Individual and synergistic effects of rabbit granulocyte proteins on Escherichia coli

Affinity purification of crude acid extracts of rabbit polymorphonuclear leukocytes using Escherichia coli (J5) as adsorbent yields the bactericidal/permeability-increasing protein (BPI), two 15-kD species (p15s), and the two most potent (cationic) defensin species (neutrophil peptides [NP] -1 and -2). Tested in buffered isotonic medium, the relative antibacterial potency of these proteins against E. coli J5 is BPI (IC50 0.2 nM) > p15A (10 nM) > NP -1 (400 nM). Sublethal doses of p15A or NP-1 can synergize with BPI to decrease the dose required to inhibit the growth of E. coli by up to 50-fold. BPI and p15A display similar features of antibacterial action distinct from defensin NP-1, but NP-1 acts synergistically only with BPI and not with p15A. All aspects of the combined action of BPI and NP-1 resemble those observed with higher concentrations of BPI alone, implying that NP-1 enhances BPI potency. Neither NP-1 nor p15A alter the amount of BPI binding to E. coli but BPI enhances binding of p15A to E. coli, raising the possibility that synergy between these two proteins may occur at least partially at the level of binding. The potent synergistic actions of these proteins can also be demonstrated against serum-resistant clinical isolates of encapsulated E. coli tested in whole blood and plasma ex vivo, suggesting that such combined action may contribute to host defense in vivo.

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.

Inhibition of intracellular Histoplasma capsulatum replication by murine macrophages that produce human defensin

Although purified defensins are effective microbicides in vitro, their operation within intact phagocytes has not been established. To address this question, we inserted cDNA encoding human defensin HNP-1 into a pBabe/neo retroviral vector and transduced it into RAW 264.7 cells, a murine macrophage line that lacks endogenous defensins. We isolated five independent clones of HNP-1-transduced cells, all of which secreted prodefensin and contained small amounts of fully processed HNP-1. The two clones that produced the largest amounts of defensin (clones 5 and 14), together with wild-type RAW cells and pBabe/neo-transduced RAW cells (control), were used for the present study. All cells were grown in Dulbecco's modified Eagle's medium-F12 medium that contained 10% heat-inactivated fetal bovine serum and gentamicin. The medium used for the transduced cells contained aminoglycoside G418 in lieu of gentamicin. Both wild-type and transduced cells were placed in antibiotic-free medium 96 h prior to challenge with a yeast-phase strain of Histoplasma capsulatum. Phagocytosis of yeast cells was allowed to proceed for 90 min and was followed by washing and further incubation for 18.5 h. Whereas the phagocytic index did not differ significantly among the four cell populations under study, the mean level of intracellular growth of H. capsulatum in the defensin-transduced RAW cells was significantly lower than those observed for any other cell types (P < 0.05). These findings constitute the first instance of xenogeneic expression of an antimicrobial peptide by phagocytes and suggest that macrophages can be armed with defensins to enhance their ability to restrict certain intracellular pathogens.

Gallinacins: cysteine-rich antimicrobial peptides of chicken leukocytes

We purified three homologous antimicrobial peptides ('gallinacins') from chicken leukocytes, examined their antimicrobial activity in vitro, and established their primary sequences by a combination of gas phase microsequencing and on-line LC-ESI-MS analysis of endo- and exoprotease peptide digests. The peptides contained 36-39 amino acid residues, were relatively cationic due to their numerous lysine and arginine residues, and each contained 3 intramolecular cystine disulfide bonds. Gallinacins showed primary sequence homology to the recently delineated beta-defensin family, heretofore found only in the respiratory epithelial cells and neutrophils of cattle, suggesting that beta-defensins originated at least 250 million years ago, before avian and mammalian lineages diverged. The 9 invariant residues (6 cysteines, 2 glycines and 1 proline) common to avian gallinacins and bovine beta-defensins are likely to constitute the essential primary structural motif of this ancient family of host-defense peptides.

Defensins: a family of antimicrobial and cytotoxic peptides

Defensins are antimicrobial and cytotoxic peptides that contain 29-35 amino acid residues, including 6 invariant cysteines that form 3 intramolecular disulfide bonds. They constitute more than 5% of the total cellular protein of human and rabbit neutrophils (PMN), and are also produced by rabbit lung macrophages and by murine and human small intestinal Paneth cells. Defensins exerted antimicrobial effects in vitro against many Gram-positive and Gram-negative bacteria, fungi, mycobacteria and some enveloped viruses, and were cytotoxic to a wide range of normal and malignant targets, including cells resistant to TNF-alpha and NK-cytolytic factor. Human and rabbit defensins formed voltage-sensitive channels in a variety of planar lipid bilayers when a negative voltage of approximately 70-90 mV was applied to the contralateral side. These channels showed modest anion selectivity and their formation was strongly influenced by defensin concentration. Although most other channel-forming peptides have prominent alpha-helical domains, the structure of defensin molecules is primarily composed of antiparallel beta-sheets. Studies with various prokaryotic and eukaryotic cells provided convincing evidence that defensins killed these targets by forming voltage-regulated channels in the susceptible cell's membrane. The broad spectrum of defensin-susceptible targets and the abundance of defensins in specialized host defense cells of the blood, lungs and intestinal tract suggest that defensins could play a significant role in innate immunity to infection and neoplasia.

In vitro candidastatic properties of the human neutrophil calprotectin complex

Microbiostatic mechanisms may contribute substantially to host defense against infection by certain microbes. We studied the candidastatic activity of human neutrophils, neutrophil cytosol, and neutrophil-derived "calprotectin," a cytosolic protein complex comprised of two subunits, MRP8 and MRP14. Intact neutrophils, neutrophil lysates (prepared by ultrasonic disruption, freezing and thawing, or nonionic detergent extraction), and granule-depleted neutrophil cytosol were effective in restricting the growth of Candida albicans in a nutrient-rich tissue culture medium, RPMI 1640. Neither a subcellular fraction enriched in neutrophil granules nor selected purified granule components (lactoferrin, myeloperoxidase, cathepsin G, leukocyte elastase, lysozyme, and defensins) exerted candidastatic activity in this medium. Gel filtration liquid chromatography, anion exchange FPLC, and SDS-PAGE showed that the fungistatic factor in neutrophil cytosol was associated with the calprotectin complex. Its antifungal effects included restriction of yeast phase and mycelial growth and inhibition of glucose incorporation by yeast phase cultures. The antifungal effects of calprotectin were sustained for over 120 h and were inhibited by zinc. However, studies with 65Zn-enriched RPMI suggested that the candidastatic effects of calprotectin were not mediated by sequestration or binding of zinc. After reversed phase HPLC, calprotectin fractions containing MRP14 exhibited fungistatic activity, whereas fractions depleted of MRP14 but enriched for MRP8 lacked fungistatic activity. The results support a potentially significant role for the calprotectin complex of neutrophil cytosol in antifungal defense and suggest that MRP14 is of key importance in that activity.

In vitro candidastatic properties of the human neutrophil calprotectin complex

Microbiostatic mechanisms may contribute substantially to host defense against infection by certain microbes. We studied the candidastatic activity of human neutrophils, neutrophil cytosol, and neutrophil-derived "calprotectin," a cytosolic protein complex comprised of two subunits, MRP8 and MRP14. Intact neutrophils, neutrophil lysates (prepared by ultrasonic disruption, freezing and thawing, or nonionic detergent extraction), and granule-depleted neutrophil cytosol were effective in restricting the growth of Candida albicans in a nutrient-rich tissue culture medium, RPMI 1640. Neither a subcellular fraction enriched in neutrophil granules nor selected purified granule components (lactoferrin, myeloperoxidase, cathepsin G, leukocyte elastase, lysozyme, and defensins) exerted candidastatic activity in this medium. Gel filtration liquid chromatography, anion exchange FPLC, and SDS-PAGE showed that the fungistatic factor in neutrophil cytosol was associated with the calprotectin complex. Its antifungal effects included restriction of yeast phase and mycelial growth and inhibition of glucose incorporation by yeast phase cultures. The antifungal effects of calprotectin were sustained for over 120 h and were inhibited by zinc. However, studies with 65Zn-enriched RPMI suggested that the candidastatic effects of calprotectin were not mediated by sequestration or binding of zinc. After reversed phase HPLC, calprotectin fractions containing MRP14 exhibited fungistatic activity, whereas fractions depleted of MRP14 but enriched for MRP8 lacked fungistatic activity. The results support a potentially significant role for the calprotectin complex of neutrophil cytosol in antifungal defense and suggest that MRP14 is of key importance in that activity.

Protegrins: leukocyte antimicrobial peptides that combine features of corticostatic defensins and tachyplesins

Porcine leukocytes contained three homologous peptides, PG-1, 2 and 3, that manifested potent microbicidal activity against Escherichia coli, Listeria monocytogenes and Candida albicans in vitro. The peptides ('protegrins') were composed of 16 (PG-2) or 18 amino acid residues, and, like tachyplesins (broad-spectrum antibiotic peptides of horseshoe crab hemocytes), they contained two intramolecular cystine disulfide bonds. Considerably smaller than defensins, protegrins nevertheless showed substantial homology to them, especially to the 'corticostatic' rabbit defensin, NP-3a. The relatively simple structure of protegrins should provide useful prototypes for constructing congeners with selectively enhanced host defense activities.

Selective inhibition of microbial serine proteases by eNAP-2, an antimicrobial peptide from equine neutrophils

Equine neutrophil antimicrobial peptide 2 (eNAP-2), a recently described antimicrobial peptide isolated from equine neutrophils, was found to selectively inactivate microbial serine proteases (subtilisin A and proteinase K) without inhibiting mammalian serine proteases (human neutrophil elastase, human cathepsin G, and bovine pancreatic trypsin). Although the primary structure of eNAP-2 resembled that of several known antiproteases that belong to the 4-disulfide core peptide family, this pattern of selectivity is unique. eNAP-2 formed a noncovalent complex with native subtilisin A or proteinase K but did not associate with these enzymes if they had been treated with phenylmethylsulfonyl fluoride, a serine protease inhibitor. The eNAP-2-microbial protease complex was disrupted by boiling or by exposure to low pH. We suggest that eNAP-2 exerted selective antiproteinase activity by binding tightly but noncovalently to the active site of subtilisin A or proteinase K. Since microbial exoproteases may act as virulence factors, the combined antimicrobial and antiprotease activities of eNAP-2 could allow it to play an important role in neutrophil-mediated antimicrobial defenses.

Antimicrobial proteins of murine macrophages

Three murine microbicidal proteins (MUMPs) were purified from cells of the murine macrophage cell line RAW264.7 that had been activated by gamma interferon. Similar proteins were also present in nonactivated RAW264.7 cells, in cells of the murine macrophage cell line J774A.1, and in resident and activated murine peritoneal macrophages. MUMP-1, MUMP-2, and MUMP-3 killed Salmonella typhimurium, Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, Mycobacterium fortuitum, and Cryptococcus neoformans in vitro. MUMP-1 resembled an H1 histone but was unusual because its N-terminal residue (serine) was not N acetylated. Although MUMP-2 was N terminally blocked, its high lysine/arginine ratio and its reactivity with an antibody to H1 histones suggested that it also belonged to the H1 histone family. MUMP-3 was identical to histone H2B in 30 of 30 amino-terminal residues. Although the antimicrobial properties of histones have been recognized for decades, this is the first evidence that such proteins may endow the lysosomal apparatus of macrophages with nonoxidative antimicrobial potential. Other MUMPs, including some with a more restricted antimicrobial spectrum and one that appeared to be induced in RAW264.7 cells after gamma interferon stimulation, were noted but remain to be characterized.

[Rat bladder ubiquitin-like molecule: isolation, purification and N-terminal sequencing]

A Ubiquitin-like peptide was accidentally isolated from rat bladder by using 5% acetic acid wash while we were isolating antibacterial peptides. The purified molecule was obtained by reverse phase high performance liquid chromatography. Gas phase microsequence analysis indicated the N-terminal sequences of the molecule as follows: MET-GLN-ILE-PHE-VAL-LYS-THR-LEU-THR-GLY-LYS-THR-ILE-THR-LEU- GLU-VAL-GLU-PRO-SER-ASP-THR-ILE-GLU-ASN, which is homologous to human ubiquitin. Ubiquitin plays a role in the differentiation of pre-B lymphocytes, Thus, it is suggested from the findings of this molecule and the endogenous antibacterial polypeptides in mucosa or mucosal epithelium that mucosal epithelium also might be one of immune cells or immunity-associated cells, which may secrete effector molecules directly to kill adherent microbes and produce regulating factors in mucosal immune response.

Defensins: antimicrobial and cytotoxic peptides of mammalian cells

Defensins are antimicrobial and cytotoxic peptides that contain 29-35 amino acid residues, including six invariant cysteines whose intramolecular disulfide bonds cyclize and stabilize them in a complexly folded, triple-stranded beta-sheet configuration. Generated by the proteolytic processing of 93-95 amino acid precursor peptides, the constitute > 5% of the total cellular protein in human and rabbit neutrophils (polymorphonucleated neutrophils--PMN) and are also produced by rabbit lung macrophages and by mouse and rabbit small intestinal Paneth cells. Despite their prominence in rat PMN, defensins are not found in murine PMN. The antimicrobial spectrum of defensins includes gram positive and gram negative bacteria, mycobacteria, T. pallidum, many fungi, and some enveloped viruses. Defensins exert nonspecific cytotoxic activity against a wide range of normal and malignant targets, including cells resistant to TNF-alpha and NK-cytolytic factor. They appear to kill mammalian target cells and microorganisms by a common mechanism, which involves initial electrostatic interactions with negatively charged target cell surface molecules (likely the head groups of polar membrane lipids), followed by insertion into the cell membranes which they permeabilize, forming voltage-regulated channels. In addition to their antimicrobial and cytotoxic properties, some defensins act as opsonins, while others inhibit protein kinase C, bind specifically to the ACTH receptor and block steroidogenesis or act as selective chemoattractants for monocytes. Defensins are a newly delineated family of effector molecules whose contribution to host defense, inflammation, and cytotoxicity may be considerable for humans, even though it is unlikely to be revealed by experimentation with mice.

In vitro antimicrobial activity of the human neutrophil cytosolic S-100 protein complex, calprotectin, against Capnocytophaga sputigena

Calprotectin is a complex of two anionic proteins found in abundance in the cytosol of neutrophils, certain macrophages, and oral epithelial keratinocytes. Bacteria of the genus Capnocytophaga are pathogens of periodontal origin which can cause systemic infection in neutropenic subjects. Recently, it has been observed that Capnocytophaga may be internalized by neutrophils within the cytosol rather than within a membrane-delimited phagosome. The purpose of this study was to test the in vitro antibacterial effect of the cytosolic complex, calprotectin, against Capnocytophaga sputigena. Calprotectin was purified from the cytosol of human neutrophils by gel filtration and anion exchange FPLC, and it exerted potent in vitro antimicrobial effects against C. sputigena. Net bacteriostatic activity was exerted up to 18 h, after which bactericidal effects were observed. Both net bacteriostatic and bactericidal activity occurred at concentrations above 20 micrograms/mL and exhibited identical dose-response characteristics. Particle counts increased in the presence of calprotectin, despite net bacteriostasis as assessed by changes in colony-forming units (CFU). Dose-response characteristics and direct particle counts suggested that net bacteriostatic effects were the result of balanced cell division and death, rather than suspension of cell division. We conclude that calprotectin can be a significant contributor to host defense against infection by Capnocytophaga.

Purification of cysteine-rich bioactive peptides from leukocytes by continuous acid-urea-polyacrylamide gel electrophoresis

A new continuous acid-urea-polyacrylamide gel electrophoresis (CAU-PAGE) preparative method was developed and used to purify rabbit and human defensins. With it, we identified two post-translationally modified forms of rabbit defensins NP-1 and NP-2, and purified a processed RANTES (beta-intercrine) peptide from leukophoresed human leukocytes. CAU-PAGE afforded approximately 70% recovery of rabbit defensin NP-5. The recovered defensins were not N-terminally modified, and their in vitro antimicrobial activity was equivalent to that of defensins purified by previously described chromatographic methods. Since CAU-PAGE is performed under nonreducing conditions, it should be especially useful for purifying cationic peptides with intramolecular disulfide bonds, such as defensins and alpha or beta-intercrines.

eNAP-2, a novel cysteine-rich bactericidal peptide from equine leukocytes

We purified a novel cysteine-rich antibiotic peptide, eNAP-2 (M(r), approximately 6,500), from acid extracts of equine neutrophils by sequential gel filtration and reversed-phase high-performance liquid chromatography and determined its partial N-terminal amino acid sequence. Although its cysteine motif distinguished eNAP-2 from all other currently known endogenous antibiotic peptides, including defensins and granulins, it showed substantial sequence similarity to WDNM1, a putative member of the four-disulfide-core protein family that also includes animal and human antiproteases, snake venom neurotoxins, and rat and mouse whey proteins. The antibacterial properties of eNAP-2 were tested against several equine uterine pathogens, namely, Streptococcus zooepidemicus, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Killing of S. zooepidemicus was very efficient, as evidenced by a 94% decrease in numbers of CFU per milliliter after exposure to 100 micrograms of eNAP-2 per ml (approximately 15 microM) for 2 h. Exposure of E. coli and P. aeruginosa to 200 micrograms of eNAP-2 per ml for 2 h resulted in 90.2 and 77.6% reduction, respectively, in the numbers of CFU per milliliter. Bacteriostasis, without bactericidal activity, occurred after K. pneumoniae was incubated with 200 micrograms of eNAP-2 per ml. Additional studies will be required in other species and cell types to determine whether eNAP-2 is restricted to equine neutrophils or is the index member of a larger family of endogenous antibiotics.

Activity of defensins from human neutrophilic granulocytes against Mycobacterium avium-Mycobacterium intracellulare

We have examined the activity of defensins from human neutrophilic granulocytes against Mycobacterium avium-Mycobacterium intracellulare. M. avium-M. intracellulare at 2.5 x 10(6)/ml or 2.5 x 10(8)/ml was cultured in the presence of defensins at 37 degrees C from 4 to 48 h. After incubation, CFU were enumerated. Human neutrophil peptide 1 (HNP-1) at 5 micrograms/ml had the ability to kill M. avium-M. intracellulare. Treatment with HNP-1 resulted in significant (96.3 to 97.7%) killing of M. avium-M. intracellulare, even after taking clumping into consideration. This activity was not affected by the presence of calcium (0.5 and 1.0 mM), magnesium (0.5 and 1.0 mM), or sodium chloride (25, 50, and 100 mM). The optimal pH for bactericidal activity was higher than 5. We tested numerous M. avium-M. intracellulare strains, and HNP-1 was successful in killing every strain, although the degree of killing varied among them (34.2 to 87.2%). Additionally, this activity was independent of colonial morphology. We also examined the activity of HNP-2 and HNP-3 against M. avium-M. intracellulare and found that they were as effective in killing M. avium-M. intracellulare as HNP-1 was. These observations suggest that defensins may play an important role in the host defense against M. avium-M. intracellulare.

Cryptdins: antimicrobial defensins of the murine small intestine

Paneth cells are specialized small intestine epithelial cells that contain lysozyme, possess phagocytic properties, and secrete cytoplasmic granules into the intestinal crypt lumen after the entry of bacteria. Recent studies by Ouellette and associates (A. J. Ouellette, R. M. Greco, M. James, D. Frederick, J. Naftilan, and J. T. Fallon, J. Cell Biol. 108:1687-1695, 1989) indicated that murine Paneth cells produce prodefensin mRNA, but the properties of its peptide product were not reported. We purified two closely related defensins, cryptdin 1 and cryptdin 2, from a subcellular fraction of murine small intestine cells that was enriched in Paneth cells. Both peptides contained 35 amino acid residues, including the characteristic defensin "signature" of six invariantly conserved cysteines. Cryptdins 1 and 2 were approximately 90 to 95% homologous to each other and to the carboxy-terminal domain of the 93-amino-acid defensin precursor, cryptdin A, described by Ouellette and associates (Ouellette et al., J. Cell Biol. 108:1687-1695, 1989). Both cryptdins exerted bactericidal activity against Listeria monocytogenes EGD and Escherichia coli ML-35p in vitro. Their potency exceeded that of human neutrophil defensin HNP-1 but was considerably lower than that of NP-1, a defensin produced by rabbit neutrophils and alveolar macrophages. Both cryptdins killed mouse-avirulent Salmonella typhimurium 7953S (phoP) much more effectively than its phoP+, mouse-virulent, isogenic counterpart, S. typhimurium 14028S. Our data indicate that mouse intestinal prodefensins are processed into 35-amino-acid mature defensins (cryptdins) with broad-spectrum antimicrobial properties. The production of defensins and lysozyme by Paneth cells may enable them to protect the small intestine from bacterial overgrowth by autochthonous flora and from invasion by potential pathogens that cause infection via the peroral route, such as L. monocytogenes and Salmonella species.

Mouse neutrophils lack defensins

Defensins are broad-spectrum antimicrobial peptides that are abundant in human, rat, and rabbit neutrophils. We now report that neutrophils from nine strains of mice lacked appreciable defensin content. Mice may therefore be imperfect experimental surrogates for humans or rats in models of infection in which neutrophil function is significant.

Identification of eNAP-1, an antimicrobial peptide from equine neutrophils

Endogenous, cysteine-rich antimicrobial peptides known as defensins are prominent components of human, rabbit, and rat neutrophils, yet little is known about their occurrence in other mammalian species. Although we did not detect mature (i.e., processed) defensins in equine neutrophil granules, we found that these granules contained small amounts of other cysteine-rich peptides with antimicrobial activity. One of these, eNAP-1, was purified by a combination of gel permeation and reversed-phase high-performance liquid chromatography from acid extracts prepared from the cytoplasmic granules of equine neutrophils. The molecular mass of eNAP-1 was approximately 7.2 kDa, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Amino acid analysis revealed that eNAP-1 had an unusually high cysteine content and that it was relatively enriched in alanine, glycine, lysine, and proline residues. The partial (N-terminal) amino acid sequence of eNAP-1 was DVQCGEGHFCHDXQTCCRASQGGXACCPYSQGVCCADQRHCCPVGF. Thirty-six of these residues (78.3%) were identical to those of a recently cloned human neutrophil peptide of unknown function and belonging to the granulin family. Homologous peptides have also been noted in rat bone marrow cells and rat kidney epithelins. We tested the ability of eNAP-1 to kill several equine uterine pathogens. Streptococcus zooepidemicus was killed most effectively, sustaining a greater than 99.8% decrease in CFU per milliliter after a 2-h exposure to 100 micrograms of eNAP-1 per ml (approximately 15 microM). Escherichia coli and Pseudomonas aeruginosa were somewhat less susceptible, manifesting 87.0 and 87.1% mean decreases in CFU per milliliter, respectively, after incubation for 2 h with 200 micrograms of eNAP-1 per ml. Klebsiella pneumoniae numbers were not significantly reduced after exposure to eNAP-1. These antimicrobial properties suggest that eNAP-1 may contribute to phagocyte-mediated host defense against equine infections.

Characterization of defensin precursors in mature human neutrophils

Human defensins HNP-1 and -3 are broad spectrum antimicrobial peptides that are synthesized by human neutrophils as 94 amino acid (aa) precursors that require proteolytic removal of 64 amino-terminal residues to produce the mature defensins. Recent studies have shown that the early proteolytic processing events include two sequential cleavages, each removing 19 amino-terminal aa residues, that yield 75 aa and 56 aa prodefensins, respectively. The subsequent processing steps that convert these 56 aa prodefensins to mature (30 aa) HNP-1 and HNP-3 are not yet known. We identified four new defensin precursors in mature normal neutrophils. The most abundant of these were two 39 aa forms that resulted from the monobasic endoproteolytic cleavage of proHNP-1 and proHNP-3. The presence of two proline residues in the vicinity of this newly defined scission site suggested that this cleavage might be "proline-directed." Smaller amounts of the 34 aa and 32 aa prodefensin forms were also found. It remains to be established if these 39, 34, and 32 aa prodefensins are obligate intermediates in the prodefensin processing pathway, or arise from side reactions. In either event, because these prodefensin intermediates accounted for only 0.25% of the total defensin content, proteolytic conversion of 56 aa prodefensins to mature defensins appears to be a highly efficient process.