Molecular cloning of a putative homolog of proline/arginine-rich antibacterial peptides from porcine bone marrow

Effect of recombinant prophenin 2 on the integrity and viability of Trichomonas vaginalis

Trichomonas vaginalis is the causal agent of trichomoniasis, which is associated with preterm child delivery, low birth weight, and an increased risk of infection by human papilloma virus and human immunodeficiency virus following exposure. Several reports have established increasing numbers of trichomoniasis cases resistant to metronidazole, the agent used for treatment, and it is therefore important to identify new therapeutic alternatives. Previously, our group reported the effect of tritrpticin, a synthetic peptide derived from porcine prophenin, on T. vaginalis; however, the hemolytic activity of this small peptide complicates its possible use as a therapeutic agent. In this study, we report that the propeptide and the processed peptide of prophenin 2 (cleaved with hydroxylamine) affected the integrity and growth of T. vaginalis and that pro-prophenin 2 displays some resistance to proteolysis by T. vaginalis proteinases at 1 h. Its effect on T. vaginalis as well as its low hemolytic activity and short-time stability to parasite proteinases makes prophenin 2 an interesting candidate for synergistic or alternative treatment against T. vaginalis.

[Progress in cathelicidins antimicrobial peptides research]

Cathelicidins are a family of multi-functional antimicrobial peptides found in almost all types of vertebrates, where they play vital roles in the immune system. As they possess broad-spectrum antimicrobial properties, cathelicidins are not only strongly resistant to Gram-positive and Gram-negative bacteria, fungi, and viruses, but they are also active against many antibiotic-resistant clinical bacteria, adopting a special antimicrobial mechanism that is unlikely to lead to microbial resistance. Cathelicidins likewise possess simple structures, and low hemolytic and cytotoxic activities. Collectively, these features suggest potentially novel and exciting prospects for cathelicidins' application in medicine. Here, we review the structures, classification, activities, mechanisms, as well as prospective developments in the usage and application of cathelicidin antimicrobial peptides.

Proline-rich antimicrobial peptides: converging to a non-lytic mechanism of action

Proline-rich antimicrobial peptides are a group of cationic host defense peptides of vertebrates and invertebrates characterized by a high content of proline residues, often associated with arginine residues in repeated motifs. Those isolated from some mammalian and insect species, although not evolutionarily related, use a similar mechanism to selectively kill Gram-negative bacteria, with a low toxicity to animals. Unlike other types of antimicrobial peptides, their mode of action does not involve the lysis of bacterial membranes but entails penetration into susceptible cells, where they then act intracellularly. Some aspects of the transport system and cytoplasmic targets have been elucidated. These features make them attractive both as anti-infective lead compounds and as a new class of potential cell-penetrating peptides capable of internalising membrane-impermeant drugs into both bacterial and eukaryotic cells.

Effect of the antimicrobial peptide tritrpticin on the in vitro viability and growth of Trichomonas vaginalis

Antimicrobial peptides are widely distributed in nature; they play important roles in several aspects of innate immunity and may provide a basis for the design of novel therapeutic agents. In this study, C-amidated tritrpticin, a 13 amino acid tryptophan-rich antimicrobial peptide derived from a porcine cathelicidin, was tested against Trichomonas vaginalis, a protozoan that causes a serious non-viral sexually transmitted disease associated with preterm birth, low birth weight, and high risk of HIV-1 infection. Tritrpticin was selected due to its reasonably easy synthesis and because analogs with lower toxicity may be designed. Our results show that tritrpticin-NH(2) at either 100 or 200 μg/ml (52.5 or 105 μM) clearly reduces the viability and growth of Trichomonas vaginalis. Together with tritrpticin-NH(2), sodium bicarbonate further limited trichomonad growth. Additionally, a low concentration of metronidazole (5.8 μM), the most commonly used medication for Trichomonas vaginalis, was more effective against the growth of the parasite when it was combined with tritrpticin-NH(2).

Structure-function analysis of tritrpticin analogs: potential relationships between antimicrobial activities, model membrane interactions, and their micelle-bound NMR structures

Tritrpticin is a member of the cathelicidin family of antimicrobial peptides. Starting from its native sequence (VRRFPWWWPFLRR), eight synthetic peptide analogs were studied to investigate the roles of specific residues in its biological and structural properties. This included amidation of the C-terminus paired with substitutions of its cationic and Phe residues, as well as the Pro residues that are important for its two-turn micelle-bound structure. These analogs were determined to have a significant antimicrobial potency. In contrast, two other peptide analogs, those with the three Trp residues substituted with either Phe or Tyr residues are not highly membrane perturbing, as determined by leakage and flip-flop assays using fluorescence spectroscopy. Nevertheless the Phe analog has a high activity; this suggests an intracellular mechanism for antimicrobial activity that may be part of the overall mechanism of action of native tritrpticin as a complement to membrane perturbation. NMR experiments of these two Trp-substituted peptides showed the presence of multiple conformers. The structures of the six remaining Trp-containing analogs bound to dodecylphosphocholine micelles showed major, well-defined conformations. These peptides are membrane disruptive and show a wide range in hemolytic activity. Their micelle-bound structures either retain the typical turn-turn structure of native tritrpticin or have an extended alpha-helix. This work demonstrates that closely related antimicrobial peptides can often have remarkably altered properties with complex influences on their biological activities.

Hagfish intestinal antimicrobial peptides are ancient cathelicidins

Three potent broad-spectrum antimicrobial peptides (HFIAP-1, -2, and -3) isolated from intestinal tissues of Myxine glutinosa (Atlantic hagfish) are identified as ancient members of the cathelicidin family of antimicrobial peptides, hitherto known only from mammals. In situ hybridization reveals that HFIAPs are produced in nests of myeloid cells within the loose connective tissue of the gut wall, a tissue reminiscent of both gut-associated lymphoid tissue (GALT) and vertebrate spleen. We suggest that this tissue organization provides local defense of the hagfish gastrointestinal tract via innate immunity and possibly served as the architectural plan upon which the adaptive immune system evolved.

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.

RL-37, an alpha-helical antimicrobial peptide of the rhesus monkey

Rhesus monkey bone marrow expresses a cathelicidin whose C-terminal domain comprises a 37-residue alpha-helical peptide (RL-37) that resembles human LL-37. Like its human counterpart, RL-37 rapidly permeabilized the membranes of Escherichia coli ML-35p and lysed liposomes that simulated bacterial membranes. When tested in media whose NaCl concentrations approximated those of extracellular fluids, RL-37 was considerably more active than LL-37 against staphylococci. Whereas human LL-37 contains five acidic residues and has a net charge of +6, rhesus RL-37 has only two acidic residues and a net charge of +8. Speculating that the multiple acidic residues of human LL-37 reduced its efficacy against staphylococci, we made a peptide (LL-37 pentamide) in which each aspartic acid of LL-37 was replaced by an asparagine and each glutamic acid was replaced by a glutamine. LL-37 pentamide's antistaphylococcal activity was substantially greater than that of LL-37. Thus, although the precursor of LL-37 is induced in human skin keratinocytes by injury or inflammation, its insufficiently cationic antimicrobial domain may contribute to the success of staphylococci in colonizing and infecting human skin.

Structural features and biological activities of the cathelicidin-derived antimicrobial peptides

Cathelicidins are a numerous group of mammalian proteins that carry diverse antimicrobial peptides at the C-terminus of a highly conserved preproregion. These peptides, which become active when released from the proregion, display a remarkable variety of sizes, sequences, and structures, and in fact comprise representatives of all the structural groups in which the known antimicrobial peptides have been classified. Most of the cathelicidin-derived peptides exert a broad spectrum and potent antimicrobial activity and also bind to lipopolysaccharide and neutralize its effects. In addition, some of them have recently been shown to exert other activities and might participate in host defense also by virtue of their ability to induce expression of molecules involved in a variety of biological processes. This review is aimed at providing a general overview of the cathelicidins and of the peptides derived therefrom, with emphasis on aspects such as structure, biological activities in vitro and in vivo, and structure/activity relationship studies.

Characterisation of variant forms of prophenin: mechanistic aspects of the fragmentation of proline-rich peptides

Prophenin 1 (PF-1) is a 79-residue polypeptide originally isolated from porcine leukocytes. Its amino acid sequence has been determined by a combination of mass spectrometry and Edman degradation (Harwig SSL. et al. FEBS Lett. 1995; 362: 65). Prophenin (PF) and variants thereof are also found in organic extracts of porcine pulmonary tissue (Wang Y. et al. FEBS Lett. 1999; 460: 257). In the present study we have characterised the variant forms of PF found in these extracts using nano-electrospray (nano-ES) high resolution and tandem mass spectrometry. The major forms of PF found in these extracts by nano-ES mass spectrometry are the 80-residue polypeptides prophenin-2-Pyr (PF-2-Pyr) and prophenin-2-Gln (PF-2-Gln). Prophenin-2-Pyr is refractory to Edman degradation due to the presence of an N-terminal pyroglutamic residue. In PF-2-Gln the N-terminal residue is glutamine and the C-terminus is amidated. In porcine pulmonary extracts PF-1 is present to only a minor extent. Other shorter polypeptides are also found in these extracts including 18- and 17-residue C-terminal fragments of PF. The primary structure of PF is highly unusual in that it shows four almost perfect decamer repeats of FPPPN(V/F)PGPR and, out of the 79/80 residues, 42 are proline and 14 are phenylalanine. Tryptic digestion of PF gives peptides containing the decamer repeat and collision-induced dissociation of these peptides provides an insight into the fragmentation mechanisms of proline-rich peptides. Facile cleavage within the Pro-Pro-Pro sequence of these peptides suggests the involvement of a cyclic peptide in the fragmentation mechanism. Fragmentation mechanisms that account for the formation of fragment ions at other cleavage sites are also discussed.

Structure of the antimicrobial peptide tritrpticin bound to micelles: a distinct membrane-bound peptide fold

Tritrpticin is a member of the cathelicidin family, a group of diverse antimicrobial peptides found in neutrophil granules. The three Trp and four Arg residues in the sequence VRRFPWWWPFLRR make this a Trp-rich cationic peptide. The structure of tritrpticin bound to membrane-mimetic sodium dodecyl sulfate micelles has been determined using conventional two-dimensional NMR methods. It forms two adjacent turns around the two Pro residues, a distinct fold for peptide-membrane interaction. The first turn involves residues 4-7, followed immediately by a second well-defined 3(10)-helical turn involving residues 8-11. The hydrophobic residues are clustered together and are clearly separated from the basic Arg residues, resulting in an amphipathic structure. Favorable interactions between the unusual amphipathic fold and the micelle surface are probably key to determining the peptide structure. NMR studies of the peptide in the micelle in the presence of the spin-label 5-doxylstearic acid determined that tritrpticin lies near the surface of the micelle, where its many aromatic side chains appear to be equally partitioned into the hydrophilic-hydrophobic interface. Additional fluorescence studies confirmed that the tryptophan residues are inserted into the micelle and are partially protected from the effects of the soluble fluorescence quencher acrylamide.

Porcine pulmonary surfactant preparations contain the antibacterial peptide prophenin and a C-terminal 18-residue fragment thereof

Surfactant preparations obtained from porcine lungs by extraction with chloroform/methanol followed by chromatography over Lipidex-5000 are used for treatment of respiratory distress syndrome in preterm infants. These preparations contain about 98% phospholipids and 1-2% of the hydrophobic pulmonary surfactant-associated proteins B and C (SP-B and SP-C). Separation of the proteins in the surfactant preparation by reversed-phase high performance liquid chromatography revealed, in addition to SP-B and SP-C, the presence of three peptides derived from the cathelicidin family of antibacterial peptides. The 79-residue proline-rich peptide prophenin (identical to that isolated from leukocytes), an 80-residue prophenin with an N-terminal pyroglutamic acid residue, and a C-terminal 18-residue fragment of prophenin were found in approximate molar ratios of 1:20:5. A synthetic version of the C-terminal 18-residue peptide exhibits salt-dependent antibacterial activity (higher activity in the absence of salt) against the Gram-positive bacterium Bacillus megaterium Bm11 and, to a lesser extent, against Gram-negative Escherichia coli D21 cells. It appears possible that the presence of prophenin peptides may contribute to the antibacterial properties of surfactant preparations.

Effects of tryptophan residues of porcine myeloid antibacterial peptide PMAP-23 on antibiotic activity

PMAP-23 is a 23-residue antimicrobial peptide from porcine myeloid cells. In order to determine the effects of two Trp residues in positions 7 and 21 of PMAP-23 on antibacterial activity and phospholipid vesicle interacting property, two analogues in which Ala is substituted for Trp residue in position 7 or 21 were synthesized. A(21)-PMAP-23 exhibited reduced antibacterial activity and phospholipid vesicle disrupting activity when compared to those of PMAP-23 and A(7)-PMAP-23. PMAP-23 readily interacted with model lipid membrane and induced membrane destabilization. Therefore antibacterial activity induced by PMAP-23 is due to the interaction of cell membrane with peptide followed by membrane perturbation. A significant structural change on the SDS micelle was not found by Ala substitution of the Trp residue of PMAP-23. Also, there is a good correlation between hydrophobic interaction on RP-HPLC, expressed as retention time on RP-HPLC, and antibacterial activity. The vesicle titration experiment indicated that Trp residues located at near C-terminus are accessible to hydrophobic tail of phospholipid vesicle. This result suggests that the C-terminal end of PMAP-23 penetrates into the lipid bilayer in the course of the interaction with phospholipid membranes and is important for its antibacterial activity.

Structure-function analysis of tritrypticin, an antibacterial peptide of innate immune origin

The structural requirements for the antibacterial activity of a pseudosymmetric 13-residue peptide, tritrypticin, were analyzed by combining pattern recognition in protein structures, the structure-activity knowledge-base, and circular dichroism. The structure-activity analysis, based on various deletion analogs, led to the identification of two minimal functional peptides, which by themselves exhibit adequate antibacterial activity against Escherichia coli and Salmonella typhimurium. The common features between these two peptides are that they both share an aromatic-proline-aromatic (ArProAr) sequence motif, and their sequences are retro with respect to one another. The pattern searches in protein structure data base using the ArProAr motif led to the identification of two distinct conformational clusters, namely polyproline type II and beta-turn, which correspond to the observed solution structures of the two minimal functional analogs. The role of different residues in structure and function of tritrypticin was delineated by analyzing antibacterial activity and circular dichroism spectra of various designed analogs. Three main results arise from this study. First, the ArProAr sequence motif in proteins has definitive conformational features associated with it. Second, the two minimal bioactive domains of tritrypticin have entirely different structures while having equivalent activities. Third, tritrypticin has a beta-turn conformation in solution, but the functionally relevant conformation of this gene-encoded peptide antibiotic may be an extended polyproline type II.

Antimicrobial peptides as mediators of epithelial host defense

Mammalian epithelial surfaces are remarkable for their ability to provide critical physiologic functions in the face of frequent microbial challenges. The fact that these mucosal surfaces remain infection-free in the normal host suggests that highly effective mechanisms of host defense have evolved to protect these environmentally exposed tissues. Throughout the animal and plant kingdoms, endogenous genetically encoded antimicrobial peptides have been shown to be key elements in the response to epithelial compromise and microbial invasion. In mammals, a variety of such peptides have been identified, including the well-characterized defensins and cathelicidins. A major source of these host defense molecules is circulating phagocytic leukocytes. However, more recently, it has been shown that resident epithelial cells of the skin and respiratory, alimentary, and genitourinary tracts also synthesize and release antimicrobial peptides. Both in vitro and in vivo data support the hypothesis that these molecules are important contributors to intrinsic mucosal immunity. Alterations in their level of expression or biologic activity can predispose the organism to microbial infection. The regulatory and developmental aspects of antimicrobial peptide synthesis are discussed from a perspective that emphasizes the possible relevance to pediatric medicine.

Macrophage-dependent regulation of syndecan gene expression

Heparan sulfates in the extracellular matrix are required for a variety of biological processes, including cellular response to heparin-binding growth factors. However, little is known regarding the regulation of their expression and composition under pathophysiological conditions. In the present study, we have investigated the regulation of expression of two key heparan sulfate chain-carrying core proteins, syndecan-1 and syndecan-4, in a mouse/rat infarct model of tissue injury and repair. Induction of myocardial infarction was associated with a prompt increase in expression of both syndecan genes. Although infiltrating macrophages accounted for a substantial increase in syndecan expression, increased expression was noted in the levels of syndecan-1 mRNA in endothelial cells and syndecan-4 mRNA in cardiac myocytes. This increase in expression was limited to the immediate peri-infarct region and was absent from remote areas of the left or right ventricles. The influx of blood-derived macrophages in the heart correlated with the appearance of PR-39 peptide, which has previously been shown to increase syndecan expression in vitro. Studies in the op/op mice strain (which demonstrates sharply reduced levels of circulating monocytes) showed that myocardial infarction was associated with markedly reduced levels of macrophage influx and corresponding reduction in the expression of PR-39 and both syndecan genes. Pretreatment of op/op mice with granulocyte macrophage colony-stimulating factor restored myocardial macrophage content with corresponding restoration of PR-39/syndecan expression. In summary, myocardial infarction is associated with a distinct spatial and temporal pattern of syndecan-1 and -4 gene expression, which is induced by an influx of blood-derived macrophages.

Isolation of cDNA encoding guinea pig neutrophil cationic antibacterial polypeptide of 11 kDa (CAP11) and evaluation of CAP11 mRNA expression during neutrophil maturation

Neutrophils contain various antibacterial polypeptides and proteins in the granules that contribute to the killing of microorganisms. Recently, we have purified a cationic antibacterial polypeptide of 11 kDa (CAP11) from guinea pig neutrophil granules. CAP11 is a homodimer of G1LRKKFRKTRKRIQKLGRKIGKTGRKVWKAWREYGQIPYPCRI43 joined with one disulfide bond. In this study, to understand the regulation of CAP11 expression, we isolated and analyzed cDNA encoding CAP11. Furthermore, we investigated the expression of CAP11 mRNA during neutrophil maturation and localization of CAP11 among neutrophil granule subsets. Sequence analysis of CAP11 cDNA isolated from guinea pig bone marrow cells using rapid amplification of cDNA ends technique indicated that CAP11 is synthesized as a precursor comprising 178 amino acid residues, which is composed of a signal peptide (N-terminal 29 residues), a propeptide (106 residues), and a C-terminal mature peptide (43 residues). Interestingly, the predicted CAP11 precursor displayed the characteristic features of cathelicidins, a novel protein family of antibacterial polypeptides with a conserved cathelin-like pro-region and a variable C-terminal antibacterial domain. Northern blot and Western blot analyses using neutrophils, macrophages, eosinophils, mononuclear cells, and bone marrow cells revealed that only neutrophils and bone marrow cells expressed CAP11 mRNA and contained CAP11, suggesting that expression of CAP11 is neutrophil lineage-specific. Furthermore, Northern blot analysis using bone marrow cells separated according to their maturation stages showed that CAP11 mRNA was predominantly expressed in the cells at later stages of neutrophil maturation. Consistent with this, in situ hybridization using CAP11-specific cRNA probe demonstrated that CAP11 mRNA was primarily expressed at metamyelocyte stage. In addition, extracellular release assay revealed that CAP11 was readily released from neutrophils accompanied with gelatinase by low concentrations of N-formyl-Met-Leu-Phe without release of specific and azurophil granule components, and CAP11 was found to be exclusively present in the fraction containing gelatinase granules, prepared by Percoll density gradient centrifugation. Together these observations indicate that CAP11 is a member of cathelicidin family and its mRNA is preferentially expressed at the later stage of neutrophil maturation (i.e. metamyelocyte stage). Furthermore, CAP11 may be stored in the granule subset, possibly the gelatinase granule.

Structural, functional analysis and localization of the human CAP18 gene

CAP18 is an antimicrobial protein found in specific granules of PMNs. The human CAP18 (HCAP18) gene was cloned from a human genomic phage library. Sequence analysis revealed the HCAP18 gene to have 4 exons spanning 3 kb, including 700 bp of upstream DNA. Using 3' RACE no homologs of human HCAP18 were found in human bone marrow or leukocyte populations. By PCR analysis of a somatic cell mapping panel and fluorescence in situ hybridization of a genomic clone to metaphase chromosomes the gene was mapped to chromosome band 3p21.3. Like several other genes expressed late in PMN development the CAP18 gene did not contain typical TATA box or CCAAT sequences. Expression in Cos 7 cells permitted limited mapping of the promoter function in upstream fragments of the HCAP18 gene. Western blot, Northern blot and RT-PCR analysis show HCAP18 to be produced specifically in granulocytes. This work forms the groundwork for future analysis of the genetic regulation of this antimicrobial protein during PMN differentiation.

Biological characterization of two novel cathelicidin-derived peptides and identification of structural requirements for their antimicrobial and cell lytic activities

Cathelicidins are a family of myeloid antimicrobial peptide precursors that have been identified in several mammalian species (Zanetti, M., Gennaro, R., and Romeo, D. (1995) FEBS Lett. 374, 1-5). Two novel bovine congeners have been deduced from cDNA. Their C-terminal sequences of 27 and 28 residues correspond to putative antimicrobial peptides with a cationic N-terminal region predicted to assume an amphipathic alpha-helical conformation followed by a hydrophobic C-terminal tail. Peptides corresponding to these sequences have been chemically synthesized and shown to exert a potent antimicrobial activity against Gram-negative and Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus, and fungi. Both peptides are also cytotoxic to human erythrocytes and neutrophils, although at higher than microbicidal concentrations. The target selectivity has been improved by synthesizing truncated analogues, comprising only the 18 N-terminal residues, which show a great reduction in cytotoxic, but not in antimicrobial activity. The involvement of the C-terminal hydrophobic tail in the cytotoxic activity has been further demonstrated by inducing a major loss of activity in an analogue after replacing highly hydrophobic residues with more hydrophilic ones.

Antimicrobial activity of a 13 amino acid tryptophan-rich peptide derived from a putative porcine precursor protein of a novel family of antibacterial peptides

It has long been speculated that porcine cathelin is an N-terminal fragment of a longer precursor protein which possesses antimicrobial activity. In an attempt to find such a precursor, a cDNA clone was recently isolated and sequenced by screening a cDNA library from porcine bone marrow. In order to identify the functional activity of the putative protein encoded by an open reading frame, we have synthesized various lengths of peptides that correspond to the C-terminal region of the protein and examined them for their antimicrobial activities. We found that a 13 amino acid tryptophan-rich region with the sequence of VRRFPWWWPFLRR had strong antimicrobial activity with a wide spectrum. It showed potency against Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumonia, Staphylococcus epidermidis, Proteus mirabilis, and Streptococcus group D as well as Aspergillus fumigatus. The action of this peptide is bactericidal rather than bacteriostatic and this activity is completely inhibited by 2 mM MgCl2. Our results indicate that the previously identified putative precursor encoded by the isolated cDNA indeed possesses a potent antimicrobial activity and that this 13 amino acid synthetic peptide is considered to be a potentially effective drug against various infectious agents.

Purification and structural characterization of bovine cathelicidins, precursors of antimicrobial peptides

Cathelicidins are a novel family of antimicrobial peptide precursors from mammalian myeloid cells. They are characterized by a conserved N-terminal region while the C-terminal antimicrobial domain can vary considerably in both primary sequence and length. Four cathelicidins, proBac5, proBac7, prododecapeptide and proBMAP-28, have been concurrently purified from bovine neutrophils, using simple and rapid methodologies. The correlation of ES-MS data from the purified proteins with their cDNA-deduced sequences has revealed several common features of their primary sequence, such as the presence of N-terminal 5-oxoproline (pyroglutamate) residues and two disulfide bridges in a 1-2, 3-4 arrangement. The N-terminal domains of the cathelicidins present one or two Asp-Pro bonds, which are particularly acid-labile in proBac5 and proBac7, but stable in prododecapeptide. This suggests that the spatial organization around these bonds may vary in different cathelicidins, and favour hydrolysis in some cases. An unexpected feature of the prododecapeptide is that it exists as dimers formed by three possible combinations of its two isoforms. The isolation of a truncated, monomeric form of this protein, lacking the cysteine-containing antimicrobial dodecapeptide, indicates that dimerization occurs via disulfide bridge formation at the level of the C-terminal domain and that the dodecapeptide is likely released as a dimer from its precursor. Sequence-based secondary structure predictions and CD results indicate for cathelicidins a 30-50% content of extended conformation and <20% content of alpha-helical conformation, with the alpha-helical segment placed near the N-terminus. Finally, similarity searching and topology-based structure prediction underline a significant sequential and structural similarity between the conserved N-terminal domain of cathelicidins and cystatin-like domains, placing this family within the cystatin superfamily. When assayed against cathepsin L, unlike the potent cystatin inhibitors, three of the four cathelicidins show only a poor inhibitory activity (Ki = 0.6-3 microM).

cDNA sequences of three sheep myeloid cathelicidins

Several myeloid antimicrobial peptide precursors have been shown to consist of a N-terminal proregion similar to a protein named cathelin and a structurally varied C-terminal antimicrobial domain. Proteins with these features have been named cathelicidins. In this paper we report the cDNA sequences of three ovine cathelicidins of 155, 160 and 190 residues, respectively, with cationic C-terminal sequences corresponding to putative antimicrobial domains. These are structurally varied and include a Cys-rich sequence of 12 residues, which is similar to the bovine antimicrobial cyclic dodecapeptide, a novel 29 residue sequence named SMAP-29 with a possible alpha-helical conformation, and a 60 residue sequence named Bac7.5, which appears to be a new member of the Pro- and Arg-rich group of mammalian antimicrobial peptides.

Structures of genes for two cathelin-associated antimicrobial peptides: prophenin-2 and PR-39

We characterized genes for prophenin (PF)-2 and PR-39, two cathelin-associated antimicrobial peptides found in porcine leukocytes. Both contained 4 exons and 3 introns and were compact, contiguous and highly homologous. Exons I-III encoded most of their cathelin domains. Exon IV specified the final few cathelin residues, including its conserved C-terminal valine, followed by the mature PR-39 peptide or a PF-2 precursor. The highly conserved 5' flanking sequences of this gene family contained NF-kappa B, IL-6, GM-CSF and NF-1 binding motifs and the introns were unusually conserved. These data suggest that the panoply of porcine cathelin-associated antimicrobial peptides arose relatively recently via gene reduplications and exon shuffling, and that in vivo expression of cathelin-associated antimicrobial peptides may respond to mediators generated early during infection.

Cathelicidins: a novel protein family with a common proregion and a variable C-terminal antimicrobial domain

A novel protein family, showing a conserved proregion and a variable C-terminal antimicrobial domain, and named cathelicidin, has been identified in mammalian myeloid cells. The conserved proregion shows sequence similarity to members of the cystatin superfamily of cysteine proteinase inhibitors. Cathelicidins are stored in the cytoplasmic granules of neutrophil leukocytes and release the antimicrobial peptides upon leukocyte activation. Some of these peptides can assume an alpha-helical conformation, others contain one or two disulfide bonds, still others are Pro- and Arg-rich, or Trp-rich. In addition to bacterial killing, some of these peptides exert additional functions related to host defense such as LPS-neutralization and promotion of wound healing.

Molecular cloning and identification of a novel porcine cathelin-like antibacterial peptide precursor

A novel clone (C6) encoding the precursor of a 79-residue proline/arginine-rich antibacterial peptide prophenin was isolated from a porcine bone marrow cDNA library. Its deduced N-terminal propart shows 84% identity with cathelin. Additionally, two cathelin isoforms were isolated from peripheral porcine blood and their N-termini sequenced. The sequence of one isoform corresponds to the cathelin sequence, whereas that of the other protein is identical to the propeptide of C6 clone. Western blot analysis of total proteins from porcine and human bone marrow using polyclonal antibodies against cathelin revealed the presence of immunochemically related high molecular mass proteins of about 30 kDa in both samples, whereas low molecular mass proteins of approximately 12 kDa, corresponding to isolated cathelin, were not detected in human bone marrow.

The structure of porcine protegrin genes

We cloned the genes of three protegrins, a family of cathelin-associated antimicrobial peptides originally isolated from porcine leukocytes. Each gene comprised 4 exons and 3 introns, wherein Exon I encoded the signal sequence and the first 37 amino acids of cathelin, Exons II and III contained 36 and 24 additional cathelin residues and Exon IV contained the final two cathelin residues followed by the protegrin sequence. This quadripartite gene structure helps explain how structurally diverse antimicrobial peptides can be expressed on common, cathelin-containing precursors. Southern blot probed with an oligonucleotide specific for protegrin genes suggested that several identical or nearly identical protegrin genes were densely clustered in the pig chromosome.

hCAP-18, a cathelin/pro-bactenecin-like protein of human neutrophil specific granules

A 19 kDa protein was identified in specific granules of human neutrophils. A full-length cDNA clone was isolated from a human CML cDNA library, based on amino-acid sequences of isolated tryptic fragments. This clone includes the recently identified cDNA for FALL-39/CAP-18. Aminoacid sequences of proteolytic fragments derived both from the conserved N-terminal cathelin-like region and the highly variable C-terminal region characteristic of this family of bactericidal, LPS binding proteins, were in complete agreement with the sequence deduced from the cDNA. Thus, the 19 kDa protein is hCAP-18, stored as a 'pro-peptide' in specific granules.

Anti-microbial activity of human CAP18 peptides

BACKGROUND

CAP18 derived from rabbit leukocytes is a 142-amino acid protein recently demonstrated to have Lipopolysaccharide (LPS) binding and anti-microbial activity. The C-terminal 37 amino acids of rabbit CAP18 (CAP18(106-142) comprise the LPS-binding and anti-microbial domain. The homologous domain of human CAP18 (huCAP18(104-140) was identified from the recently cloned human CAP18 cDNA.

OBJECTIVES

To evaluate the antimicrobial activity of C-terminal peptides derived from human CAP18.

STUDY DESIGN

Prepare synthetic human CAP18(104-140) and study anti-microbial activity versus various gram-negative and gram-positive bacteria.

RESULTS

Synthetic human CAP18(104-140) has broad anti-microbial activity versus both gram-positive (IC50 = 2.5 micrograms/ml) and gram-negative bacteria (IC50 = 0.5-5 micrograms/ml). Susceptible strains include Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa and Salmonella typhimurium. A 32-amino acid peptide lacking five amino acids from the C-terminus of CAP18(104-140) has higher activity. Unlike previously characterized anti-microbial peptides derived from granulocyte proteins, CAP18(104-140) is active in serum.

CONCLUSIONS

Human CAP18(104-140) or a derivative peptide may have therapeutic potential for bacterial sepsis.

Human CAP18: a novel antimicrobial lipopolysaccharide-binding protein

CAP18 (18-kDa cationic antimicrobial protein) is a protein originally identified and purified from rabbit leukocytes on the basis of its capacity to bind and inhibit various activities of lipopolysaccharide (LPS). Here we report the cloning of human CAP18 and characterize the anti-LPS activity of the C-terminal fragment. Oligonucleotide probes designed from the rabbit CAP18 cDNA were used to identify human CAP18 from a bone marrow cDNA library. The cDNA encodes a protein composed of a 30-amino-acid signal peptide, a 103-amino-acid N-terminal domain of unknown function, and a C-terminal domain of 37 amino acids homologous to the LPS-binding antimicrobial domain of rabbit CAP18, designated CAP18(104-140). A human CAP18-specific antiserum was generated by using CAP18 expressed as a fusion protein with the maltose-binding protein. Western blots (immunoblots) with this antiserum showed specific expression of human CAP18 in granulocytes. Synthetic human CAP18(104-140) and a more active truncated fragment, CAP18(104-135), were shown to (i) bind to erythrocytes coated with diverse strains of LPS, (ii) inhibit LPS-induced release of nitric oxide from macrophages, (iii) inhibit LPS-induced generation of tissue factor, and (iv) protect mice from LPS lethality. CAP18(104-140) may have therapeutic utility for conditions associated with elevated concentrations of LPS.

Prophenin-1, an exceptionally proline-rich antimicrobial peptide from porcine leukocytes

We purified and characterized an unusual antimicrobial peptide, prophenin-1 (PF-1), from porcine leukocytes. The peptide had a mass of 8,683 and contained 79 residues, including 42 (53.2%) prolines and 15 (19.0%) phenylalanines. Its N-terminal 60 residues consisted of three perfect and three nearly perfect repeats of a decamer, FPPPNFPGPR. Prophenin-1 was encoded on a cathelin-containing precursor and showed substantially more activity against E. coli, a Gram-negative bacterium, than against Listeria monocytogenes, a Gram-positive organism, in vitro.

PMAP-37, a novel antibacterial peptide from pig myeloid cells. cDNA cloning, chemical synthesis and activity

A molecular biological approach, based on preproregion homology in the precursors of several diverse antibacterial peptides, was used to clone a pig bone marrow cDNA encoding a novel 167-residue polypeptide. The preproregion of this polypeptide is highly similar to corresponding regions in congeners from pig, cattle and rabbit. It is followed by a unique, cationic, 37-residue sequence, which was predicted to have a high propensity for an alpha-helical conformation. A peptide, termed PMAP-37, corresponding to this sequence, was chemically synthesized and shown to undergo a transition from a random coil to an ordered, mainly helical, conformation on addition of trifluoroethanol. This behaviour is typical of an amphipathic alpha helix, a structure common to several membrane-active, antimicrobial peptides. In vitro experiments showed that PMAP-37 strongly inhibits the growth of several strains of Gram-negative and Gram-positive bacteria, with minimal inhibitory concentrations ranging over 1-4 microM, and permeabilizes the inner membrane of Escherichia coli. Interestingly, the 15-32 stretch of PMAP-37 show a remarkable similarity to N-terminal stretches in cecropins B and A from Drosophila melanogaster and Cecropia hyalophora, respectively. This affords an uncommon example of sequence convergence.

Molecular cloning of Bac7, a proline- and arginine-rich antimicrobial peptide from bovine neutrophils

Bac7 is a 7 kDa proline- and arginine-rich antimicrobial peptide which was purified from bovine neutrophils. We have used PCR to clone the cDNA of Bac7 precursor, a polypeptide of 21,569 Da. This cDNA is highly conserved in the 5' region, with respect to the corresponding region in the precursors of several other structurally unrelated myeloid antimicrobial peptides. Furthermore, a 148 nt non-coding region at the 3' end is 75% homologous to a corresponding region of the cDNA of the precursor of PR-39, a porcine antibacterial peptide which is also proline- and arginine-rich.

Identification of a new member of the protegrin family by cDNA cloning

The porcine leukocyte protegrins are a family of cysteine-rich antimicrobial peptides the primary structures of which combine features of defensins and tachyplesins. We cloned three protegrins from porcine bone marrow mRNA by PCR, including one (PG-4) that was previously unknown. The 691 bp protegrin cDNAs were > 98.8% identical, and each was surrounded by highly conserved 5' and (in some instances) 3' sequences present in structurally dissimilar antimicrobial and LPS-binding peptides of animal leukocytes.

Pig leukocyte cysteine proteinase inhibitor (PLCPI), a new member of the stefin family

A new stefin type low-M(r) cysteine proteinase inhibitor (PLCPI) was isolated from pig polymorphonuclear leukocytes as a contaminant of the cathelin sample. The inhibitor consists of 103 amino acids, and its M(r) was calculated to be 11,768. The inhibitor exhibits considerable sequence identity with inhibitors from the stefin family, particularly with human stefin A. The PLCPI is a fast acting inhibitor of papain and cathepsins L and S (k(ass) > or = 1 x 10(6) M-1 x s-1) and forms very tight complexes with these enzymes (Ki < or = 190 pM). The affinity for cathepsins B and H (Ki > or = 125 nM) was lower. These results also show that the inhibitory activity previously ascribed to cathelin was due to the presence of PLCPI.