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Zou G, de Leeuw E, Li C, Pazgier M, Li C, Zeng P, Lu WY, Lubkowski J, Lu W. Toward Understanding the Cationicity of Defensins. J Biol Chem 2007; 282:19653-65. [PMID: 17452329 DOI: 10.1074/jbc.m611003200] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Human defensins are a family of small antimicrobial proteins found predominantly in leukocytes and epithelial cells that play important roles in the innate and adaptive immune defense against microbial infection. The most distinct molecular feature of defensins is cationicity, manifested by abundant Arg and/or Lys residues in their sequences. Sequence analysis indicates that Arg is strongly selected over Lys in alpha-defensins but not in beta-defensins. To understand this Arg/Lys disparity in defensins, we chemically synthesized human alpha-defensin 1 (HNP1) and several HNP1 analogs where three Arg residues were replaced by each of the following six alpha-amino acids: Lys, ornithine (Orn), diaminobutyric acid (Dab), diaminopropionic acid (Dap), N,N-dimethyl-Lys ((diMe)Lys), and homo-Arg ((homo)Arg). In addition, we prepared human beta-defensin 1 (hBD1) and (Lys-->Arg)hBD1 in which all four Lys residues were substituted for Arg. Bactericidal activity assays revealed the following. 1) Arg-containing HNP1 and (Lys-->Arg)hBD1 are functionally better than Lys-HNP1 and hBD1, respectively; the difference between Arg and Lys is more evident in the alpha-defensin than in the beta-defensin and is more evident at low salt concentrations than at high salt concentrations. 2) For HNP1, the Arg/Lys disparity is much more pronounced with Staphylococcus aureus than with Escherichia coli, and the Arg-rich HNP1 kills bacteria faster than its Lys-rich analog. 3) Arg and Lys appear to have optimal chain lengths for bacterial killing as shortening Lys or lengthening Arg in HNP1 invariably becomes functionally deleterious. Our findings provide insights into the Arg/Lys disparity in defensins, and shed light on the cationicity of defensins with respect to their antimicrobial activity and specificity.
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Affiliation(s)
- Guozhang Zou
- Institute of Human Virology, University of Maryland Biotechnology Institute, Baltimore, Maryland 21201, USA
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Wu Z, Li X, Ericksen B, de Leeuw E, Zou G, Zeng P, Xie C, Li C, Lubkowski J, Lu WY, Lu W. Impact of pro segments on the folding and function of human neutrophil alpha-defensins. J Mol Biol 2007; 368:537-49. [PMID: 17355880 PMCID: PMC2754399 DOI: 10.1016/j.jmb.2007.02.040] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2006] [Revised: 01/26/2007] [Accepted: 02/11/2007] [Indexed: 01/15/2023]
Abstract
Human neutrophil alpha-defensins (HNPs) are synthesized in vivo as inactive precursor proteins, i.e. preproHNPs. A series of sequential proteolytic events excise the N-terminal inhibitory pro peptide, leading to defensin maturation and storage in azurophilic granules. The anionic pro peptide, required for correct sub-cellular trafficking and sorting of proHNPs, inhibits the antimicrobial activity of cationic defensins, either inter or intra-molecularly, presumably through charge neutralization. To better understand the role of the pro peptide in the folding and functioning of alpha-defensins and/or pro alpha-defensins, we chemically attached the proHNP1 pro peptide or (wt)pro peptide and the following artificial pro segments to the N terminus of HNP1: polyethylene glycol (PEG), Arg(10) (polyR), Ser(10) (polyS), and (cr)pro peptide, a charge-reversing mutant of the pro peptide where Arg/Lys residues were changed to Asp, and Asp/Glu residues to Lys. Comparative in vitro folding suggested that while all artificial pro segments chaperoned defensin folding, with PEG being the most efficient, the pro peptide catalyzed the folding of proHNPs likely through two independent mechanisms: solubilization of and interaction with the C-terminal defensin domain. Further, the N-terminal artificial pro segments dramatically altered the bactericidal activity of HNP1 against both Escherichia coli and Staphylococcus aureus. Surprisingly, (cr)pro peptide and (wt)pro peptide showed similar properties with respect to intra-molecular and inter-molecular catalysis of defensin folding as well as alpha-defensin binding, although their binding modes appeared different. Our findings identify a dual chaperone activity of the pro peptide and may shed light on the molecular mechanisms by which pro alpha-defensins fold in vivo.
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Affiliation(s)
- Zhibin Wu
- Institute of Human Virology, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201
| | - Xiangqun Li
- Institute of Human Virology, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201
| | - Bryan Ericksen
- Institute of Human Virology, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201
| | - Erik de Leeuw
- Institute of Human Virology, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201
| | - Guozhang Zou
- Institute of Human Virology, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201
| | - Pengyun Zeng
- Fudan-PharmCo Drug Target Research Center, School of Pharmacy, Fudan University, Shanghai 200032, China
| | - Cao Xie
- Institute of Human Virology, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201
- Fudan-PharmCo Drug Target Research Center, School of Pharmacy, Fudan University, Shanghai 200032, China
| | - Cong Li
- Fudan-PharmCo Drug Target Research Center, School of Pharmacy, Fudan University, Shanghai 200032, China
| | - Jacek Lubkowski
- Macromolecular Assembly Structure and Cell Signaling Section, NCI, National Institutes of Health, Frederick, MD 21702
| | - Wei-Yue Lu
- Fudan-PharmCo Drug Target Research Center, School of Pharmacy, Fudan University, Shanghai 200032, China
| | - Wuyuan Lu
- Institute of Human Virology, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201
- Author to whom correspondence should be addressed: Wuyuan Lu, , Tel: (410)706-4980, Fax: (410)706-7583
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Horng JC, Kotch FW, Raines RT. Is glycine a surrogate for a D-amino acid in the collagen triple helix? Protein Sci 2006; 16:208-15. [PMID: 17189476 PMCID: PMC2203290 DOI: 10.1110/ps.062560107] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Collagen is the most abundant protein in animals. Every third residue in a collagen strand is a glycine with phi, psi = -70 degrees, 175 degrees. A recent computational study suggested that replacing these glycine residues with D-alanine or D-serine would stabilize the collagen triple helix. This hypothesis is of substantial importance, as the glycine residues in collagen constitute nearly 10% of the amino acid residues in humans. To test this hypothesis, we synthesized a series of collagen mimic peptides that contain one or more D-alanine or D-serine residues replacing the canonical glycine residues. Circular dichroism spectroscopy and thermal denaturation experiments indicated clearly that the substitution of glycine with D-alanine or D-serine greatly disfavors the formation of a triple helix. Host-guest studies also revealed that replacing a single glycine residue with D-alanine is more destabilizing than is its replacement with L-alanine, a substitution that results from a common mutation in patients with collagen-related diseases. These data indicate that the glycine residues in collagen are not a surrogate for a D-amino acid and support the notion that the main-chain torsion angles of a glycine residue in the native structure (especially, phi > 0 degrees ) are critical determinants for its beneficial substitution with a D-amino acid in a protein.
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Affiliation(s)
- Jia-Cherng Horng
- Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, WI 53706, USA
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Abstract
BACKGROUND Defensins are antimicrobial peptides of innate immunity functioning by non-specific binding to anionic phospholipids in bacterial membranes. Their cationicity, amphipathicity and ability to oligomerize are considered key factors for their action. Based on structural information on human beta-defensin 2, we examine homologous defensins from various mammalian species for conserved functional physico-chemical characteristics. RESULTS Based on homology greater than 40%, structural models of 8 homologs of HBD-2 were constructed. A conserved pattern of electrostatics and dynamics was observed across 6 of the examined defensins; models backed by energetics suggest that the defensins in these 6 organisms are characterized by dimerization-linked enhanced functional potentials. In contrast, dimerization is not energetically favoured in the sheep, goat and mouse defensins, suggesting that they function efficiently as monomers. CONCLUSION Beta-defensin 2 from some mammals may work as monomers while those in others, including humans, work as oligomers. This could potentially be used to design human defensins that may be effective at lower concentrations and hence have therapeutic benefits.
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Affiliation(s)
- Anita Suresh
- Biomolecular Modelling and Design Group, Bioinformatics Institute, 30 Biopolis Street, #07-01 Matrix, Singapore 138671
| | - Chandra Verma
- Biomolecular Modelling and Design Group, Bioinformatics Institute, 30 Biopolis Street, #07-01 Matrix, Singapore 138671
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Yount NY, Waring AJ, Gank KD, Welch WH, Kupferwasser D, Yeaman MR. Structural correlates of antimicrobial efficacy in IL-8 and related human kinocidins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2006; 1768:598-608. [PMID: 17208195 DOI: 10.1016/j.bbamem.2006.11.011] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Received: 08/09/2006] [Revised: 10/18/2006] [Accepted: 11/13/2006] [Indexed: 01/21/2023]
Abstract
Chemokines are small (8-12 kDa) effector proteins that potentiate leukocyte chemonavigation. Beyond this role, certain chemokines have direct antimicrobial activity against human pathogenic organisms; such molecules are termed kinocidins. The current investigation was designed to explore the structure-activity basis for direct microbicidal activity of kinocidins. Amino acid sequence and 3-dimensional analyses demonstrated these molecules to contain iterations of the conserved gamma-core motif found in broad classes of classical antimicrobial peptides. Representative CXC, CC and C cysteine-motif-group kinocidins were tested for antimicrobial activity versus human pathogenic bacteria and fungi. Results demonstrate that these molecules exert direct antimicrobial activity in vitro, including antibacterial activity of native IL-8 and MCP-1, and microbicidal activity of native IL-8. To define molecular determinants governing its antimicrobial activities, the IL-8 gamma-core (IL-8gamma) and alpha-helical (IL-8alpha) motifs were compared to native IL-8 for antimicrobial efficacy in vitro. Microbicidal activity recapitulating that of native IL-8 localized to the autonomous IL-8alpha motif in vitro, and demonstrated durable microbicidal activity in human blood and blood matrices ex vivo. These results offer new insights into the modular architecture, context-related deployment and function, and evolution of host defense molecules containing gamma-core motifs and microbicidal helices associated with antimicrobial activity.
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Affiliation(s)
- Nannette Y Yount
- Division of Infectious Diseases, LAC-Harbor UCLA Medical Center, Torrance, CA 90509, USA
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Szyk A, Wu Z, Tucker K, Yang D, Lu W, Lubkowski J. Crystal structures of human alpha-defensins HNP4, HD5, and HD6. Protein Sci 2006; 15:2749-60. [PMID: 17088326 PMCID: PMC2242434 DOI: 10.1110/ps.062336606] [Citation(s) in RCA: 159] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Six alpha-defensins have been found in humans. These small arginine-rich peptides play important roles in various processes related to host defense, being the effectors and regulators of innate immunity as well as enhancers of adoptive immune responses. Four defensins, called neutrophil peptides 1 through 4, are stored primarily in polymorphonuclear leukocytes. Major sites of expression of defensins 5 and 6 are Paneth cells of human small intestine. So far, only one structure of human alpha-defensin (HNP3) has been reported, and the properties of the intestine defensins 5 and 6 are particularly poorly understood. In this report, we present the high-resolution X-ray structures of three human defensins, 4 through 6, supplemented with studies of their antimicrobial and chemotactic properties. Despite only modest amino acid sequence identity, all three defensins share their tertiary structures with other known alpha- and beta-defensins. Like HNP3 but in contrast to murine or rabbit alpha-defensins, human defensins 4-6 form characteristic dimers. Whereas antimicrobial and chemotactic activity of HNP4 is somewhat comparable to that of other human neutrophil defensins, neither of the intestinal defensins appears to be chemotactic, and for HD6 also an antimicrobial activity has yet to be observed. The unusual biological inactivity of HD6 may be associated with its structural properties, somewhat standing out when compared with other human alpha-defensins. The strongest cationic properties and unique distribution of charged residues on the molecular surface of HD5 may be associated with its highest bactericidal activity among human alpha-defensins.
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Affiliation(s)
- Agnieszka Szyk
- Macromolecular Assembly Structure and Cell Signaling Section, National Cancer Institute, Frederick, Maryland 21702, USA
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Rosengren KJ, Daly NL, Fornander LM, Jönsson LMH, Shirafuji Y, Qu X, Vogel HJ, Ouellette AJ, Craik DJ. Structural and Functional Characterization of the Conserved Salt Bridge in Mammalian Paneth Cell α-Defensins. J Biol Chem 2006; 281:28068-78. [PMID: 16857681 DOI: 10.1074/jbc.m604992200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
alpha-Defensins are mediators of mammalian innate immunity, and knowledge of their structure-function relationships is essential for understanding their mechanisms of action. We report here the NMR solution structures of the mouse Paneth cell alpha-defensin cryptdin-4 (Crp4) and a mutant (E15D)-Crp4 peptide, in which a conserved Glu(15) residue was replaced by Asp. Structural analysis of the two peptides confirms the involvement of this Glu in a conserved salt bridge that is removed in the mutant because of the shortened side chain. Despite disruption of this structural feature, the peptide variant retains a well defined native fold because of a rearrangement of side chains, which result in compensating favorable interactions. Furthermore, salt bridge-deficient Crp4 mutants were tested for bactericidal effects and resistance to proteolytic degradation, and all of the variants had similar bactericidal activities and stability to proteolysis. These findings support the conclusion that the function of the conserved salt bridge in Crp4 is not linked to bactericidal activity or proteolytic stability of the mature peptide.
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Affiliation(s)
- K Johan Rosengren
- Department of Chemistry and Biomedical Sciences, University of Kalmar, SE-391 82 Kalmar, Sweden.
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Wu Z, Li X, de Leeuw E, Ericksen B, Lu W. Why Is the Arg5-Glu13 Salt Bridge Conserved in Mammalian α-Defensins? J Biol Chem 2005; 280:43039-47. [PMID: 16246847 DOI: 10.1074/jbc.m510562200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Mammalian alpha-defensins, expressed primarily in leukocytes and epithelia, kill a broad range of microbes, constituting one of the first lines of innate immune defense against infection. Nine amino acid residues, including six cysteines, one glycine, and a pair of oppositely charged residues Arg/Glu, are conserved in the otherwise diverse sequences of all known mammalian alpha-defensins. Structural analysis indicates that the two charged residues form a salt bridge, likely stabilizing a protruding loop in the molecule. To investigate the structural and functional roles of the conserved Arg5-Glu13 salt bridge in alpha-defensins, we chemically prepared human neutrophil alpha-defensin 2 (HNP2) and five HNP2 analogs, R5E/E13R, E13Q, E13R, R5T/E13Y, and R14A. In contrast to HNP2 and R14A-HNP2, none of the four salt bridge analogs was capable of folding into a native conformation in the context of isolated defensin domains. However, when covalently attached to the 45-residue pro-HNP2 propeptide, the salt bridge analogs of HNP2 in their pro-forms all folded productively, suggesting that the Arg5-Glu13 salt bridge is not required for correct pro-alpha-defensin folding. When assayed against both Escherichia coli and Staphylococcus aureus, the six alpha-defensins showed bactericidal activity that correlated with the number of net positive charges carried by individual molecules in the panel, irrespective of whether or not the Arg5-Glu13 salt bridge was decimated, suggesting that Arg5 and Glu13 are not functionally conserved. Proteolytic resistance analysis with human neutrophil elastase, one major protease contained in azurophils with HNPs, revealed that destabilization of the salt bridge dramatically accelerated defensin degradation by the enzyme. Thus, we propose that the Arg5-Glu13 salt bridge found in most mammalian alpha-defensins is conserved for defensin in vivo stability.
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Affiliation(s)
- Zhibin Wu
- Institute of Human Virology, University of Maryland Biotechnology Institute, Baltimore, Maryland 21201, USA
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Xie C, Zeng P, Ericksen B, Wu Z, Lu WY, Lu W. Effects of the terminal charges in human neutrophil alpha-defensin 2 on its bactericidal and membrane activity. Peptides 2005; 26:2377-83. [PMID: 16009464 DOI: 10.1016/j.peptides.2005.06.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2005] [Revised: 06/01/2005] [Accepted: 06/01/2005] [Indexed: 12/19/2022]
Abstract
Human neutrophil alpha-defensin 2 (HNP2) was N-terminally acetylated and/or C-terminally amidated, resulting in three terminally modified analogs, Ac-HNP2, HNP2-NH2 and Ac-HNP2-NH2. We examined their bactericidal activity against E. coli and S. aureus and their ability to induce leakage from large unilamellar vesicles. Loss of the N-terminal positive charge was functionally deleterious, whereas removal of the C-terminal negative charge enhanced microbial killing and membrane permeabilization. Our findings validate the importance of electrostatic forces in defensin-microbe interactions and point to the bacterial cytoplasmic membrane as a target of HNP2 activity.
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Affiliation(s)
- Cao Xie
- Institute of Human Virology, University of Maryland Biotechnology Institute, 725 West Lombard Street, Baltimore, MD 21201, USA
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