Insect immunity. Purification and properties of three inducible bactericidal proteins from hemolymph of immunized pupae of Hyalophora cecropia

Purification of an insect defensin from the mosquito, Aedes aegypti

Using a new, sensitive assay of bacterial growth inhibition, inducible antibacterial activity has been identified in the haemolymph of the mosquito, Aedes aegypti following inoculation with bacteria or with microfilariae of the filarial nematode Brugia pahangi, but not after inoculation with sterile culture medium. A lower level of antibacterial activity has also been observed in untreated individual mosquitoes. Following bacterial inoculation, a basic, inducible antibacterial peptide has been detected using native PAGE at pH 4, which corresponds with a 4.5 kDa peptide detected by tricine SDS-PAGE followed by silver staining. A peptide has been purified from immune haemolymph by ultrafiltration, followed by reversed-phase HPLC, yielding a single major peak with antibacterial activity. Partial amino acid sequence analysis of this fraction has revealed substantial homology with insect defensins. The data are consistent with the peptide being another member of this family, and we propose the name Aedes aegypti defensin.

Characterization of the antimicrobial peptide derived from sapecin B, an antibacterial protein of Sarcophaga peregrina (flesh fly)

Sapecin B, an antibacterial protein of Sarcophaga peregrina, was divided into four peptides. A hendecapeptide derived from its helix region was found to have comparable antibacterial activity with that of the complete protein. This peptide had a much wider spectrum of antimicrobial activity than that of sapecin B, exhibiting activity on not only Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative), but also some yeasts, including Candida albicans. The peptide was shown to bind to liposomes containing acidic phospholipids and cause release of entrapped glucose, suggesting that its primary site of action is the bacterial membrane. Its antimicrobial activity could be increased by substituting various amino acid residues for hydrophobic and/or basic ones.

The inducible antibacterial peptides of insects

Insects respond to bacterial challenge by the rapid and transient synthesis of a large number of potent antibacterial peptides that are active against many different bacteria. Two families of inducible antibacterial peptides are well characterized: the cecropins and the insect defensins. A rapidly increasing number of proline- and glycine-rich peptides are reported from various insect species together with cecropins and insect defensins. In this review, Stéphane Cociancich, Philippe Bulet, Charles Hetru and Jules A. Hoffmann give an update of our current information on the induced antibacterial peptides.

The lysozyme locus in Drosophila melanogaster: an expanded gene family adapted for expression in the digestive tract

Lysozyme has been studied in insects as part of the system of inducible antibacterial defence in the haemolymph. We recently found two Drosophila lysozyme genes that are constitutively expressed in the digestive tract, and are probably involved in the digestion of bacteria in the food. To obtain an overview of the lysozyme genes in this species and their possible roles in immunity and digestion, we have now characterized all six lysozyme genes in the cloned part of the lysozyme locus at 61F, and a seventh gene that maps to the same chromosomal location. The expression of the genes follows four different patterns: firstly, four closely related genes, LysB, C, D and E, are all strongly expressed in the midgut of larvae and adults; secondly, LysP is expressed in the adult salivary gland; thirdly, LysS is expressed mainly in the gastric caecae of larvae; and finally, LysX is primarily expressed in the metamorphosing midgut of late larvae and early pupae. The LysD-like genes and LysS are strongly repressed in artificially infected animals, possibly reflecting a malaise reaction in the digestive tract. None of the genes is expressed in the fat body or haemocytes. Thus rather than being a component of the haemolymph, the Drosophila lysozymes are found mainly in the digestive tract where they are expressed at a high level. Furthermore all genes, except LysP, encode acidic proteins, in contrast to the strongly basic "typical" lysozymes. This is highly reminiscent of the situation in ruminants, where the lysozymes have been recruited for the digestion of symbiotic bacteria in the stomach.

Induction of antibacterial protein synthesis by soluble peptidoglycan in isolated fat body from larvae of the silkworm, Bombyx mori

Synthesis and secretion of bactericidal protein (cecropin) and lysozyme were induced by soluble peptidoglycan fragments (SPG) from Escherichia coli in a culture of fat body from Bombyx mori larvae. The rate of the secretion by fat body increased as a function of SPG concentration added to the culture medium. The induction of bactericidal activity was specific for peptidoglycan of a particular structure. Thus, SPG from Micrococcus luteus was 500-times less potent than E. coli SPG, and various glucans and peptides structurally related to peptidoglycan were all ineffective as elicitor. These results support the hypothesis that bacteria invading the haemocoel have to be partially degraded to generate peptidoglycan fragments as a signal molecule, which subsequently acts on a receptor on fat body cells and induces antibacterial protein synthesis.

Recombinant DNA procedures for producing small antimicrobial cationic peptides in bacteria

Natural polycationic antibiotic peptides have been found in many different species of animals and insects and shown to have broad antimicrobial activity. To permit further studies on these peptides, bacterial expression systems were developed. Attempts to produce these peptides with an N-terminal signal sequence were unsuccessful due to the lability of the basic peptides. Therefore, a number of different fusion protein systems were tested, including fusions to glutathione-S-transferase (GST) (on plasmid pGEX-KP), Pseudomonas aeruginosa outer membrane protein OprF (on plasmid pRW5), Staphylococcus aureus protein A (on plasmid pRIT5), and the duplicated IgG-binding domains of protein A (on plasmid pEZZ18). In the first three cases, stable fusion proteins with the defensin, human neutrophil peptide 1 (HNP-1), and/or a synthetic cecropin/melittin hybrid (CEME) were obtained. In the course of these studies, we developed a novel method of purifying inclusion bodies, using the detergent octyl-polyoxyethylene (octyl-POE), as well as establishing methods for preventing fusion protein proteolytic breakdown. Cationic peptides could be successfully released from the carrier protein with high efficiency by chemical means (CNBr cleavage) and with low efficiency by enzymatic cleavage (using factor Xa protease). Fusions of protein A to cationic peptides were secreted into the culture supernatant of S. aureus clones and after affinity purification, CNBr digestion and column chromatography, pure cationic peptide was obtained. CEME produced by this procedure had the same amino acid (aa) content, aa sequence, gel electrophoretic mobility and antibacterial activity as CEME produced by protein chemical procedures.

Modification of the C terminus of cecropin is essential for broad-spectrum antimicrobial activity

Cecropin A is a naturally occurring peptide with bactericidal activity against gram-negative and gram-positive bacteria. Production of large quantities of bactericidal peptides that are similar in structure and activity to cecropin A has been achieved by combining recombinant DNA techniques and techniques and chemical modification. Expression of the bactericidal peptide in Escherichia coli was accomplished through the formation of a fusion protein. The 5' end of the L-ribulokinase gene was fused to a single copy of a synthetic gene encoding cecropin A. A methionine codon was engineered between the two genes, and a methionylglycine extension was introduced at the C terminus of cecropin A. Cyanogen bromide treatment of the fusion protein yielded cecropin A with a C-terminal homoserine. The recombinant cecropin A with a homoserine at the C terminus did not kill most gram-positive bacteria tested. However, recombinant cecropin A with a chemically modified C terminus has antimicrobial activity similar to that of cecropin produced by cecropia pupae.

Purification and primary structure of ceratotoxin A and B, two antibacterial peptides from the female reproductive accessory glands of the medfly Ceratitis capitata (Insecta:Diptera)

In the present article we report the purification and the amino acid sequence of two antibacterial peptides present in the secretion of the female reproductive accessory glands of the dipteran insect Ceratitis capitata. Both peptides consist of 29 amino acid residues, are heat stable, strongly basic and differ from each other for the substitution of two amino acids. Their primary sequence and predicted secondary structure are related to other families of peptides known to have lytic and/or antibacterial activity. We propose the name ceratotoxins (from Ceratitis) for these antibacterial peptides.

Mechanisms of action on Escherichia coli of cecropin P1 and PR-39, two antibacterial peptides from pig intestine

Cecropin P1 and PR-39 are two antibacterial peptides isolated from the upper part of the small intestine of the pig. They have been sequenced, and their antibacterial spectra have been investigated (J.-Y. Lee, A. Boman, C. Sun, M. Andersson, H. Jörnvall, V. Mutt, and H. G. Boman, Proc. Natl. Acad. Sci. USA 86:9159-9162, 1989; B. Agerberth, J.-Y. Lee, T. Bergman, M. Carlquist, H. G. Boman, V. Mutt, and H. Jörnvall, Eur. J. Biochem. 202:849-854, 1991). We have now compared these two peptides for their mechanism of action on Escherichia coli K-12 by using three strains with different markers. Our results show that cecropin P1, like other cecropins, kills bacteria by lysis and that this reaction requires more peptide to kill more cells. PR-39 requires a lag period of about 8 min to penetrate the outer membrane of wild-type E. coli; then killing is quite fast. This lag period was absent in the envA1 mutant; in this strain the outer membrane was freely permeable to both peptides. PR-39 killed growing bacteria faster than nongrowing cells; for cecropin P1 there was no such difference. It is suggested from isotope incorporation experiments that PR-39 kills bacteria by a mechanism that stops protein and DNA synthesis and results in degradation of these components.

Role of the integument in insect immunity: epicuticular abrasion and induction of cecropin synthesis in cuticular epithelial cells

When the epicuticle of a silkworm larva, Bombyx mori, was lightly abraded in the presence of live Bacillus licheniformis, Enterobacter cloacae, or bacterial cell wall components, cecropin mRNAs were detected in the underlying epithelial cells and in fat body cells remote from the abraded area. Antibacterial activity due to cecropin was detected in the matrix of the lightly abraded cuticle but not in nonabraded portions of the cuticular matrix or in the hemolymph surrounding the fat body, unless a more severe cuticular abrasion was administered. A light abrasion to a larva of the giant silkworm moth, Hyalophora cecropia, in the presence of E. cloacae also induced antibacterial activity in the abraded cuticle. These data illustrate that the ectodermally derived lepidopteran larval integument, when challenged by live bacteria or their cell wall components, mounts an immune response. Hence, the insect exoskeleton, which is often considered as an inert protective armor, is indeed actively participating in defense.

Efficient secretion of attacin from insect fat-body cells requires proper processing of the prosequence

The attacins constitute a group of immune proteins induced after bacterial infection in the moth Hyalophora cecropia. They are synthesized as preproproteins and undergo post-translational modification during transport to the hemolymph. The processing and transport rates of attacin were studied in its natural host as a response to infection. Monensin totally inhibited the processing from proattacin to attacin and the radiolabeled proattacin remained intracellular. This observation indicated that the prosequence is removed at or after the trans-Golgi compartment. It is also suggested that the processing of the prosequence does not occur in acidic vesicles, as the process was not inhibited by the weak base chloroquine. To study prosequence function, the attacin gene and genes with mutations in the prosequence were cloned into the baculovirus Autographa californica nuclear polyhedrosis virus. The processing of proattacin and the transport of attacin were studied by pulse-chase experiments with fat body isolated from Trichoplusia ni larvae. The rate of secretion from fat body was lowest for proattacin, which could not be processed to attacin, intermediate for attacins lacking the prosequence and highest for natural attacin. We could not detect any biological activity for proattacin.

Immune reactions in Drosophila and other insects: a model for innate immunity

All insects defend themselves against bacteria and parasites, using cellular and humoral systems that are rapidly activated in infected animals. Among the induced effector molecules are antibacterial proteins and peptides such as cecropins, attacins, lysozymes and insect defensins, the genes for many of which have now been cloned. The induction of this system, which lacks clonally selected receptors like those of vertebrate B and T cells, may provide a model for innate immune reactions in other animals, including vertebrates.

Identification of serum components that inhibit the tumoricidal activity of amphiphilic alpha helical peptides

Antimicrobial peptides that can form amphiphilic alpha helices were tested for their ability to lyse various human tumor cell lines in vitro. These peptides include C18G, whose sequence is a derivative of the carboxyl terminus of human platelet factor IV, and 399, an idealized amphiphilic alpha helix. Both peptides exhibited potent antitumor activity against all cell lines tested, unlike magainin 2, a naturally occurring antimicrobial peptide of similar structure, which was relatively inactive under the same conditions. Also, the lytic activity of C18G is specific for tumor cells versus human red blood cells. The effects of serum can be important when evaluating the potency of lytic peptides, since other tumoricidal peptides have been shown to be completely inactivated by low serum levels. Experiments with C18G and 399 revealed that their activity was indeed reduced in the presence of human serum, but that significant lytic activity remained even at relatively high serum concentrations. Various serum components were tested for their inhibitory activity. Whereas albumin and high-density lipoprotein had only slight inhibitory properties, low-density lipoprotein was found to be a potent inhibitor of peptide-mediated cell lysis. The peptide 399, which is more sensitive to serum inhibition than C18G, also binds more extensively to all serum components tested.

Morphological aspects of Achacin-treated bacteria

1. The morphology of bacteria treated with the bactericidal glycoprotein, Achacin, purified from the giant African snail, Achatina fulica Férussac, has been studied. 2. Achacin lengthens the bodies of Escherichia coli by three to seven times. 3. Achacin damages the surface of Staphylococcus aureus and sinks the cytoplasmic membranes into the cytoplasm. 4. Achacin causes neither the leakage nor the destruction of cells.

Modeling the ion channel structure of cecropin

Atomic-scale computer models were developed for how cecropin peptides may assemble in membranes to form two types of ion channels. The models are based on experimental data and physiochemical principles. Initially, cecropin peptides, in a helix-bend-helix motif, were arranged as antiparallel dimers to position conserved residues of adjacent monomers in contact. The dimers were postulated to bind to the membrane with the NH2-terminal helices sunken into the head-group layer and the COOH-terminal helices spanning the hydrophobic core. This causes a thinning of the top lipid layer of the membrane. A collection of the membrane bound dimers were then used to form the type I channel structure, with the pore formed by the transmembrane COOH-terminal helices. Type I channels were then assembled into a hexagonal lattice to explain the large number of peptides that bind to the bacterium. A concerted conformational change of a type I channel leads to the larger type II channel, in which the pore is formed by the NH2-terminal helices. By having the dimers move together, the NH2-terminal helices are inserted into the hydrophobic core without having to desolvate the charged residues. It is also shown how this could bring lipid head-groups into the pore lining.

Antibacterial peptides designed as analogs or hybrids of cecropins and melittin

Eight new analogs of cecropin A, two new analogs of melittin and 30 hybrid peptides containing sequences from cecropins and melittin have been synthesized. The lengths of the peptides have varied from 37 residues (the length of cecropin A) to 18 residues. The peptides have been assayed for lysis of sheep red blood cells and for antibacterial activity against two Gram negative and three Gram positive bacteria. The best analogs of cecropin A maintained the anti-Escherichia coli activity of the parental peptide, and were not lytic for red blood cells. Melittin and its replacement analogs were all lytic for red blood cells, but an analog with transposed segments was not. Several of the hybrid peptides were found to be both non-hemolytic and highly active against all test bacteria. The data were used to define the structural requirements for antibacterial activity.

Molecular cloning of the antibacterial protein of the giant African snail, Achatina fulica Férussac

An expression cDNA library was constructed with poly(A)-rich RNA extracted from the collar of the giant African snail, Achatina fulica Férussac. A 1.9-kbp cDNA clone encoding a precursor of antibacterial glycoprotein of the snail, achacin, was isolated from the cDNA expression library. The cDNA sequence contains an open reading frame with 1593-nucleotide residues. The deduced amino acid sequence of this achacin precursor starts with a 29-residue leader peptide followed by a 502-residue mature peptide (56 kDa) with four possible N-glycosylation sites, Asn-Xaa-Ser or Asn-Xaa-Thr. The Northern-blot analysis proved that the achacin precursor was specifically expressed in the tissue of snail collar and processed to mature achacin. cDNA inserts encoding achacin precursor were subcloned into expression plasmids. Three kinds of expressed polypeptides were cross-reacted with rabbit antiserum raised against achacin. The largest polypeptide (M(r) 63,000) should be the achacin precursor.

Agents that increase the permeability of the outer membrane

The outer membrane of gram-negative bacteria provides the cell with an effective permeability barrier against external noxious agents, including antibiotics, but is itself a target for antibacterial agents such as polycations and chelators. Both groups of agents weaken the molecular interactions of the lipopolysaccharide constituent of the outer membrane. Various polycations are able, at least under certain conditions, to bind to the anionic sites of lipopolysaccharide. Many of these disorganize and cross the outer membrane and render it permeable to drugs which permeate the intact membrane very poorly. These polycations include polymyxins and their derivatives, protamine, polymers of basic amino acids, compound 48/80, insect cecropins, reptilian magainins, various cationic leukocyte peptides (defensins, bactenecins, bactericidal/permeability-increasing protein, and others), aminoglycosides, and many more. However, the cationic character is not the sole determinant required for the permeabilizing activity, and therefore some of the agents are much more effective permeabilizers than others. They are useful tools in studies in which the poor permeability of the outer membrane poses problems. Some of them undoubtedly have a role as natural antibiotic substances, and they or their derivatives might have some potential as pharmaceutical agents in antibacterial therapy as well. Also, chelators (such as EDTA, nitrilotriacetic acid, and sodium hexametaphosphate), which disintegrate the outer membrane by removing Mg2+ and Ca2+, are effective and valuable permeabilizers.

Bactericidal action of a glycoprotein from the body surface mucus of giant African snail

1. Bactericidal action of a glycoprotein, Achacin, purified from the giant African snail, Achatina fulica Férussac, has been studied. 2. Achacin kills both gram-positive and gram-negative bacteria, but only in their growing states. 3. Achacin does not have any bacteriolytic activity. 4. The strain which has no cell wall is a little more sensitive than the native strain and the cell membrane-damaged strain. 5. Achacin was observed on the cytoplasmic membrane and on the cell wall of treated Escherichia coli by immunoelectron microscopy. 6. Achacin attacks the cytoplasmic membrane of the cell.

Cecropia immunoresponsive factor, an insect immunoresponsive factor with DNA-binding properties similar to nuclear-factor kappa B

The immune genes in Hyalophora cecropia contain an upstream sequence that is homologous to the binding site of the mammalian nuclear-factor kappa B (NF-kappa B). These genes are strongly induced by bacteria, lipopolysaccharides and 4 beta-phorbol 12-myristate 13-acetate. Induction of the immune genes involves the activation of a DNA-binding protein complex that we have named Cecropia immunoresponsive factor (CIF). CIF specifically recognizes the kappa B-like DNA sequences in the promoter regions of the Cecropia immune genes. The DNA binding activity of CIF correlates well with the transcriptional induction of the immune genes. Competition assays show that CIF has a DNA binding specificity similar to mammalian NF-kappa B. The two factors also share other characteristics, including the pattern of induction and the migration on the native gel.

Shortened cecropin A-melittin hybrids. Significant size reduction retains potent antibiotic activity

We have earlier reported two 26-residue antibacterial peptides made up from different segments of cecropin A (CA) and melittin (M). We now report a substantial reduction in size at the C-terminal section of the highly active hybrid CA(1-8)M(1-18), leading to a series of 20-, 18- and 15-residue analogs with antibiotic properties similar to the larger molecule. In particular, the 15-residue hybrids CA(1-7)M(2-9), CA(1-7)M(4-11) and CA(1-7)M(5-12) are the shortest cecropin-based peptide antibiotics described so far, with antibacterial activity and spectra similar or better than cecropin A and a 60% reduction in size. Their reduced size and highly alpha-helical structure require an alternative mechanism for their interaction with bacterial membranes.

Action spectrum of antiviral factor from chicken sera

Rous sarcoma virus infections of regressor line chickens stimulate the transient production of antiviral factors in the serum. Earlier the present authors reported that a viral neutralization factor (VNF) inactivated Rous sarcoma virus during a 3-h incubation. The VNF is likely to have a broad antiviral and antimicrobial spectrum because it is active against several unrelated pathogenic poultry viruses. The present study measured the activity of VNF against Newcastle disease virus, infectious bursal disease virus, and infectious bronchitis virus. The VNF is active in immunologically incompetent systems and must be preincubated with the virus in order to inhibit it. Based upon the current experiments, it is proposed that VNF is not an immunomodulator but directly inactivates the virus. The VNF agent appears to be one of a newly identified class of nonspecific antiviral agents produced in vivo in chickens in response to a viral infection.

Biologically active and amidated cecropin produced in a baculovirus expression system from a fusion construct containing the antibody-binding part of protein A

A synthetic antibody-binding part derived from protein A from Staphylococcus aureus was used as a fusion partner in a eukaryotic expression system employing Autographa californica nuclear polyhedrosis as a vector. This, in conjunction with an efficient signal sequence, facilitated the purification of the antibacterial peptide cecropin A from the medium of Spodoptera frugiperda cells infected with a recombinant virus. In order to increase further the concentrations of fusion protein, Trichoplusia ni larvae were used as host. Cecropin A could be obtained after cleavage of the fusion protein with CNBr. Biological activity as well as the correct structure including the C-terminal amide group was shown using electrophoresis with detection of antibacterial proteins and mass spectroscopy.

Attacin, an antibacterial protein from Hyalophora cecropia, inhibits synthesis of outer membrane proteins in Escherichia coli by interfering with omp gene transcription

Attacins are antibacterial proteins synthesized by pupae of the giant silk moth, Hyalophora cecropia, in response to a bacterial infection. In this report we show that the previously described, attacin-induced alteration in the structure and the permeability of the outer membrane of Escherichia coli is associated with a specific inhibition of the synthesis of several outer membrane proteins, including OmpC, OmpF, OmpA, and LamB. The inhibition is expressed as a reduction in the steady-state mRNA levels and is at least in part the results of a block in transcription of the corresponding genes. Transcription directed by the promoter of ompR, the positive regulator of ompC and ompF expression in response to environmental conditions, is also affected by attacin. The effects on mutant strains show that the primary activity of attacin is not mediated by the ompR-envZ regulatory system. Instead our data suggest the existence in E. coli of a previously unknown system for the transcriptional regulation of a large set of outer membrane proteins previously not known to be coordinately regulated. We propose that the activity of attacin is directed towards this system.

Expression of post-translational processing of preprocecropin A using a baculovirus vector

A cDNA fragment encoding preprocecropin A was inserted into the baculovirus Autographa californica nuclear polyhedrosis virus downstream of the polyhedrin promoter. The gene was expressed in recombinant-infected last instar larvae of Trichoplusia ni and in diapausing pupae of Hyalophora cecropia. The identity of the recombinant product was established by electrophoresis with detection of antibacterial activity and mass spectrometry. The prepropeptide had been correctly processed including removal of signal peptide and pro-part. Biologically active and amidated cecropin A was exported to the hemolymph. The yield of recombinant protein in H. cecropia reached a level of 600 micrograms/ml hemolymph and about 70% of the material was amidated.

A structural correlation between lentivirus transmembrane proteins and natural cytolytic peptides

Although oncoviruses and lentiviruses replicate by similar mechanisms, they differ fundamentally in the usual fate of the infected host cell during productive natural infections. Oncoviruses typically establish persistent nonlytic infections in natural host cells, while lentivirus infections characteristically result in a variety of cytopathic effects ultimately leading to death of the target cell. Described here is a unique structural motif consisting of a strongly amphipathic and arginine-rich helical peptide segment in the carboxyl end of lentivirus TM proteins that is structurally similar to the family of cytolytic peptides produced as defensive agents by certain insects and amphibians. Also demonstrated is the lytic nature of synthetic peptides constructed from the transmembrane (TM) protein of human and simian immunodeficiency viruses (HIV and SIV). Thus, it appears that the cytopathic properties of lentiviruses may be in part attributed to the presence of lytic peptides within the TM protein, designated lentivirus lytic peptide (LLP) and that variations in this segment could account for some of the differences observed in the cytopathicity among variants of a particular lentivirus.

A technique for detecting antifungal activity of proteins separated by polyacrylamide gel electrophoresis

A technique was developed for the detection of antifungal activity of proteins after discontinuous polyacrylamide gel electrophoresis under native conditions. The antifungal activity is detected as growth inhibition zones in a homogeneous fungal lawn, grown in an agar layer spread on top of the polyacrylamide gel. The position of proteins with antifungal activity can be determined on a diffusion blot prepared from the same gel. The technique is illustrated for three antifungal plant proteins, i.e. alpha-purothionin, Urtica dioica agglutinin, and tobacco chitinase.

Structure and expression of the attacin genes in Hyalophora cecropia

To study the regulation of the immune genes in insects, we have cloned and sequenced the attacin gene locus of the giant silk moth Hyalophora cecropia. The locus contains one acidic and one basic attacin gene as well as two pseudogenes, which are remnants of basic attacin genes. A small insertion element was found within the locus. The two functional attacin genes are transcribed in opposite directions and have two introns inserted at homologous positions. A common sequence, GGGGATTCCT, is found at nucleotide position -48 in the acidic gene and at nucleotide position -58 in the basic gene. Interestingly, this decanucleotide is similar to the consensus of the NF-k B-binding site. Expression studies revealed that both attacins are strongly induced by phorbol 12-myristate 13-acetate, lipopolysaccharide and bacteria. However, only the acidic attacin gene showed a clear response to injury.

Mosquito host influences on development of filariae

A brief review is presented of the literature relating to factors which limit the capacity of filariae to develop in mosquitoes, with particular emphasis on immune mechanisms. Most insects respond to bacterial infection by the production of potent antibacterial proteins, but little is known of this aspect of the immune response in mosquitoes or of the possible influence of immune proteins on the fate of filarial infections in mosquitoes. A summary account is given of recent experiments with the mosquito Aedes aegypti which involve passive transfer of immune haemolymph together with its in vitro assay and SDS-PAGE examination for induced proteins. These experiments demonstrate the production, in response to inoculation with Brugia pahangi, Escherichia coli, and various components of microbial cell walls, of haemolymph factors which are protective against filarial infection. It remains to be seen whether mosquitoes can produce a specific protective response to infection with eukaryotic organisms such as filaria that is distinctive from that mobilized against bacteria.

Analysis of a gene cluster for sarcotoxin II, a group of antibacterial proteins of Sarcophaga peregrina

Sarcotoxin II is a group of antibacterial proteins of Sarcophaga peregrina (flesh fly) with related primary structures. We have cloned three genes in this family. These genes formed a tandem array with about 2-kb intervals, and one of them was present in the opposite strand. The putative amino acid sequences of the proteins encoded by these genes were very similar except for a deletion in one of them. All of the genes were found to be activated transiently in the same way when the larval body wall was injured, suggesting that the encoded proteins are acute-phase-responsive proteins for protecting the insect from bacterial infection.

Production of recombinant sarcotoxin IA in Bombyx mori cells

A cDNA for sarcotoxin IA, an antibacterial protein of Sarcophaga peregrina (fleshfly), was inserted into a silkworm baculovirus vector and expressed in Bm-N cells, a line of Bombyx mori cells. When a cysteine proteinase inhibitor, p-chloromercuribenzenesulphonic acid, was present in the culture medium, a significant amount of recombinant sarcotoxin IA accumulated, but without this reagent the product seemed to be degraded in this system. The C-terminus of the recombinant sarcotoxin IA seemed to be glycine, not amidated arginine as found in authentic sarcotoxin IA. Probably, Bm-N cells lack the C-terminal alpha-amidation enzyme.

Analysis of a gene cluster for sarcotoxin II, a group of antibacterial proteins of Sarcophaga peregrina

Sarcotoxin II is a group of antibacterial proteins of Sarcophaga peregrina (flesh fly) with related primary structures. We have cloned three genes in this family. These genes formed a tandem array with about 2-kb intervals, and one of them was present in the opposite strand. The putative amino acid sequences of the proteins encoded by these genes were very similar except for a deletion in one of them. All of the genes were found to be activated transiently in the same way when the larval body wall was injured, suggesting that the encoded proteins are acute-phase-responsive proteins for protecting the insect from bacterial infection.

Antibacterial activity in the hemolymph of myriapods (Arthropoda)

The hemolymphs of two diplopod (Chicobolus sp. and Rhapidostreptus virgator) and two chilopod species (Lithobius forficatus and Scolopendra cingulata) were tested for the presence of antibacterial substances using Petri dish tests. The native hemolymph of all species had substances acting on living Micrococcus luteus, whereas only Rhapidostreptus, Scolopendra, and Lithobius were effective against lyophilized Micrococcus. The antibacterial activity against living Micrococcus increased after inoculation with bacteria (Enterobacter cloacae beta-12) in Chicobolus and Rhapidostreptus and also against lyophilized Micrococcus in the latter. Thus, these effects appear to be inducible. None of the myriapods tested had any bacteriostatic effect on Escherichia coli D-31 whereas the growth of gram-negative E. cloacae was inhibited. The antibacterial substances in the diplopod species were unstable when heated but were resistant to freezing. At least two antibacterial substances (a lysozyme-like one and another substance) are considered to occur in Myriapoda.

All-D amino acid-containing channel-forming antibiotic peptides

The D enantiomers of three naturally occurring antibiotics--cecropin A, magainin 2 amide, and melittin--were synthesized. In addition, the D enantiomers of two synthetic chimeric cecropin-melittin hybrid peptides were prepared. Each D isomer was shown by circular dichroism to be a mirror image of the corresponding L isomer in several solvent mixtures. In 20% hexafluoro-2-propanol the peptides contained 43-75% alpha-helix. The all-D peptides were resistant to enzymatic degradation. The peptides produced single-channel conductances in planar lipid bilayers, and the D and L enantiomers caused equivalent amounts of electrical conductivity. All of the peptides were potent antibacterial agents against representative Gram-negative and Gram-positive species. The D and L enantiomers of each peptide pair were equally active, within experimental error. Sheep erythrocytes were lysed by both D- and L-melittin but not by either isomer of cecropin A, magainin 2 amide, or the hybrids cecropin A-(1-13)-melittin-(1-13)-NH2 or cecropin A-(1-8)-melittin-(1-18)-NH2. The infectivity of the bloodstream form of the malaria parasite Plasmodium falciparum was also inhibited by the D and L hybrids. It is suggested that the mode of action of these peptides on the membranes of bacteria, erythrocytes, plasmodia, and artificial lipid bilayers may be similar and involves the formation of ion-channel pores spanning the membranes, but without specific interaction with chiral receptors or enzymes.

Hemolysins: pore-forming proteins in invertebrates

Invertebrates possess lytic molecules which lyse vertebrate erythrocytes. In all the species studied so far, hemolytic activity depends on proteins which possess a wide range of reactivity. It is generally calcium-dependent and heat-labile, although calcium-independent and heat-stable hemolysins have also been detected. The molecules interact with sugars or lipids which could represent the membrane receptors by which circular lesions on target membranes are produced. On the basis of some analogies with vertebrate lytic molecules it is conceivable that the hemolysins evolved from a common ancestral gene which also led to vertebrate pore-forming proteins.