inhibitor type 1. We mapped the phosphorylated seryl residues by analyzing the in vivo phosphorylation state of engineered pro-uPA variants carrying a COOH-terminal poly-histidine tag. Stably transfected A431 cells do not incorporate radioactive phosphate into tagged pro-uPA in which the serines 138 and 303 have been replaced with glutamic residues, although endogenous nontagged pro-uPA is 32P-labeled on A and B chains. Moreover, the catalytic-independent ability of the mono- and di-substituted "phosphorylation-like" variants to bind to the GPI-anchored urokinase receptor (uPAR) and promote adherence of differentiating U937, HL-60, and THP-1 myelomonocytic cells was examined. We found that glutamic residues as well as the naturally occurring phosphoserines at positions 138 and 303 abolish proadhesive ability, although they do not interfere with receptor binding. In addition, pro-uPA carrying Glu138/303 lacks the capability to induce a chemotactic response of THP-1 cells. The exclusive presence of Glu138 reduces pro-uPA proadhesive and chemotactic ability by 70-80%, indicating that a phosphoserine residue at the same position plays a major inhibitory role of myeloid cell response to pro-urokinase. The di-substitution does not affect pro-uPA ability to interact with vitronectin or to enhance binding of urea-denatured vitronectin to uPAR. However, unlike wild-type tagged pro-uPA, the di-substituted variant does not induce receptor polarization in pre-adherent U937 cells. Taken together, the data support the possibility that pro-uPA phosphorylation on Ser138/303 can modulate uPAR transducing ability.

Characterisation of circulating chromogranin A in human cancer patients

The structure of circulating chromogranin A (CgA) of phaeochromocytoma patients was characterised and compared with that of CgA extracted from tumours. Size exclusion chromatography experiments provided evidence that CgA is present in the blood of different patients, as well as in tumour extracts, as multiple forms having different hydrodynamic sizes of 600 kDa (CgA-I), 100 kDa (CgA-II) and 55 kDA (CgA-III). The amount of each CgA form as a proportion of the total antigenic material was different in different patients. Western blot analysis of chromatographic fractions indicated that these forms are made up by polypeptides of similar molecular weight (about 60-70 kDa). All CgA forms express the epitopes recognised by two monoclonal antibodies (A11 and B4E11), directed against residues 68-70 and 81-90 of human CgA. However, their relative immunoreactivity was markedly different. No evidence for the presence of multimeric complexes in the CgA-I fraction was obtained by various immunological and biochemical methods. These results suggest that circulating CgA in phaeochromocytoma patients consists of at least three forms that appear to be made up by polypeptides with similar molecular weight and different hydrodynamic properties and immunoreactivity. We hypothesise that different conformations and shapes contribute to the heterogeneity of circulating CgA.

Recombinant allergen Lol p II: expression, purification and characterization

Pollen from perennial rye grass (Lolium perenne) is a major cause of type I allergies worldwide. It contains complex mixtures of proteins, among which Lol p II is a major allergen. Previously, we have reported the cloning and sequencing of Lol p II and its expression in fusion with the heavy chain of human ferritin as carrier polypeptide (Sidoli et al., 1993, J. biol. Chem. 268, 21819-21825). Here, we describe the expression, purification and characterization of a recombinant Lol p II overproduced as a non-fusion protein in the periplasm of E. coli. The recombinant allergen was expressed in high yields and was easily purified in milligram amounts. It competed with the natural Lol p II for binding to specific IgE, and it induced allergic responses in skin prick tests, indicating to be immunologically analogous to the natural protein. Biochemical analyses indicate that recombinant Lol p II is a highly stable and soluble monomeric molecule which behaves like a small globular protein.

Use of the urokinase-type plasminogen activator gene as a general tool to monitor expression in transgenic animals: study of the tissue-specificity of the murine whey acidic protein (WAP) expression signals

Urokinase-type plasminogen activator (uPA) is a proteolytic enzyme able to convert the zymogen plasminogen into the strong protease plasmin. The availability of very sensitive tests to measure the enzymatic activity of a plasminogen activator renders the corresponding gene an ideal candidate for the detection of promoter activity. In this paper we describe the utilization of the human uPA gene as detector of tissue-specificity of the murine whey acidic protein (WAP) expression signals in transgenic mice. The WAP promoter has been previously investigated for the production of foreign proteins in the milk of transgenic animals. In our genetic constructions, the human uPA cDNA was linked to the promoter region as well as to 3'-end distal sequences of the WAP gene. Five transgenic lines were obtained in which, however, expression levels of human uPA in the milk were still quite low. Surprisingly, four of these five positive transgenic mice show a consistent activity of the WAP promoter in brain extracts compared to other tissues.

Efficient renaturation and fibrinolytic properties of prourokinase and a deletion mutant expressed in Escherichia coli as inclusion bodies

Prourokinase is a plasminogen activator of 411 amino acids which displays a clot-lysis activity through a fibrin-dependent mechanism, and which seems to be a promising agent for the treatment of acute myocardial infarction. The preparation of recombinant prourokinase in bacteria has been hampered by its insolubility and by difficulty in refolding the polypeptide chain. In this paper we describe the renaturation process of two recombinant proteins expressed in Escherichia coli as inclusion bodies: prourokinase and a deletion derivative (delta 125-prourokinase) in which 125 amino acids of the N-terminal region have been removed. Deletion of this sequence brings to higher refolding yields and faster kinetics (first-order rate constant of renaturation of 0.57 h-1 for delta 125-prourokinase and 0.25 h-1 for prourokinase). Our process involves sequential steps of denaturation, reduction and controlled refolding of the polypeptide chain. When applied to pure, non-glycosylated and active prourokinase, it gives a refolding yield of about 80%, demonstrating the efficiency of the renaturation procedure. Lower yields (15% and 30%, respectively, for prourokinase and delta 125-prourokinase) were obtained when the same refolding protocol was applied to inclusion bodies from bacteria. After purification to homogeneity (as shown by HPLC and SDS/PAGE) specific activities were 160,000 and 250,000 IU/mg protein, respectively, for prourokinase and delta 125-prourokinase. As with prourokinase, the deletion mutant delta 125-prourokinase displays a zymogenic nature, being activated by plasmin to the active two-chain form; however, this mutant is approximately fourfold more resistant than prourokinase to plasmin activation, and consequently shows a different fibrinolytic profile.

Identification of the yeast DNA polymerase I gene with antibody probes

Partially overlapping fragments of the gene encoding yeast DNA polymerase I have been cloned by immunological screening of a yeast genomic library constructed in the phage lambda expression vector lambda gt11. The three gene fragments we analyzed in detail encode part of a yeast protein that has been identified as yeast DNA polymerase I, because it shares with this enzyme a number of antigenic determinants. In fact, the yeast protein fragments expressed by the recombinant phages react with both polyclonal and monoclonal antibodies raised against different, highly purified preparations of DNA polymerase I. Moreover, they can be used to affinity purify antibodies specifically reacting with active DNA polymerase I polypeptides and they compete with the yeast enzyme for binding to antibodies that inhibit catalytic activity. The gene is located on chromosome XIV in the yeast genome, and it is transcribed as a 5.2 kb mRNA.