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PubMed1990

Analysis of side-chain conformational distributions in neutrophil peptide-5 NMR structures.

The side-chain conformations have been analyzed in the antimicrobial peptide, Neutrophil Peptide-5 (NP-5), whose structure was independently generated from nmr-derived distance constraints using a distance geometry algorithm. The side-chain and peptide dihedral angle distributions in the nmr structures were compared with those constructed from a data base of high-resolution protein crystal structures. The side-chain conformational preferences for NP-5 in solution are significantly different from those observed in the crystal structure data base. These results indicate that the side-chain conformations are quite disordered for many of the residues of NP-5. The absence of a correlation between the width of the conformational distribution and surface accessibility suggests that the disorder may be due to limitations in the structural information extracted from the nmr data rather than to molecular motion. However, it is also observed that the degree of conformational disorder is only weakly correlated with the number of nuclear Overhauser enhancements to a given side chain. Possible reasons for this are discussed. Molecular mechanics refinement of these structures did not significantly change the side-chain populations. Anomolously wide distributions are observed for rotations about the peptide bonds and the disulfide bonds in the NP-5 distance geometry structures, which are improved by the refinement. The very high degree of order observed for the central dihedral angle of the disulfide bond in the high-resolution crystal data base suggests that the rotation about this bond in proteins is determined by the local potential.

Algorithms↗

PubMed1992

Cationic defensins arise from charge-neutralized propeptides: a mechanism for avoiding leukocyte autocytotoxicity?

Defensins, small cationic polypeptides with antimicrobial and cytotoxic properties, are among the principal constituents of cytoplasmic granules of mammalian neutrophils and certain macrophages. To identify conserved structural features of defensin precursors that may be important for their targeting to cytoplasmic granules or for prevention of autocytotoxicity, we isolated and sequenced three neutrophil-specific rabbit defensin cDNAs that code for preproprotein precursors to the mature defensins NP-3a, NP-4, and NP-5. The preprodefensins NP-3a, NP-4, and NP-5, like the previously characterized preprodefensins, lack consensus sequences for N-linked glycosylation, suggesting that defensins are targeted to lysosome-like granules by a mechanism not dependent on the mannose-6-phosphate receptor. Analysis of all seven known myeloid prodefensins revealed a structure wherein an anionic propiece neutralizes the cationicity of the mature peptide. Because defensins apparently require cationic epitopes for cell membrane permeabilization and cytotoxicity, charge neutralization of mature peptides by their anionic propieces may prevent autocytotoxicity during defensin synthesis and processing.

Amino Acid Sequence↗

PubMed1991

The effect of HP-1 and related neutrophil granule peptides on DNA synthesis in HL60 cells.

The recently isolated cysteine- and arginine-rich peptides of the neutrophil primary granule and the murine intestinal Paneth cell, named defensins or corticostatins, have a number of distinct biological properties. We report the effects of three of these peptides HP-1, HP-1-56 and HP-4 on the incorporation of [3H]thymidine into the DNA of the leukemic cell line HL60. HP-1 and HP-1-56, but not HP-4, inhibited DNA synthesis at 1-50 nM without causing cell death. At higher concentrations the effect was reversed, resulting in a small, but statistically significant increase in DNA synthesis at 1 microM. In contrast HP-4 had no effect on HL60 cells at nanomolar concentrations but was strongly cytotoxic at micromolar concentrations.

Amino Acid Sequence↗

PubMedDate not supplied

The levels and biologic action of the human neutrophil granule peptide HP-1 in lung tumors.

HP-1 is the most abundant human representative of a recently discovered class of neutrophil cystine- and arginine-rich peptides. These peptides have many potentially regulatory activities expressed at nanomolar concentrations. To establish the levels of HP-1 that can accumulate in human lung tumors and nondiseased lung fragments, tissues were extracted for their peptide content. The extracts were purified on reverse phase HPLC, and HP-1 and related peptides were identified by sequence analysis and their concentrations in the tissue quantitated by amino acid analysis. Immunohistochemistry was performed and strongly suggests that HP-1 is confined to granulocytes under most circumstances, and indicates that the levels of HP-1 measured in the tumors reflect the levels obtained when solid tissue is infiltrated by neutrophils. The maximum observed levels were 26 nanomoles per gram wet weight of tissue. Attempts were then made to correlate this level to the cytotoxic potential of HP-1 by performing in vitro cytotoxicity dose-response curves on several cell lines. Most cells were killed at between 1 and 8 microM, and the response depended on the growth conditions of the cells. The levels of HP-1 that accumulate in tumors can exceed the in vitro cytolytic concentrations. The levels are also considerably in excess of those required to exert in vitro regulatory actions.

Amino Acid Sequence↗

PubMed2026

Exploring precision risk in pediatric vesicoureteral reflux: Innate immune gene variations and reflux outcomes in the RIVUR cohort.

INTRODUCTION: Children with vesicoureteral reflux (VUR) are at increased risk for morbidity from recurrent urinary tract infections (UTIs), yet the factors influencing spontaneous VUR resolution remain poorly defined. This study evaluates whether genetic variations in key urinary innate immune effectors (DEFA1A3, DMBT1, and RNASE7) influences VUR resolution and interacts with prophylaxis to alter clinical response. METHODS: We conducted a secondary analysis of 303 RIVUR participants with available DEFA1A3 and DMBT1 copy number variation (CNV) data and RNASE7 rs1263872 genotype. Primary outcomes were (1) VUR improvement (decrease in grade) and (2) VUR resolution at study exit. Multivariable logistic regression models included genotype, treatment, and their interactions, adjusting for age, sex, baseline grade (high vs low), laterality, bowel/bladder dysfunction, and any UTI. Internal validation used 2000-sample bootstrap with bias-corrected and accelerated confidence intervals and influence diagnostics. RESULTS: Clinical covariates did not significantly predict VUR improvement. Children with DEFA1A3 CNV >5 had higher odds of improvement (OR 2.36, 95% CI 1.12-4.96, p = 0.023), an effect that remained significant in bootstrap analyses. High-grade VUR was associated with lower odds of resolution (OR 0.34, 95% CI 0.12-0.94, p = 0.038). A significant interaction was observed between prophylaxis and high DMBT1 copy number for VUR resolution (interaction OR 2.99, 95% CI 1.11-8.04, p = 0.031); no interaction was seen for improvement. RNASE7 rs1263872 was not associated with either outcome. CONCLUSION: Innate immune gene variation may contribute to heterogeneity in VUR outcomes. High DEFA1A3 copy number was associated with reflux improvement and a DMBT1-prophylaxis interaction was associated with reflux resolution. The results of this study is hypothesis-generating and prompt further evaluation to assess whether a subset of children may experience structural benefit from prophylaxis or have a more favorable natural history based on their innate immune genotype.

Humans↗

PubMed1992

NMR studies of defensin antimicrobial peptides. 1. Resonance assignment and secondary structure determination of rabbit NP-2 and human HNP-1.

Two-dimensional nuclear magnetic resonance spectroscopy has been used to make resonance assignments of the proton spectra of two defensin antimicrobial peptides, human neutrophil peptide HNP-1 and rabbit neutrophil peptide NP-2. The secondary structures of these peptides were determined from analysis of the proton-proton NOEs and from the positions of slowly exchanging amide protons. Both peptides contain a long stretch of a double-stranded antiparallel beta-sheet in a hairpin conformation that contains a beta-bulge, a short region of triple-stranded beta-sheet, and several tight turns. The NMR results clearly show that HNP-1 forms a dimer or higher order aggregate in solution and that Pro8 exists as a cis peptide bond. The NMR data on these peptides are compared with NMR data for a homologous peptide NP-5 [Bach, A. C., Selsted, M. E., & Pardi, A. (1987) Biochemistry 26, 4389-4397]. Analysis of the conformation-dependent proton chemical shifts shows that it is not possible to confidently judge the structural similarity of the three defensins from chemical shift data alone. However, comparison of the 3JHN alpha coupling constants in NP-2 and NP-5 indicates that the backbone conformations for these peptides are very similar. A more detailed comparison of the solution conformations of the defensins peptides is made in the following paper in this issue where the NMR data are used as input for distance geometry and molecular dynamics calculations to determine the three-dimensional structures of HNP-1 and NP-2.

Amino Acid Sequence↗

PubMed1992

NMR studies of defensin antimicrobial peptides. 2. Three-dimensional structures of rabbit NP-2 and human HNP-1.

The solution structure of two homologous naturally occurring antimicrobial peptides, rabbit defensin NP-2 and human defensin HNP-1, have been determined by two-dimensional nuclear magnetic resonance spectroscopy, distance geometry, and restrained molecular dynamics calculations. The structure of these defensins consists of an antiparallel beta-sheet in a hairpin conformation, a short region of triple-stranded beta-sheet, several tight turns, and a loop region that has a well-defined local structure but with a global orientation that is not well-defined with respect to the rest of the molecule. The solution structures of these two peptides are compared with the solution and crystal structures of two other homologous defensins. The structures for the defensins are also compared with known structures of other naturally occurring antimicrobial peptides.

Animals↗

PubMed1989

Solution structures of proteins from NMR data and modeling: alternative folds for neutrophil peptide 5.

The structure of neutrophil peptide 5 in solution has recently been reported (Pardi et al., 1988). The structure determination was accomplished by using a distance geometry algorithm and 107 interproton distance constraints obtained from 2D NMR data. In each of the eight independent solutions to the distance geometry equations, the overall fold of the polypeptide backbone was identical and the root mean square (rms) deviation between backbone atoms of the superimposed structures was small (approximately 2.4 A). In this paper we report additional NP-5 structures obtained by using a new structure generation algorithm: a Monte Carlo search in torsion angle space. These structures have a large rms backbone deviation from the distance geometry structures (approximately 5.0 A). The backbone topologies differ in significant respects from the distance geometry structures and from each other. Structures are found that are pseudo mirror images of part or all of the fold corresponding to that first obtained with the distance geometry procedure. For small proteins, the problem of distinguishing the correct structure among pseudo mirror images is likely to be greater than previously recognized. When a set of test distance constraints constructed from a novel Monte Carlo structure is used as input in the distance geometry algorithm, the fold of the resulting structure does not correspond to that of the target. The results also demonstrate that the previously accepted criteria (the magnitude of the rms deviation between multiple solutions of the distance geometry equations) for defining the accuracy and precision of a peptide structure generated from NMR data are inadequate. An energetic analysis of structures corresponding to the different folding topologies has been carried out. The molecular mechanics energies obtained by minimization and molecular dynamics refinement provide sufficient information to eliminate certain alternative structures. On the basis of a careful comparison of the different trial structures with the experimental data, it is concluded that the NP-5 peptide fold which was originally reported is most consistent with the data. An alternative fold corresponding to structures with low energies and small total distance violations is ruled out because for this fold predicted NOEs are not observed experimentally.

Blood Proteins↗

PubMed1990

Defensins.

Defensins are a family of small, variably cationic proteins which are highly abundant in the granules of mammalian phagocytes. Three defensins, HNP-1, 2, and 3, comprise 30-50% of total protein in azurophil granules of human neutrophils. Some defensins are broadly antimicrobial, antiviral and cytotoxic, while others are chemotactic, opsonic, or may modulate hormonal responses. The defensin molecule typically consists of 29-34 amino acids with a conserved pattern of disulfide linkage among its 6 cysteines. The three-dimensional fold of defensins forms a highly amphiphilic molecule. Microbicidal and cytotoxic properties of defensins are most likely a consequence of their ability to insert into biological membranes and to generate pores. Defensins are synthesized by phagocytes or their precursors as a 94-95 amino acid charge-neutralized preprodefensin, an arrangement which may avoid cytotoxic injury to the phagocyte. Although defensins were recognized only recently, the existence of homologs in certain invertebrates suggests that they are ancestral components of the host defense system.

Amino Acid Sequence↗

PubMed1991

Crystal structure of defensin HNP-3, an amphiphilic dimer: mechanisms of membrane permeabilization.

Defensins (molecular weight 3500 to 4000) act in the mammalian immune response by permeabilizing the plasma membranes of a broad spectrum of target organisms, including bacteria, fungi, and enveloped viruses. The high-resolution crystal structure of defensin HNP-3 (1.9 angstrom resolution, R factor 0.19) reveals a dimeric beta sheet that has an architecture very different from other lytic peptides. The dimeric assembly suggests mechanisms by which defensins might bind to and permeabilize the lipid bilayer.

Amino Acid Sequence↗

PubMed1990

Characterization of defensin resistance phenotypes associated with mutations in the phoP virulence regulon of Salmonella typhimurium.

The defensin sensitivities of Salmonella typhimurium strains with mutations in the phoP/phoQ two-component virulence regulon were tested by using purified defensins NP-1 and NP-2. Strains with mutations in either gene of the regulatory pair (phoP [transcriptional activator] or phoQ [membrane sensor kinase]) had increased sensitivities to defensin. The predicted periplasmic domain of the PhoQ protein contained a markedly anionic domain that could interact with cationic proteins and that could be responsible for resistance to defensin. Because insertion mutations in phoP are polar on phoQ, we constructed strains that expressed the PhoQ protein in the absence of PhoP to test whether resistance to defensin requires only the phoQ gene product. We found that resistance to defensin requires the function of both components of this regulatory system, because strains expressing PhoQ without PhoP were still markedly sensitive to defensins. This implied that a pag (phoP-activated gene) product is responsible for defensin resistance. We also tested for the ability of defensins NP-1, NP-5, and HNP-1 to activate pag expression and found that these peptides have no effect. Defensin resistance is not the only virulence characteristic controlled by the PhoP-PhoQ regulon because mutations in pagC, as well as ones in the phoP locus that resulted in constitutive pag activation (phenotype PhoPc), had no effect on defensin resistance, even though they rendered the organism avirulent and deficient in survival within macrophages. The virulence defect conferred by mutations in the phoP-phoQ two-component regulatory system is not completely explained by alterations in resistance to cationic proteins and involves the control of other proteins necessary for S. typhimurium survival within macrophages.

Animals↗

PubMed1990

In vitro sensitivity of oral, gram-negative, facultative bacteria to the bactericidal activity of human neutrophil defensins.

Neutrophils play a major role in defending the periodontium against infection by oral, gram-negative, facultative bacteria, such as Actinobacillus actinomycetemcomitans, Eikenella corrodens, and Capnocytophaga spp. We examined the sensitivity of these bacteria to a mixture of low-molecular-weight peptides and highly purified individual defensin peptides (HNP-1, HNP-2, and HNP-3) isolated from human neutrophils. Whereas the Capnocytophaga spp. strains were killed significantly by the mixed human neutrophil peptides, the A. actinomycetemcomitans and E. corrodens strains were resistant. Killing was attributable to the defensins. The bactericidal activities of purified defensins HNP-1 and HNP-2 were equal, and both of these activities were greater than HNP-3 activity against strains of Capnocytophaga sputigena and Capnocytophaga gingivalis. The strain of Capnocytophaga ochracea was more sensitive to defensin-mediated bactericidal activity than either C. sputigena or C. gingivalis was. The three human defensins were equipotent in killing C. ochracea. C. ochracea was killed under aerobic and anaerobic conditions and over a broad pH range. Killing was most effective under hypotonic conditions but also occurred at physiologic salt concentrations. We concluded that Capnocytophaga spp. are sensitive to oxygen-independent killing by human defensins. Additional studies will be required to identify other components that may equip human neutrophils to kill A. actinomycetemcomitans, E. corrodens, and other oral gram-negative bacteria.

Blood Bactericidal Activity↗

PubMed1991

Antimicrobial activity of rabbit leukocyte defensins against Treponema pallidum subsp. pallidum.

Defensins, which are peptides with broad antimicrobial activity, are major constituents of rabbit neutrophils and certain macrophages. We tested six rabbit defensins, NP-1, NP-2, NP-3a, NP-3b, NP-4, and NP-5, for activity against Treponema pallidum subsp. pallidum. Mixtures of T. pallidum and defensin in 10% normal rabbit serum (NRS) or heat-inactivated NRS (HI-NRS) were incubated anaerobically for various time periods ranging between 0 and 16 h and then examined by dark-field microscopy for treponemal motility or inoculated intradermally into rabbits to assess treponemal virulence. Immobilization of T. pallidum by NP-1 (400 micrograms/ml) occurred after 4 and 8 h of coincubation in mixtures containing NRS and HI-NRS, respectively. Similarly, neutralization of T. pallidum by NP-1 occurred more rapidly and was complete when incubations were performed in NRS as compared with that in HI-NRS. Endpoint titration confirmed the augmentation of NP-1 antitreponemal activity by heat-labile serum factors; NP-1 showed neutralizing activity at 4 micrograms/ml (about 1 microM) in NRS and at 40 micrograms/ml in HI-NRS. When NP-1 was tested in serum that was deficient in C6, the T. pallidum neutralizing activity of NP-1 was reduced to levels slightly greater than that observed in HI-NRS. NP-1 that had been reduced and alkylated was inactive against T. pallidum. When NP-2, NP-3a, NP-3b, NP-4, and NP-5 were tested at 400 micrograms/ml, all exerted potent treponemicidal activity, manifested by abrogation or delayed development of cutaneous lesions relative to that of controls. These data suggest that defensins may equip certain macrophages and neutrophils to participate in host defense against T. pallidum, that the direct activity of defensins against T. pallidum is enhanced by heat-labile serum factors (presumably complement), and that conformational factors influence the biological activity of the defensin molecule.

Animals↗

PubMed1992

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.

Blood Bactericidal Activity↗

PubMed1991

Activated alpha 2-macroglobulin is a principal defensin-binding protein.

Defensins are highly abundant and variably cationic peptides that possess antimicrobial, cytotoxic, and chemoattractant properties and equip mammalian phagocytes for participation in host defense and inflammatory processes. We studied the binding of the human defensin HNP-1 by proteins in plasma and serum and identified activated (F-form) alpha 2-macroglobulin (alpha 2M) as a principal binding protein for HNP-1. In contrast, native (S-form) alpha 2M bound little HNP-1. The binding of HNP-1 by F-form alpha 2M was resistant to salt and boiling in 2% sodium dodecyl sulfate but was ablated by dithiothreitol. Pretreatment of methylamine-activated serum or plasma by iodoacetamide substantially decreased the binding of HNP-1 to alpha 2M, suggesting that thiol groups in activated alpha 2M play a role in defensin binding, possibly by covalently trapping defensins via thiol-disulfide exchange. Western blots of conventionally collected sera showed endogenous defensins complexed with the F-form of alpha 2M, indicating that the generation of defensin-alpha 2M complexes was not limited to the in vitro model of methylamine-activated serum or plasma and radiolabeled HNP-1. Previous studies indicated that native alpha 2M can be converted to its F-form by many proteases, including those released by neutrophils and platelets, and that the F-form is recognized and internalized by specific receptors on macrophages and hepatocytes. Our findings suggest that the alpha 2M system may function as a scavenger of defensins and other peptide mediators in inflamed tissues and may constitute an important mechanism for the regulation and containment of inflammation.

Blood Bactericidal Activity↗

PubMed1989

Interaction of human defensins with Escherichia coli. Mechanism of bactericidal activity.

Defensins are small, cysteine-rich antimicrobial peptides that are abundant in human, rabbit, and guinea pig neutrophils (PMN). Three defensins (human neutrophil peptide defensin [HNP]-1, HNP-2, and HNP-3) constitute between 30 and 50% of the total protein in azurophil granules of human PMN. We examined the mechanism of HNP-mediated bactericidal activity against Escherichia coli ML-35 (i-, y-, z+) and its pBR322-transformed derivative, E. coli ML-35p. Under conditions that supported bactericidal activity, HNP-1 sequentially permeabilized the outer membrane (OM) and inner membrane (IM) of E. coli. Coincident with these events, bacterial synthesis of DNA, RNA, and protein ceased and the colony count fell. Although these events were closely coupled under standard assay conditions, OM permeabilization was partially dissociated from IM permeabilization when experiments were performed with E. coli that had been plasmolyzed by mannitol. Under such conditions, the rate and extent of bacterial death more closely paralled loss of IM integrity than OM permeabilization. Electron microscopy of E. coli that had been killed by defensins revealed the presence of striking electron-dense deposits in the periplasmic space and affixed to the OM. Overall, these studies show that HNP-mediated bactericidal activity against E. coli ML-35 is associated with sequential permeabilization of the OM and IM, and that inner membrane permeabilization appears to be the lethal event.

Blood Bactericidal Activity↗

PubMed1989

Monocyte-chemotactic activity of defensins from human neutrophils.

We investigated the monocyte-chemotactic activity of fractionated extracts of human neutrophil granules. Monocyte-chemotactic activity was found predominantly in the defensin-containing fraction of the neutrophil granules. Purified preparations of each of the three human defensins (HNP-1, HNP-2, HNP-3) were then tested. HNP-1 demonstrated significant chemotactic activity for monocytes: Peak activity was seen at HNP-1 concentrations of 5 X 10(-9) M and was 49 +/- 20% (mean +/- SE, n = 9) of that elicited by 10(-8) M FMLP. HNP-2 (peak activity at 5 X 10(-9) M) was somewhat less active, yielding 19 +/- 10% (n = 11). HNP-3 failed to demonstrate chemotactic activity. Checkerboard analysis of monocyte response to HNP-1 and HNP-2 confirmed that their activity was chemotactic rather than chemokinetic. Neutrophils demonstrated a low level of response to defensins but this reaction was primarily chemokinetic. Defensins may play a role in the recruitment of monocytes by neutrophils into inflammatory sites.

Blood Proteins↗

PubMed1992

[Effects of human defensin HNP-1 on the production of tumor necrosis factor-alpha by human blood monocytes in vitro].

The influence of human defensin HNP-1 on the synthesis of tumor necrosis factor-alpha (TNF-alpha) by human blood monocytes was studied. It was shown that TNF-alpha production by human monocytes activated by SAC or PMA was augmented in the presence of HNP-1 concentrations of 10(-8)-10(-9) M. HNP-1 alone induced no synthesis of TNF-alpha. High concentration of HNP-1 (10(-4) M) was cytotoxic for human monocytes.

Blood Bactericidal Activity↗