Cell-free immunity in Cecropia. A model system for antibacterial proteins

Amphipathic Helices from Aromatic Amino Acid Oligomers

Synthetic helical foldamers are of significant interest for mimicking the conformations of naturally occurring molecules while at the same time introducing new structures and properties. In particular, oligoamides of aromatic amino acids are attractive targets, as their folding is highly predictable and stable. Here the design and synthesis of new amphipathic helical oligoamides based on quinoline-derived amino acids having either hydrophobic or cationic side chains are described. Their structures were characterized in the solid state by single-crystal X-ray diffraction and in solution by NMR. Results of these studies suggest that an oligomer as short as a pentamer folds into a stable helical conformation in protic solvents, including MeOH and H(2)O. The introduction of polar proteinogenic side chains to these foldamers, as described here for the first time, promises to provide possibilities for the biological applications of these molecules. In particular, amphipathic helices are versatile targets to explore due to their importance in a variety of biological processes, and the unique structure and properties of the quinoline-derived oligoamides may allow new structure-activity relationships to be developed.

Interactions between the plasma membrane and the antimicrobial peptide HP (2-20) and its analogues derived from Helicobacter pylori

HP (2-20), a 19-residue peptide derived from the N-terminus of Helicobacter pylori ribosomal protein L1, has antimicrobial activity but is not cytotoxic to human erythrocytes. We synthesized several peptide analogues to investigate the effects of substitutions on structure and antimicrobial activity. Replacement of Gln16 and Asp18 with tryptophan [anal-3 (analogue-3)] caused a dramatic increase in lytic activities against bacteria and fungi. By contrast, a decrease in amphiphilicity caused by replacement of Phe5 or Leu11 with serine was accompanied by a reduction in antimicrobial activity. Analysis of the tertiary structures of the peptides in SDS micelles by NMR spectroscopy revealed that they have a well-defined a-helical structure. Among the analogues, anal-3 has the longest a-helix, from Val4 to Trp18. The enhanced hydrophobicity and increased a-helicity results in enhanced antimicrobial activity in anal-3 without an increase in haemolytic activity. Fluorescence experiments proved that the bacterial-cell selectivity of the anal-3 peptide is due to its high binding affinity for negatively charged phospholipids in bacterial cells. Results showing the effect of spin-labels on the NMR spectra indicated that the side chains in the hydrophobic phase of the amphiphilic a-helix are buried on the surface of the micelle and the tryptophan indole ring is anchored in the membrane surface. Because anal-3 shows high selectivity towards bacterial and fungal cells, it may provide an avenue for the development of new antibiotics.

Innate immunity in human bone

Bone has exceptional regenerative properties. Oral bone appears to be particularly resistant to infection despite exposure to oral flora, even in circumstances such as oral surgery where the thin mucosal layer covering the bone is disrupted. The goal of this study was to determine whether the innate immune system of antimicrobial peptides exists inside bone. Biopsies of non-infected and chronically infected mandibular bone were harvested from patients during maxillofacial surgical procedures. Bone biopsies from the iliac crest and fibula served as controls. Immunohistochemical staining was performed, directed against the human beta-defensin antimicrobial peptides (hBD) -1, -2 and -3. In addition, cultures of osteoblast-like cells were examined for the presence of each of the three beta-defensins and their mRNA transcripts. All three human beta-defensins were detected within the mineralized bone matrix of chronically infected mandibular bone in the vicinity of the endosteum and osteocytes. hBD-1, -2 and -3 were also found in the cytoplasm of osteocytes. Expression of all three beta-defensins was detected in each of the non-infected bone types including the controls, however, to a lesser degree than that found in the chronically infected mandibular bone. This may reflect upregulation of antimicrobial peptide expression in the presence of chronic infection. Cultures of non-infected osteoblast-like cells were found to express mRNA for each of hBD-1, -2 and -3. Immunohistochemical staining of the cultures was positive for hBD-1 and -2, but not for hBD-3. We provide the first evidence of a previously unrecognized innate immunological function of bone through the demonstration of the presence of the human beta-defensins hBD-1, -2 and -3 in bone.

Effects of cecropin B transgene expression on Mannheimia haemolytica serotype 1 colonization of the nasal mucosa of calves

OBJECTIVE

To express a cecropin B transgene on bovine nasal mucosa and determine the effect on Mannheimia haemolytica serotype 1 (S1) colonization.

ANIMALS

27 crossbred beef calves.

PROCEDURE

The antibacterial efficacy of cecropin B against M. haemolytica S1 was first determined by measuring its minimum inhibitory concentration (MIC). The peptide was also diluted in pooled bovine nasal secretions, and its antibacterial activity was evaluated. The nasal passages of 16 calves were aerosolized with 25, 50, or 100 microg of plasmid DNA/nostril, whereas 11 control calves were aerosolized with only the transfection reagent. In 2 of the experiments, 12 treated and 8 control calves were exposed intranasally with an aerosol of M. haemolytica S1. Nasal swab specimens and secretions were collected and analyzed by use of polymerase chain reaction (PCR), real-time PCR, real-time reverse-transcriptase PCR, ELISA, and bacterial culture.

RESULTS

In vitro, cecropin B inhibited M. haemolytica S1 at an MIC of 2 microg/mL and its antibacterial activity was not affected by proteolytic activity in nasal secretions. Cecropin B transgene expression was detected in calves transfected with 50 or 100 microg of DNA/nostril. Antibacterial activity against M. haemolytica S1 was observed in all calves transfected with 100 microg of DNA/nostril but in only 2 of the 4 calves transfected with 50 microg of DNA/nostril.

CONCLUSIONS AND CLINICAL RELEVANCE

In vitro, cecropin B has an effective antibacterial activity against M. haemolytica S1 and can prevent colonization of the nasal mucosa after transfection of a vector expressing cecropin B in vivo.

Cecropin P1 and novel nematode cecropins: a bacteria-inducible antimicrobial peptide family in the nematode Ascaris suum

Cecropin P1 was first identified as a mammalian antimicrobial peptide isolated from the pig intestine. Much research aimed at characterizing this peptide has been reported. Recently, the workers who discovered the peptide corrected their original conclusion, and confirmed that this peptide originates in fact from the pig intestinal parasitic nematode, Ascaris suum. In the present study, we carried out a semi-exhaustive search for bacteria-inducible transcripts in A. suum by the cDNA subtraction method. The transcripts encoding cecropin P1 and novel Ascaris cecropins, designated cecropins P2, P3 and P4, were found to be positively induced factors. Chemically synthesized Ascaris cecropins were bactericidal against a wide range of microbes, i.e. Gram-positive (Staphylococcus aureus, Bacillus subtilis and Micrococcus luteus) and Gram-negative (Pseudomonas aeruginosa, Salmonella typhimurium, Serratia marcescens and Esherichia coli) bacteria, and were weakly but detectably active against yeasts (Saccharomyces cerevisiae and Candida albicans). Cecropin P1-like sequences were also detected at least in two other species (Ascaris lumbricoides and Toxocara canis) of the Ascarididae. All Ascaris cecropin precursors contain an acidic pro-region connected by a tetra-basic cleavage site at the C-terminus. Such an acidic pro-region is also reported to be present in the tunicate cecropin-type antimicrobial peptide styelin. On the basis of the evolutionary position of nematodes and tunicates, the ancestral cecropin may have contained the acidic pro-region at the C-terminus.

Effects of N- and C-terminal truncation of HP (2-20) from Helicobacter pylori ribosomal protein L1 (RPL1) on its anti-microbial activity

HP (2-20) [derived from the N-terminal region of Helicobacter pylori Ribosomal Protein L1 (RPL1)], a 19-mer peptide, possesses broad-spectrum anti-microbial activity. As the N- (residues 2-3) and C-terminal (residues 14-20) residues can be deleted without affecting antimicrobial activity, we have now determined the minimum chain length necessary for the retention of antimicrobial activity, and its mode of action. The N- (residues 2-3) and C-terminal (residues 17-20) truncated fragments [HP (4-16)] induce increased antibiotic activity against several bacterial strains without hemolysis. Flow cytometric analysis, scanning electron microscopy and fluorescence confocal microscopy revealed that HP (4-16) acted rapidly on the plasma membranes of the fungal cells in a salt- and energy-independent manner.

Antibiotic activity and synergistic effect of antimicrobial peptide against pathogens from a patient with gallstones

HP (2-20) is a peptide derived from the N-terminus of Helicobacter pylori ribosomal protein L1 that has been shown to have antimicrobial activity against various species of bacteria. When we tested the effects of HP (2-20), we found that this peptide displayed strong activity against pathogens from a patient with gallstones, but it did not have hemolytic activity against human erythrocytes. We also found that HP (2-20) had potent activity against cefazolin sodium-resistant bacterial cell lines, and that HP (2-20) and cefazolin sodium had synergistic effects against cell lines resistant to the latter. To investigate the mechanism of action of HP (2-20), we performed fluorescence activated flow cytometry using pathogens from the patient with gallstones. As determined by propidium iodide (PI) staining, pathogenic bacteria treated with HP (2-20) showed higher fluorescence intensity than untreated cells, similar to melittin-treated cells, and that HP (2-20) acted in an energy- and salt-dependent manner. Scanning electron microscopy showed that HP (2-20) caused significant morphological alterations in the cell surface of pathogens from the patient with gallstones. By determining their 16S rDNA sequences, we found that both the pathogens from the patient with gallstones and the cefazolin sodium-resistant cell lines showed 100% homology with sequences from Pseudomonas aeruginosa. Taken together, these results suggest that HP (2-20) has antibiotic activity and that it may be used as a lead drug for the treatment of acquired pathogens from patients with gallstones and antibiotic-resistant cell lines.

Host protection against deliberate bacterial contamination of an extracellular matrix bioscaffold versus Dacron mesh in a dog model of orthopedic soft tissue repair

The resistance of two biomaterials, one synthetic and one biologic in origin, to deliberate bacterial infection was compared in a dog model of orthopedic soft tissue reconstruction. Twenty-four adult female dogs were randomly divided into two equal groups and a 2.0-cm-round full-thickness defect was created on the lateral surface of the stifle joint, leaving only the synovium and skin intact. The defect was surgically repaired with either Dacron trade mark mesh or a porcine derived extracellular matrix (ECM) scaffold material. The repair site was inoculated with 1 x 10(8) Staphylococcus aureus at the time of surgery and the dogs were survived for 28 days. Results showed a chronic pyogranulomatous inflammatory response at the Dacron trade mark implant sites versus a constructive tissue-remodeling response without residual inflammation at the ECM implant site. Three dogs in the group receiving the Dacron trade mark mesh were treated with Keflex trade mark (500 mg bid x 7 days) for signs of septicemia. A quantitative bacterial count of the implant sites at the time of sacrifice showed 6.52 x 10(5) +/- 1.2 x 10(6) and 6.5 x 10(2) +/- 1.8 x 10(3) bacteria per gram of tissue for the Dacron trade mark and ECM scaffold sites, respectively (P <.03). The ECM implant material was more resistant than the synthetic implant material to persistent infection following deliberate bacterial contamination and the ECM scaffold supported constructive tissue remodeling.

An entomopathogenic bacterium, Xenorhabdus nematophila, inhibits the expression of an antibacterial peptide, cecropin, of the beet armyworm, Spodoptera exigua

An entomopathogenic bacterium, Xenorhabdus nematophila, is known to depress hemocyte nodule formation of target insects by inhibiting eicosanoid biosynthesis. This study analyzed the inhibitory effect of X. nematophila on the humoral immunity of the target insects and tested its association with the host eicosanoid pathway. Plasma collected from the fifth instar larvae of Spodoptera exigua, when they were injected with X. nematophila, did not show antibacterial activity against Escherichia coli by a growth inhibition zone assay. In comparison, heat-killed X. nematophila induced significant antibacterial activity in the plasma. The antibacterial humoral activity was further demonstrated by examining a specific potent antibacterial peptide, cecropin. Two cecropin genes ('A' and 'B') were partially cloned from the fifth instar larvae of S. exigua by conserved degenerate primers using nested reverse transcriptase-polymerase chain reaction (RT-PCR). They showed high homologies with known cecropins from other lepidopteran species. Northern analysis using the cecropin probe showed that the injection of the heat-killed X. nematophila induced significant expression of a cecropin mRNA transcript (approximately 1.1 kb), but the larvae injected with the live bacteria did not show the corresponding transcript. Injection of arachidonic acid did not rescue the inhibition of X. nematophila based on either antibacterial activity or cecropin gene expression. The addition of dexamethasone, a specific phospholipase A2 inhibitor, did not inhibit antibacterial activity or cecropin gene expression when the larvae were injected with heat-killed X. nematophila. These results suggest that X. nematophila inhibits the antibacterial humoral immune reaction as well as the cellular immune reaction in S. exigua and that the inhibition of X. nematophila on the expression of the antibacterial peptide is not associated with inhibition of the eicosanoid pathway.

Lysozyme of the beet armyworm, Spodoptera exigua: activity induction and cDNA structure

Lysozyme of the beet armyworm, Spodoptera exigua, was characterized in its up-regulation pattern, and its cDNA was cloned by RT-PCR using degenerate primers designed from some conserved amino acid regions shared with related lepidopteran species. Lysozyme activity of the non-immunized S. exigua had developmental variation, with the highest level in the fifth instar larvae. The basal level of the lysozyme activity was significantly enhanced by the injection of laminarin or lipopolysaccharide (LPS). Among different LPSs tested, the extract from an entomopathogenic bacterium, Xenorhabdus nematophilus, proved to be the most potent. Fat body was the major tissue to express the lysozyme in S. exigua. Even though there was a significantly elevated level of lysozyme in the hemolymph at 12 h after laminarin injection, the transcript ( approximately 1.1 kbp) was found in the fat body as early as 6 h after injection. The cDNA of the lysozyme was cloned as 602 bp with a deduced 141-amino-acid residue open reading frame containing two introns. Except for a signal peptide with 20 amino acid residues, the estimated molecular weight and isoelectric point of the lysozyme was 14313.83 Da and 8.59, respectively. Only a single copy gene of the lysozyme was found in S. exigua genome from Southern analysis. The amino acid sequence of S. exigua lysozyme showed higher similarity (88.7%) with noctuid species compared to other lepidopteran species.

The ceratotoxin gene family in the medfly Ceratitis capitata and the Natal fruit fly Ceratitis rosa (Diptera: Tephritidae)

Ceratotoxins (Ctxs) are a family of antibacterial sex-specific peptides expressed in the female reproductive accessory glands of the Mediterranean fruit fly Ceratitis capitata. As a first step in the study of molecular evolution of Ctx genes in Ceratitis, partial genomic sequences encoding four distinct Ctx precursors have been determined. In addition, anti-Escherichia coli activity very similar to that of the accessory gland secretion from C. capitata was found in the accessory gland secretion from Ceratitis (Pterandrus) rosa. SDS-PAGE analysis of the female reproductive accessory glands from C. rosa showed a band with a molecular mass (3 kDa) compatible with that of Ctx peptides, also slightly reacting with an anti-Ctx serum. Four nucleotide sequences encoding Ctx-like precursors in C. rosa were determined. Sequence and phylogenetic analyses show that Ctxs from C. rosa fall into different groups as C. capitata Ctxs. Our results suggest that the evolution of the ceratotoxin gene family might be viewed as a combination of duplication events that occurred prior to and following the split between C. capitata and C. rosa. Genomic hybridization demonstrated the presence of multiple Ctx-like sequences in C. rosa, but low-stringency Southern blot analyses failed to recover members of this gene family in other tephritid flies.

Protein purification, cDNA cloning and gene expression of attacin, an antibacterial protein, from eri-silkworm, Samia cynthia ricini

Attacin was isolated from immunized larval hemolymph of the wild silkmoth, Samia cynthia ricini. The antibacterial effect of the attacin was limited to some species of Gram-negative bacteria. Two cDNA clones encoding attacin A and B, respectively, were isolated by screening the cDNA library from immunized fat body. The two cDNAs encoded the same length of precursor protein with 233 amino acid residues. The 46-residue prepropeptides of the two attacins were identical to each other, but 4 out of 187 residues of the mature proteins were different in each other. The two attacins show 98% identity at the amino acid level, while 92% identity at the nucleotide level. Both of the mature proteins were highly homologous to cecropia basic attacin with identity of 96%. The attacin transcripts were detected at significant level in fat body, hemocytes and Malpighian tube after injection with peptidoglycan, but not in the midgut and the silkgland. The induction of attacin gene expression was elicited most effectively by peptidoglycan and UV-killed bacteria in the fat body.

Design of novel analogue peptides with potent antibiotic activity based on the antimicrobial peptide, HP (2-20), derived from N-terminus of Helicobacter pylori ribosomal protein L1

HP (2-20) (AKKVFKRLEKLFSKIQNDK) is the antimicrobial sequence derived from the N-terminus of Helicobacter pylori ribosomal protein L1 (RPL1). In order to develop novel antibiotic peptides useful as therapeutic agents, potent antibiotic activities against bacteria, fungi and cancer cells without a cytotoxic effect are essential. To this end, several analogues with amino acid substitutions were designed to increase or decrease only the net hydrophobicity. In particular, the substitution of Trp for the hydrophobic amino acids, Gln and Asp at positions 17 and 19 of HP (2-20) (Anal 3), caused a dramatic increase in antibiotic activity without a hemolytic effect. In contrast, the decrease of hydrophobicity brought about by substituting Ser for Leu and Phe at positions 12 and 19 of HP (2-20), respectively (Anal 4, Anal 5), did not have a significant effect on the antibiotic activity. The antibiotic effects of these synthetic peptides were further investigated by treating prepared protoplasts of Candida albicans and conducting an artificial liposomal vesicle (PC/PS; 3:1, w/w) disrupting activity test. The results demonstrated that the Anal 3 prevented the regeneration of fungal cell walls and induced an enhanced release of fluorescent dye (carboxyfluorescein) trapped in the artificial membrane vesicles to a greater degree than HP (2-20). The potassium-release test conducted on C. albicans indicated that Anal 3 induced greater amounts of potassium ion to be released than the parent peptide, HP (2-20) did. These results indicated that the hydrophobic region of peptides is prerequisite for its effective antibiotic activity and may facilitate easy penetration of the lipid bilayers of the cell membrane.

Antifungal mechanism of SMAP-29 (1-18) isolated from sheep myeloid mRNA against Trichosporon beigelii

The antifungal activity and mechanism of SMAP-29 (1-18) (SMAP-29), a cathelicidin-derived antimicrobial peptide deduced from N-terminal sequence of sheep myeloid mRNA, were investigated. SMAP-29 displayed a strong antifungal activity against various fungi. To understand the antifungal mechanism(s) of SMAP-29, we examined the interaction of SMAP-29 with the pathogenic fungus Trichosporon beigelii. Confocal microscopy showed that SMAP-29 was localized in the plasma membrane. The antifungal effects of SMAP-29 were further confirmed by using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a plasma membrane probe. Flow cytometric analysis revealed that SMAP-29 acted in an energy-dependent manner. This interaction is also dependent on the ionic environment. Furthermore, SMAP-29 caused significant morphological changes when testing the membrane disrupting activity using liposomes (phosphatidylcholine/cholesterol; 10:1, w/w), as shown by scanning electron microscopy. The results suggest that SMAP-29 may exert its antifungal activity by disrupting the structure of cell membranes, via direct interaction with the lipid bilayers and irregularly disrupted fungal membranes in an energy- and salt-dependent manner.

Design of novel peptide analogs with potent fungicidal activity, based on PMAP-23 antimicrobial peptide isolated from porcine myeloid

PMAP-23 is a 23-mer peptide derived from porcine myeloid. To develop novel antifungal peptides useful as therapeutic drugs, it would require a strong fungicidal activity against pathogenic fungal cells. To this goal, several analogs, with amino acid substitutions, were designed to increase the net hydrophobicity by Trp (W)-substitution at positions 10, 13, or 14 at the hydrophilic face of PMAP-23 without changing the hydrophobic helical face. The Trp (W)-substitution (P6) showed an enhanced fungicidal and antitumor activities, with the fungicidal activity inhibited by salts and the respiratory inhibitor, NaN(3). The results suggested that the increase of hydrophobicity of the peptides correlated with fungicidal activity. The fungicidal effects of analog peptides were further investigated using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a membrane probe. In Candida albicans, the analog peptide (P6) exerted its fungicidal effect on the blastoconidia in 20% fetal bovine serum by disrupting the mycelial forms. Furthermore, P6 caused significant morphological changes, and these facts suggested that the fungicidal function of the novel analog peptide (P6) was by damaging the fungal cell membranes. Thus, this peptide may provide a useful template for designing novel antifungal peptides useful for the treatment of infectious diseases.

Antifungal mechanism of an antimicrobial peptide, HP (2--20), derived from N-terminus of Helicobacter pylori ribosomal protein L1 against Candida albicans

The antifungal activity and mechanism of HP (2-20), a peptide derived from the N-terminus sequence of Helicobacter pylori Ribosomal Protein L1 were investigated. HP (2--20) displayed a strong antifungal activity against various fungi, and the antifungal activity was inhibited by Ca(2+) and Mg(2+) ions. In order to investigate the antifungal mechanism(s) of HP (2-20), fluorescence activated flow cytometry was performed. As determined by propidium iodide staining, Candida albicans treated with HP (2-20) showed a higher fluorescence intensity than untreated cells and was similar to melittin-treated cells. The effect on fungal cell membranes was examined by investigating the change in membrane dynamics of C. albicans using 1,6-diphenyl-1,3,5-hexatriene as a membrane probe and by testing the membrane disrupting activity using liposome (PC/PS; 3:1, w/w) and by treating protoplasts of C. albicans with the peptide. The action of peptide against fungal cell membrane was further examined by the potassium-release test, and HP (2-20) was able to increase the amount of K(+) released from the cells. The result suggests that HP (2-20) may exert its antifungal activity by disrupting the structure of cell membrane via pore formation or directly interacts with the lipid bilayers in a salt-dependent manner.

Cathelicidins: microbicidal activity, mechanisms of action, and roles in innate immunity

Antimicrobial peptides are important host-defense molecules of innate immunity. Cathelicidins are a diverse family of potent, rapidly acting and broadly effective antimicrobial peptides, which are produced by a variety of cells. This review examines the classification, antimicrobial spectrum, mechanism of action, and regulation of cathelicidins.

Antimicrobial activity associated with extracellular matrices

Materials derived from extracellular matrices (ECMs) are being evaluated as scaffolds for surgical reconstruction of damaged or missing tissues. It is important to understand the susceptibility of these biological materials to bacterial infections. ECMs derived from porcine small intestinal submucosa (SIS) and urinary bladder submucosa (UBS) were found to possess antimicrobial activity. ECM extracts, obtained by digesting these acellular matrices in acetic acid, demonstrated antibacterial activity against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Antimicrobial activity was determined using a minimal inhibitory concentration assay. Bacteriostatic activity was detected at protein concentrations of ECM extracts equivalent to 0.77-1.60 mg/mL. ECM extracts were found to inhibit bacterial growth for up to at least 13 h. The resulting extracts consisted of water-soluble peptides and proteins with molecular weights ranging from <4 to >100 kDa and lower molecular weight compounds, as determined by size exclusion liquid chromatography.

A helix-loop-helix peptide at the upper lip of the active site cleft of lysozyme confers potent antimicrobial activity with membrane permeabilization action

Recently, we have found that partially unfolded lysozyme exerts broad spectrum antimicrobial action in vitro against Gram-negative and Gram-positive bacteria independent of its catalytic activity. In parallel, an internal peptide (residues 98-112) of hen egg white lysozyme, obtained after digestion with clostripain, possessed broad spectrum antimicrobial action in vitro. This internal peptide is part of a helix-loop-helix domain (87-114 sequence of hen lysozyme) located at the upper lip of the active site cleft of lysozyme. The helix-loop-helix (HLH) structures are known motifs commonly found in membrane-active and DNA-binding proteins. To evaluate the contribution of the HLH peptide to the antimicrobial properties of lysozyme, the HLH sequence and its secondary structure derivatives of chicken and human lysozyme were synthesized and tested for antimicrobial activity against several bacterial strains. We found that the full HLH peptide of both chicken and human lysozymes was potently microbicidal against both Gram-positive and Gram-negative bacteria and the fungus Candida albicans. The N-terminal helix of HLH was specifically bactericidal to Gram-positive bacteria, whereas the C-terminal helix was bactericidal to all tested strains. Outer and inner membrane permeabilization studies, as well as measurements of transmembrane electrochemical potentials, provided evidence that HLH peptide and its C-terminal helix domain kill Gram-negative bacteria by crossing the outer membrane via self-promoted uptake and causing damage to the inner membrane through channel formation. The results are discussed in terms of proposed mechanisms for the catalytically independent antimicrobial activity of lysozyme that offer a new strategy for the design of potential antimicrobial drugs in the treatment of infectious diseases.

Genetic evidence that antibacterial activity of lysozyme is independent of its catalytic function

A catalytically inactive mutant of hen egg white lysozyme was constructed by site-directed mutagenesis to elucidate the role of enzymatic activity on its antimicrobial activity against Gram-positive bacteria. The catalytic residue aspartic acid at position 52 of lysozyme was substituted with serine (D52S-Lz) and the mutant cDNA was inserted into a yeast expression vector, pYES-2. Western blot analysis indicated that the mutation did not affect secretion of the D52S-Lz lysozyme into the medium of the expressing Saccharomyces cerevisiae, INVSC1. In addition, circular dichroism and fluorescence spectral analysis revealed no change in the structure of D52S-Lz compared to that of wild-type (Wt-Lz) lysozyme. The mutation (D52S) abolished the catalytic activity of lysozyme. Antimicrobial tests against Staphylococcus aureus and Bacillus subtilis revealed that the catalytically inactive D52S-Lz was as bactericidal as the Wt-Lz lysozyme. Heat treatment leading to enzyme inactivation had no effect on the bactericidal activity of either wild-type or the mutant D52S-Lz lysozyme. The binding affinity of D52S-Lz to the isolated peptidoglycan of S. aureus was unaffected. Our results provide the first demonstration of direct genetic evidence that the antimicrobial activity of lysozyme is operationally independent of its muramidase activity, and strongly suggest the antimicrobial action of lysozyme is due to structural factors.

Effects of synthetic cecropin analogs on in vitro growth of Acholeplasma laidlawii

Four synthetic peptides (Peptidyl MIMs; Demeter Biotechnologies, Inc.) were evaluated for their in vitro activity against Acholeplasma laidlawii. Fifty percent effective concentration values ranged from 1 to 15 microM. Three of these compounds are more lethal than cecropin B against A. laidlawii.

De novo design, synthesis, and characterization of antimicrobial beta-peptides

beta-Peptides are a class of polyamides that have been demonstrated to adopt a variety of helical conformations. Recently, a series of amphiphilic L(+2) helical beta-peptides were designed, which were intended to mimic the overall physicochemical properties of a class of membrane-active antimicrobial peptides, including magainin and cecropin. Although these peptides showed potent antimicrobial activity, they also showed significant activity against human erythrocytes. Operating under the assumption that their lack of specificity arose from excessive hydrophobicity, two additional beta-peptides H-(beta(3)-HAla-beta(3)-HLys-beta(3)-HVal)(n)-NH(2) (n = 4, 5) were designed and synthesized. Both have high antimicrobial activities, but very low hemolytic potencies. The peptides bind in an L(+2) conformation to phospholipid vesicles, inducing leakage of entrapped small molecules. The peptides have a low affinity for membranes consisting of neutral phosphatidylcholine lipids, but bind avidly to vesicles containing 10 mol % of acidic phosphatidylserine lipids. Differences in vesicle leakage kinetics for the two peptides suggest that chain length could affect their mechanisms of disrupting cell membranes. Thus, insights gained from the study of variants of natural alpha-peptides have provided a useful guide for the design of nonnatural antimicrobial beta-peptides.

Internalization of tenecin 3 by a fungal cellular process is essential for its fungicidal effect on Candida albicans

Tenecin 3 is a glycine-rich, antifungal protein of 78 residues isolated from the insect Tenebrio molitor larva. As an initial step towards understanding the antifungal mechanism of tenecin 3, we examined how this protein interacts with the pathogenic fungus Candida albicans to exert its antifungal action. Tenecin 3 did not induce the release of a fluorescent dye trapped in the artificial membrane vesicles and it did not perturb the membrane potential of C. albicans by the initial interaction. Fluorescence confocal microscopy and flow cytometric analysis revealed that tenecin 3 is rapidly internalized into the cytoplasmic space in energy-dependent and temperature-dependent manners. This internalization is also dependent on the ionic environment and cellular metabolic states. These results suggest that the internalization of tenecin 3 into the cytoplasm of C. albicans is mediated by a fungal cellular process. The internalized tenecin 3 is dispersed in the cytoplasm, and the loss of cell viability occurs after this internalization.

Protein purification, cDNA cloning and gene expression of lysozyme from eri-silkworm, Samia cynthia ricini

Lysozyme was isolated from immunized hemolymph of Samia cynthia ricini larvae by heat treatment, cation exchange and reverse-phase chromatography. A cDNA encoding lysozyme was cloned by screening the cDNA library from immunized fat body using, as a probe, a DNA fragment obtained by PCR-based differential display method. The deduced amino acid sequence showed high homology with other chicken-type lysozymes. The calculated molecular mass of the mature peptide was 13785, which agreed precisely with that obtained by MALDI-TOF mass spectrometry of the isolated protein. The lysozyme transcripts were detected at a significant level in naïve fat body, and the level increased 5-10-fold upon injection of the larvae with UV-killed bacteria or peptidoglycan.

Amphipathic, alpha-helical antimicrobial peptides

Gene-encoded antimicrobial peptides are an important component of host defense in animals ranging from insects to mammals. They do not target specific molecular receptors on the microbial surface, but rather assume amphipathic structures that allow them to interact directly with microbial membranes, which they can rapidly permeabilize. They are thus perceived to be one promising solution to the growing problem of microbial resistance to conventional antibiotics. A particularly abundant and widespread class of antimicrobial peptides are those with amphipathic, alpha-helical domains. Due to their relatively small size and synthetic accessibility, these peptides have been extensively studied and have generated a substantial amount of structure-activity relationship (SAR) data. In this review, alpha-helical antimicrobial peptides are considered from the point of view of six interrelated structural and physicochemical parameters that modulate their activity and specificity: sequence, size, structuring, charge, amphipathicity, and hydrophobicity. It begins by providing an overview of how these vary in peptides from different natural sources. It then analyzes how they relate to the currently accepted model for the mode of action of alpha-helical peptides, and discusses what the numerous SAR studies that have been carried out on these compounds and their analogues can tell us. A comparative analysis of the many alpha-helical, antimicrobial peptide sequences that are now available then provides further information on how these parameters are distributed and interrelated. Finally, the systematic variation of parameters in short model peptides is used to throw light on their role in antimicrobial potency and specificity. The review concludes with some considerations on the potentials and limitations for the development of alpha-helical, antimicrobial peptides as antiinfective agents.

Role of the hinge region and the tryptophan residue in the synthetic antimicrobial peptides, cecropin A(1-8)-magainin 2(1-12) and its analogues, on their antibiotic activities and structures

A 20-residue hybrid peptide CA(1-8)-MA(1-12) (CA-MA), incorporating residues 1-8 of cecropin A (CA) and residues 1-12 of magainin 2 (MA), has potent antimicrobial activity without toxicity against human erythrocytes. To investigate the effects of the Gly-Ile-Gly hinge sequence of CA-MA on the antibacterial and antitumor activities, two analogues in which the Gly-Ile-Gly sequence of CA-MA is either deleted (P1) or substituted with Pro (P2) were synthesized. The role of the tryptophan residue at position 2 of CA-MA on its antibiotic activity was also investigated using two analogues, in which the Trp2 residue of CA-MA is replaced with either Ala (P3) or Leu (P4). The tertiary structures of CA-MA, P2, and P4 in DPC micelles, as determined by NMR spectroscopy, have a short amphiphilic helix in the N-terminus and about three turns of alpha-helix in the C-terminus, with the flexible hinge region between them. The P1 analogue has an alpha-helix from Leu4 to Ala14 without any hinge structure. P1 has significantly decreased lytic activities against bacterial and tumor cells and PC/PS vesicles (3:1, w/w), and reduced pore-forming activity on lipid bilayers, while P2 retained effective lytic activities and pore-forming activity. The N-terminal region of P3 has a flexible structure without any specific secondary structure. The P3 modification caused a drastic decrease in the antibiotic activities, whereas P4, with the hydrophobic Leu side chain at position 2, retained its activities. On the basis of the tertiary structures, antibiotic activities, vesicle-disrupting activities, and pore-forming activities, the structure-function relationships can be summarized as follows. The partial insertion of the Trp2 of CA-MA into the membrane, as well as the electrostatic interactions between the positively charged Lys residues at the N-terminus of the CA-MA and the anionic phospholipid headgroups, leads to the primary binding to the cell membrane. Then, the flexibility or bending potential induced by the Gly-Ile-Gly hinge sequence or the Pro residue in the central part of the peptides may allow the alpha-helix in the C-terminus to span the lipid bilayer. These structural features are crucial for the potent antibiotic activities of CA-MA.

Antibacterial peptides isolated from insects

Insects are amazingly resistant to bacterial infections. To combat pathogens, insects rely on cellular and humoral mechanisms, innate immunity being dominant in the latter category. Upon detection of bacteria, a complex genetic cascade is activated, which ultimately results in the synthesis of a battery of antibacterial peptides and their release into the haemolymph. The peptides are usually basic in character and are composed of 20-40 amino acid residues, although some smaller proteins are also included in the antimicrobial repertoire. While the proline-rich peptides and the glycine-rich peptides are predominantly active against Gram-negative strains, the defensins selectively kill Gram-positive bacteria and the cecropins are active against both types. The insect antibacterial peptides are very potent: their IC50 (50% of the bacterial growth inhibition) hovers in the submicromolar or low micromolar range. The majority of the peptides act through disintegrating the bacterial membrane or interfering with membrane assembly, with the exception of drosocin, apidaecin and pyrrhocoricin which appear to deactivate a bacterial protein in a stereospecific manner. In accordance with their biological function, the membrane-active peptides form ordered structures, e.g. alpha-helices or beta-pleated sheets and often cast permeable ion-pores. Their cytotoxic properties were exploited in in vivo studies targeting tumour progression. Although the native peptides degrade quickly in biological fluids other than insect haemolymph, structural modifications render the peptides resistant against proteases without sacrificing biological activity. Indeed, a pyrrhocoricin analogue shows lack of toxicity in vitro and in vivo and protects mice against experimental Escherichia coli infection. Careful selection of lead molecules based on the insect antibacterial peptides may extend their utility and produce viable alternatives to the conventional antimicrobial compounds for mammalian therapy.

Mode of action of linear amphipathic alpha-helical antimicrobial peptides

The increasing resistance of bacteria to conventional antibiotics resulted in a strong effort to develop antimicrobial compounds with new mechanisms of action. Antimicrobial peptides seem to be a promising solution to this problem. Many studies aimed at understanding their mode of action were described in the past few years. The most studied group includes the linear, mostly alpha-helical peptides. Although the exact mechanism by which they kill bacteria is not clearly understood, it has been shown that peptide-lipid interactions leading to membrane permeation play a role in their activity. Membrane permeation by amphipathic alpha-helical peptides can proceed via either one of the two mechanisms: (a) transmembrane pore formation via a "barrel-stave" mechanism; and (b) membrane destruction/solubilization via a "carpet-like" mechanism. The purpose of this review is to summarize recent studies aimed at understanding the mode of action of linear alpha-helical antimicrobial peptides. This review, which is focused on magainins, cecropins, and dermaseptins as representatives of the amphipathic alpha-helical antimicrobial peptides, supports the carpet-like rather the barrel-stave mechanism. That these peptides vary with regard to their length, amino acid composition, and next positive charge, but act via a common mechanism, may imply that other linear antimicrobial peptides that share the same properties also share the same mechanism.

Characterisation of antibacterial activity of peptides isolated from the venom of the spider Cupiennius salei (Araneae: Ctenidae)

The characterisation of the antimicrobial activity of five antibacterial peptides, isolated from the venom of the neotropical wandering spider Cupiennius salei is reported here. The peptides have a molecular mass, determined by electrospray ionisation-mass spectrometry, between 3-4 kDa. Minimal inhibitory concentrations against five different bacteria species were determined by a liquid growth inhibition assay. All five peptides showed minimal inhibitory concentrations that are comparable to those of other known antibacterial peptides, like insect defensins and cecropins, found in the last years in a large diversity of animals. The peptides are supposed to lyse the cells by formation of either distinct channels or pores, but their mode of action is not yet revealed.

Antibacterial properties and partial cDNA sequences of cecropin-like antibacterial peptides from the common cutworm, Spodoptera litura

The antibacterial properties and cDNA sequences of two types of antibacterial peptides from the haemolymph of immunized common cutworm, Spodoptera litura larvae, were determined. Since the primary structures of peptides deduced from cDNA sequences showed significant homologies to cecropins A and B, they were named as Spodoptera cecropins A and B. Spodoptera cecropins were broadly effective against Gram-positive and negative bacteria. They also retained antibacterial activities in all conditions tested (at pH 5.6-8.0 and in the presence of 50-150 mM NaCl) that was adapted to confirm the antibacterial properties of Spodoptera cecropins. These results indicate that the change of pH and the increase of salt concentration in the media do not influence the activities of Spodoptera cecropins. For the reverse transcription (RT)-polymerase chain reaction (PCR) to obtain the complete primary sequence, the primer designed according to the conserved region of the cecropin leader sequences was used, which was determined by the comparison of the cDNA sequences of known cecropins. The results from RT-PCR presented that the partial cDNAs of Spodoptera cecropins A and B encode 57 and 58 amino acids, including the sequences of mature peptides, respectively. In addition, Northern blot analysis with (32)P-labeled PCR product coding for Spodoptera cecropin A revealed that Spodoptera cecropin genes are expressed in immunized fat body, but not in normal fat body.

Effects of the hinge region of cecropin A(1-8)-magainin 2(1-12), a synthetic antimicrobial peptide, on liposomes, bacterial and tumor cells

A 20-residue hybrid peptide (CA(1-8)-MA(1-12): KWKLFKKIGIGKFLHSAKKF-NH(2)) incorporating 1-8 residues of cecropin A (CA) and 1-12 residues of magainin 2 (MA) has potent antibiotic activity without hemolytic activity. In order to investigate the effects of the flexible hinge sequence, Gly-Ile-Gly of CA(1-8)-MA(1-12) (CA-MA) on antibiotic activity, CA-MA and its three analogues, CA-MA1, CA-MA2 and CA-MA3 were synthesized. The Gly-Ile-Gly sequence of CA-MA was deleted in CA-MA1 and replaced with Pro and Gly-Pro-Gly in CA-MA2 and CA-MA3, respectively. CA-MA1 and CA-MA3 caused a significant decrease in the bactericidal rate against Escherichia coli and Bacillus subtilis and the tumoricidal activity against four different tumor cells, and the PC/PS (4:1, w/w) vesicle-aggregating and disrupting activities. However, CA-MA2 showed a similar bactericidal rate and antitumor, vesicle-aggregating and disrupting activities, as compared with CA-MA. These results suggested that the flexibility or beta-turn induced by Gly-Ile-Gly or Pro in the central part of CA-MA may be important in the electrostatic interaction of the cationic short alpha-helical region in the N-terminus with the cell membrane surface and the hydrophobic interaction of amphipathic alpha-helical region in the C-terminus with the hydrophobic acyl chains in the cell membrane. CA-MA3 exhibited lower activity in antibacterial, antitumor, and vesicle-aggregating and disrupting activities than CA-MA and CA-MA2. This result suggested that the excessive beta-turn structure by Gly-Pro-Gly in CA-MA3 seems to interrupt the ion channel/pore formation on the lipid bilayer. It was concluded that the appropriate flexibility or beta-turn structure provided by the central hinge is responsible for the effective antibiotic activity of the antimicrobial peptides with the helix-hinge-helix structure.

Induction of mosquito hemolymph proteins in response to immune challenge and wounding

The rapid induction of proteins in the hemolymph of the mosquito, Anopheles gambiae, was examined after wounding or injection of immune elicitors (Escherichia coli, lipopolysaccharide, laminarin, zymosan). One-dimensional gel electrophoresis revealed at least six hemolymph polypeptides >25 kDa that consistently appeared after any breech of the cuticle. All of these polypeptides appeared in the hemolymph within 30 min and reached a maximum concentration after approx. 6 h. No proteins were specifically induced by bacteria or bacterial or fungal cell wall products, however two constitutively expressed proteins were repressed by these injections. Patterns of hemolymph proteins were further analyzed by two-dimensional electrophoresis. Seven spots were enhanced or induced 2 h after injection in four replicate experiments. An additional two spots demonstrated some variability between replicates, but were generally responsive to injection. These rapidly induced polypeptides are candidates for regulating and initiating the mosquito's responses to pathogens and wounding.

The terminal structure plays an important role in the biological activity of cecropin CMIV

Antibacterial peptides have received increasing attention as a new pharmaceutical substance. But the molecular mechanism of lysis is still poorly understood. CMIV gene and mutant CMIV gene in GST fusion system were expressed. After cleaving with different cleavage reagents, the peptide with an excess of N-terminus and with an un-amidated C-terminus stopped the activity while the peptide with an excess Asn at the C-terminus had the activity level the same as natural CMIV. The results showed that the terminal structure of cecropin CMIV played an important role in its biological activity.

Induction of carboxylesterase isozymes in Bombyx mori by E. coli infection

Many proteins, including antibacterial peptides in the hemolymph, are induced by bacterial infections. We found two bacterially inducible carboxylesterases (CEs) in the hemolymph of the silkworm, Bombyx mori. CEs Est-1 and 2 were induced by lipopolysaccharide injection after 6 hours as well as E. coli infection. We found that bacterially inducible CEs clearly differed from noninducible CEs, including juvenile hormone esterases, in pI values, migration on analytical native PAGE, and inhibitor sensitivity. We are now studying the features and functions of these CEs.

Antibiotic peptides from higher eukaryotes: biology and applications

Gene-encoded antibiotic peptides are increasingly being recognized as effector molecules of host defense in plants and animals. Studies of antimicrobial peptides are providing new insights into the dynamic interactions between microbes and their hosts, and are generating new paradigms for the pathogenesis and treatment of diseases. Because antimicrobial peptides of higher eukaryotes differ structurally from conventional antibiotics produced by bacteria and fungi, they offer novel templates for pharmaceutical compounds that could be effective against increasingly resistant microbes.

Insect immunity: molecular cloning, expression, and characterization of cDNAs and genomic DNA encoding three isoforms of insect defensin in Aedes aegypti

Aedes aegypti were immune activated by injection with bacteria, and the expression of insect defensins was measured over time. Northern analyses indicated that defensin transcriptional activity continued for at least 21 days after bacterial injection, and up to 10 days after saline inoculation. Mature defensin levels in the haemolymph reached approximately 45 microM at 24 h post inoculation. cDNAs encoding the preprodefensins of three previously described mature Ae. aegypti defensins were amplified by PCR, cloned and sequenced. Genomic clones were amplified using primers designed against the cDNA sequence. Sequence comparison indicates that there is significant inter- and intra-isoform variability in the signal peptide and prodefensin sequences of defensin genes. Preprodefensin sequences of isoforms A and B are very similar, consisting of a signal peptide region of twenty amino acids, a prodefensin region of thirty-eight amino acids and a forty amino acid mature peptide domain. The sequence encoding isoform C is significantly different, comprising a signal peptide region of twenty-three amino acids, a prodefensin region of thirty-six amino acids, and the mature protein domain of forty amino acids. Analysis of the genomic clones of each isoform revealed one intron spatially conserved in the prodefensin region of all sequences. The intron in isoforms A and B is 64 nt long, and except for a 4 nt substitution in one clone, these intron sequences are identical. The intron in isoform C is 76 nt long and does not share significant identity with the intron sequences of isoforms A or B. The defensin gene mapped to chromosome 3, between two known loci, blt and LF168.

Tsetse thrombin inhibitor: bloodmeal-induced expression of an anticoagulant in salivary glands and gut tissue of Glossina morsitans morsitans

The tsetse thrombin inhibitor, a potent and specific low molecular mass (3,530 Da) anticoagulant peptide, was purified previously from salivary gland extracts of Glossina morsitans morsitans (Diptera: Glossinidae). A 303-bp coding sequence corresponding to the inhibitor has now been isolated from a tsetse salivary gland cDNA library by using degenerate oligonucleotide probes. The full-length cDNA contains a 26-bp untranslated segment at its 5' end, followed by a 63-bp sequence corresponding to a putative secretory signal peptide. A 96-bp segment codes for the mature tsetse thrombin inhibitor, whose predicted molecular weight matches that of the purified native protein. Based on its lack of homology to any previously described family of molecules, the tsetse thrombin inhibitor appears to represent a unique class of naturally occurring protease inhibitors. Recombinant tsetse thrombin inhibitor expressed in Escherichia coli and the chemically synthesized peptide are both substantially less active than the purified native protein, suggesting that posttranslational modification(s) may be necessary for optimal inhibitory activity. The tsetse thrombin inhibitor gene, which is present as a single copy in the tsetse genome, is expressed at high levels in salivary glands and midguts of adult tsetse flies, suggesting a possible role for the anticoagulant in both feeding and processing of the bloodmeal.

Lumbricin I, a novel proline-rich antimicrobial peptide from the earthworm: purification, cDNA cloning and molecular characterization

A novel antimicrobial peptide was isolated and characterized from the earthworm, Lumbricus rubellus. The antimicrobial peptide was purified to homogeneity by a heparin-affinity column and C18 reverse-phase HPLC, and named lumbricin I. Lumbricin I was a proline-rich antimicrobial peptide of 62 amino acids (15% proline in molar ratio; molecular mass, 7231 Da), whose complete sequence was determined by a combination of peptide sequence and cDNA analysis. The peptide and cDNA sequence analysis revealed that lumbricin I was produced as a precursor form consisting of 76 amino acids, with 14 residues in a presegment and 62 residues in mature lumbricin I. Lumbricin I showed antimicrobial activity in vitro against a broad spectrum of microorganisms without hemolytic activity. In addition, a 29-amino acid peptide, named lumbricin I(6-34), which was derived from residues 6-34 of lumbricin I, showed marginally stronger antimicrobial activity than lumbricin I. Northern blot analysis on total RNA revealed that expression of lumbricin I gene was not induced by bacterial infection, but was constitutively expressed. Furthermore, the expression of lumbricin I gene was specific in adult L. rubellus: Lumbricin I mRNA was detected only in adult L. rubellus, but not in eggs and young L. rubellus.

Secondary structure of an antibacterial peptide Abp3 studied by two-dimensional proton-NMR

An antibacterial peptide Abp3, an analogue of cecropin B, was investigated by two-dimensional proton-NMR at pH 5.0 in aqueous solution with 15% (v/v) hexafluoroisopropanol. The peptide, which consists of 35 amino acids, was synthesized chemically. Most resonances of the main-chain and side-chain protons were assigned. Several medium range NOE connectivities were observed, showing two separate alpha-helices with one amphiphilic in N-terminal domain (residues 5-21) and the other hydrophobic in C-terminal domain (residues 25-35) and a hinge region between them. The J coupling constants and the chemical shifts in these sections also supported the conclusion.

Cloning and expression of a novel gene encoding a new antibacterial peptide from silkworm, Bombyx mori

We differentially screened a novel gene encoding a new antibacterial peptide from the immunized Bombyx mori cDNA library. The gene showed a similar structure to that of cecropin-family, encoding 59 amino acids including a putative leader peptide and mature peptide. The deduced peptide, named Enbocin, had conserved amino acid residues which have been known to play an important role in the antibacterial activities. Enbocin genomic sequence revealed that the transcription unit of Enbocin gene was about 1.2 kb, and the coding sequence was interrupted by an intron of 660 bases. Recombinant Enbocin, expressed under the control of the baculovirus polyhedrin promoter, demonstrated a broad range of antibacterial activities against gram positive and gram negative bacteria.

Purification of pierisin, an inducer of apoptosis in human gastric carcinoma cells, from cabbage butterfly, Pieris rapae

A substance strongly cytotoxic to human carcinoma cell line TMK-1 has been found in pupae, larvae and adults of the cabbage butterfly, Pieris rapae, and named pierisin. Pierisin was purified from the pupae of P. rapae by ammonium sulfate precipitation followed by DEAE-cellulose, Phenyl-Sepharose and hydroxyapatite column chromatographies. The molecular weight of the purified pierisin, which was homogenous on SDS-polyacrylamide gel, was analyzed by mass spectrometry and found to be 98 kDa. Pierisin showed a strong cytotoxic effect, with and IC50 of 0.75 ng/ml for human gastric carcinoma TMK-1 cells. The dying cells exhibited characteristic morphological features of apoptosis, such as cell shrinkage, chromatin condensation and nuclear fragmentation. Oligonucleosomal DNA fragmentation was also observed in DNA isolated from pierisin-treated cells. Moreover, similar characteristic changes showing apoptotic cell death were observed in TMK-1 cells treated with a crude extract of pupae of P. rapae. These results indicate that pierisin from the pupae of P. rapae induces apoptosis in human carcinoma cells.

A novel lectin from Sarcophaga. Its purification, characterization, and cDNA cloning

A novel C-type lectin that agglutinates rabbit red cells was purified from NIH-Sape-4 cells derived from the flesh fly (Sarcophaga peregrina), and its cDNA was isolated. This lectin, named granulocytin, appeared to be a trimer of a 20-kDa subunit consisting of 151 amino acid residues. The gene for granulocytin was activated in third instar larvae, and its expression was enhanced when the larval body wall was injured. In third instar larvae, granulocytin was found to be synthesized by hemocytes and secreted into the hemolymph. The molecular mass and gene expression patterns of granulocytin were very similar to those of Drosophila lectin that we reported previously (Haq, S., Kubo, T., Kurata, S., Kobayashi, A., and Natori, S. (1996) J. Biol. Chem. 271, 20213-20218). However, these two lectins showed amino acid identities of 20% at most, and no significant hapten sugar for granulocytin was identified.