Structure, function, and evolution of Gga -AvBD11, the archetype of the structural avian-double-β-defensin family (original) (raw)
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Biology
Beta-defensins are an essential group of cysteine-rich host-defence peptides involved in vertebrate innate immunity and are generally monodomain. Among bird defensins, the avian β-defensin 11 (AvBD11) is unique because of its peculiar structure composed of two β-defensin domains. The reasons for the appearance of such ‘polydefensins’ during the evolution of several, but not all branches of vertebrates, still remain an open question. In this study, we aimed at exploring the origin and evolution of the bird AvBD11 using a phylogenetic approach. Although they are homologous, the N- and C-terminal domains of AvBD11 share low protein sequence similarity and possess different cysteine spacing patterns. Interestingly, strong variations in charge properties can be observed on the C-terminal domain depending on bird species but, despite this feature, no positive selection was detected on the AvBD11 gene (neither on site nor on branches). The comparison of AvBD11 protein sequences in differen...
BMC microbiology, 2016
Avian beta-defensins (AvBD) are small, cationic, antimicrobial peptides. The potential application of AvBDs as alternatives to antibiotics has been the subject of interest. However, the mechanisms of action remain to be fully understood. The present study characterized the structure-function relationship of AvBD-6 and AvBD-12, two peptides with different net positive charges, similar hydrophobicity and distinct tissue expression profiles. AvBD-6 was more potent than AvBD-12 against E. coli, S. Typhimurium, and S. aureus as well as clinical isolates of extended spectrum beta lactamase (ESBL)-positive E. coli and K. pneumoniae. AvBD-6 was more effective than AvBD-12 in neutralizing LPS and interacting with bacterial genomic DNA. Increasing bacterial concentration from 10(5) CFU/ml to 10(9) CFU/ml abolished AvBDs' antimicrobial activity. Increasing NaCl concentration significantly inhibited AvBDs' antimicrobial activity, but not the LPS-neutralizing function. Both AvBDs were mi...
Immunogenetics, 2007
Antimicrobial peptides (AMPs), essential components of innate immunity, are found in a range of phylogenetically diverse species and are thought to act by disrupting the membrane integrity of microbes. In this paper, we used evolutionary signatures to identify sites that are most relevant during the functional evolution of these molecules and introduced amino acid substitutions to improve activity. We first demonstrate that the anti-microbial activity of chicken avian β-defensin-8, previously known as gallinacin-12, can be significantly increased against Escherichia coli, Listeria monocytogenes, Salmonella typhimurium, Salmonella typhimurium phoP− mutant and Streptococcus pyogenes through targeted amino acid substitutions, which confer increased peptide charge. However, by increasing the AMP charge through amino acid substitutions at sites predicted to be subject to positive selection, antimicrobial activity against Escherichia coli was further increased. In contrast, no further increase in activity was observed against the remaining pathogens. This result suggests that chargeincreasing modifications confer increased broad-spectrum activity to an AMP, whilst positive selection at particular sites is involved in directing the antimicrobial response against specific pathogens. Thus, there is potential for the rational design of novel therapeutics based on specifically targeted and modified AMPs.
Journal of Biological Chemistry, 2014
Background: Ovodefensins are small peptides from eggs, related to avian antimicrobial defensins. Results: The first three-dimensional structure of ovodefensins (gallin) is solved, and its antimicrobial properties are screened. Conclusion: Gallin adopts a -defensin fold, with significant variations. Its antibacterial spectrum was restricted to E. coli. Significance: The first structural features may be related to E. coli specificity and/or other yet unknown functions. Gallin is a 41-residue protein, first identified as a minor component of hen egg white and found to be antimicrobial against Escherichia coli. Gallin may participate in the protection of the embryo during its development in the egg. Its sequence is related to antimicrobial -defensin peptides. In the present study, gallin was chemically synthesized 1) to further investigate its antimicrobial spectrum and 2) to solve its threedimensional NMR structure and thus gain insight into structurefunction relationships, a prerequisite to understanding its mode(s) of action. Antibacterial assays confirmed that gallin was active against Escherichia coli, but no additional antibacterial activity was observed against the other Gram-positive or Gram-negative bacteria tested. The three-dimensional structure of gallin, which is the first ovodefensin structure to have been solved to date, displays a new five-stranded arrangement. The gallin three-dimensional fold contains the three-stranded antiparallel -sheet and the disulfide bridge array typical of vertebrate -defensins. Gallin can therefore be unambiguously classified as a -defensin. However, an additional short two-stranded -sheet reveals that gallin and presumably the other ovodefensins form a new structural subfamily of -defensins. Moreover, gallin and the other ovodefensins calculated by homology modeling exhibit atypical hydrophobic surface properties, compared with the already known vertebrate -defensins. These specific structural features of gallin might be related to its restricted activity against E. coli and/or to other yet unknown functions. This work provides initial understanding of a critical sequencestructure-function relationship for the ovodefensin family.
Initial Insights into Structure-Activity Relationships of Avian Defensins
Journal of Biological Chemistry, 2011
Background: Avian defensins are antimicrobial peptides of a bird's immunity. Results: The target of chicken AvBD2 defensin is not chiral. Its structure is not amphipathic. The reduced and AvBD2-K31A forms dramatically decrease antibacterial activity. Conclusion: AvBD2 may disrupt the bacterial membrane through a nonchiral, nonspecific interaction. Significance: Knowledge of the structure-function relationships of avian defensins is a prerequisite for their use as alternatives to antibiotics. * The work was supported by "Biotechnocentre" Grant 3200068 from the Région Centre, France, by a doctoral fellowship from Institut National de la Recherche Agronomique and Région Centre, by a postdoctoral fellowship from CNRS. Financial support from the TGE RMN THC Fr3050 for conducting the research is gratefully acknowledged. □ S This article contains supplemental Figs. S1-S6 and Tables S1-S3.
Immunogenetics, 2005
Antimicrobial peptides are essential components of innate immunity and are generally thought to act by disrupting the membrane integrity of microbes. Here we report the discovery of two novel chicken β-defensins, gallinacin (Gal)-11 and Gal-12, found by hidden Markov model profile searching of the chicken genome. We have sequenced the genes and elucidated the 3′UTR of Gal-11. Differential mRNA expression of these novel genes has been shown across a panel of chicken tissues. Gal-11 mRNAwas highly expressed in the small intestine, the liver, the gall bladder and the spleen and also showed moderate expression in several other areas of the chicken anatomy, whilst Gal-12 mRNAwas found only in the liver and the gall bladder. Antimicrobial activity of synthetic Gal-11 has been demonstrated against a range of bacteria and is predominantly active against the intestinal pathogens Salmonella typhimurium and Listeria monocytogenes.
Molecular Evolutionary Analysis of a-Defensin Peptides in Vertebrates
Rajshahi University Journal of Science and Engineering, 2016
α-Defensin is a group of polypeptides with antimicrobial activity found in the host defense system and it is widely distributed in, but not limited to mammalian epithelial cells and phagocytes. These molecules protect the organism from a diverse spectrum of bacteria, viruses, fungi, and protozoan parasites. Different studies have revealed widesequence variation within α-defensin sequences, but the underlying evolutionary cause is not well-studied. In this study, the α-defensin gene from 25 vertebrate species has been comprehensively collected and computationally analyzed. NCBI gene and nucleotide databases were accessed to extract meta-information about α-defensin gene's defensin domain and leader propeptide sequences. Full coding sequences downloaded from nucleotide database by splitting out intron sequence. MEGA software used to construct phylogenetic tree using Neighbor-Joining method, which indicates that α-defensin gene evolution does not matches with species evolution. Sel...
Molecular Immunology, 2009
The cationic, cysteine-rich peptides called -defensins play a major role in the innate immune response. Here, we describe the identification and characterization of the duck -defensin-2 homologue, Anas platyrhynchos avian -defensin 2 (Apl AvBD2). The 195 base pair open reading frame (ORF) of Apl AvBD2 has 83% identity with Gga AvBD2 (chicken) and 85% identity with Mga AvBD2 (turkey) at nucleotide level. The gene corresponding to the coding region is comprised of three exons and two introns in both Apl AvBD2 and Gga AvBD2. The predicted secondary structure of Apl AvBD2 has the classical "defensin core motif" formed by the -sheet rich structure. Apart from mild expression in tissues like kidney, lung, brain, bursa of Fabricious and ovary, Apl AvBD2 mRNA show a very high level constitutive expression in bone marrow and spleen, indicating that it is a myeloid defensin. Purified recombinant Apl AvBD2 demonstrated in vitro antibacterial activity against both Gram-positive and Gram-negative bacteria, with a minimum bactericidal concentration (MBC) of 3.7 M against Micrococcus luteus NCIM 2871 and Escherichia coli NCIM 2685, and of 2.2 M against Reimerella anatipestifer. The immunomodulatory potential of Apl AvBD2 was shown by chemotaxis of DT-40 chicken B-lymphocytes. The widespread tissue distribution and the potent bactericidal and chemotactic activity make Apl AvBD2 an important molecule in the innate immune response in ducks. It may play a vital role in the immune response of these birds against bacterial and viral pathogens.
Evolution and Diversity of Defensins in Vertebrates
2017
Defensins are a large family of genes that were first characterised as encoding antimicrobial peptides, with a broad range of activity against viruses, bacteria and fungi. It is clear, however, that at least in vertebrates, they have acquired a variety of other roles in addition to direct antimicrobial activity, including cell signalling, reproduction and mammalian coat colour. In this article, we review the evolutionary history of the three types of defensins found in vertebrates, namely α-, β- and θ-defensins. We consider evolution at a deep timescale, where a pattern of duplication and divergence emerges, consistent with birth-and-death evolution. At a more recent timescale, we consider the evolutionary genetics of defensins within species, particularly copy number variation which is observed for many defensins across several lineages. The different functions of at least some defensins in different evolutionary lineages raise some problems in inferring function based on identific...