Structure, function, and evolution of Gga -AvBD11, the archetype of the structural avian-double-β-defensin family

Abstract

Out of the 14 avian β-defensins identified in theGallus gallusgenome, only 3 are present in the chicken egg, including the egg-specific avian β-defensin 11 (Gga-AvBD11). Given its specific localization and its established antibacterial activity,Gga-AvBD11 appears to play a protective role in embryonic development.Gga-AvBD11 is an atypical double-sized defensin, predicted to possess 2 motifs related to β-defensins and 6 disulfide bridges. The 3-dimensional NMR structure of the purifiedGga-AvBD11 is a compact fold composed of 2 packed β-defensin domains. This fold is the archetype of a structural family, dubbed herein as avian-double-β-defensins (Av-DBD). We speculate thatAvBD11emanated from a monodomain gene ancestor and that similar events might have occurred in arthropods, leading to another structural family of less compact DBDs. We show thatGga-AvBD11 displays antimicrobial activities against gram-positive and gram-negative bacterial pathogens, the avian protozoanEimeria tenella, and avian influenza virus.Gga-AvBD11 also shows cytotoxic and antiinvasive activities, suggesting that it may not only be involved in innate protection of the chicken embryo, but also in the (re)modeling of embryonic tissues. Finally, the contribution of either of the 2Gga-AvBD11 domains to these biological activities was assessed, using chemically synthesized peptides. Our results point to a critical importance of the cationic N-terminal domain in mediating antibacterial, antiparasitic, and antiinvasive activities, with the C-terminal domain potentiating the 2 latter activities. Strikingly, antiviral activity in infected chicken cells, accompanied by marked cytotoxicity, requires the full-length protein.

Antimicrobial peptides: mechanism of action, activity and clinical potential

“…For instance, the insect defensin A, has an α-helix of 11 amino acids in the middle (residues 14–24), and its N-terminal β-hairpin is parallel to the α-helix with a cyclic structure formed by the first 13 amino acid residues [ 103 ]. The antibacterial and antiparasitic activities are predominantly mediated by the N-terminal domain of the chicken Gga-AvBD11 and enhanced by its C-terminal domain while the antiviral activity requires the full-length protein [ 104 ]. The θ-defensins are the end-to-end cyclized tetracyclic peptides that have three disulfide bridges to connect their antiparallel β-sheets [ 105 ].…”

Antimicrobial Proteins and Peptides in Avian Eggshell: Structural Diversity and Potential Roles in Biomineralization

“…However, the C-terminal domain of AvBD11 is much less basic (pI = 9.0) than the N-terminal domain (pI = 12.2). This may support that the fact that the N-terminal domain exhibits elevated antibacterial activity compared to the C-terminal domain ( 88 ).…”

“…However, the C-terminal domain of AvBD11 is much less basic (pI = 9.0) than the N-terminal domain (pI = 12.2). This may support that the fact that the N-terminal domain exhibits elevated antibacterial activity compared to the Cterminal domain (88). All AvBDs, including those reported in the chicken eggshell proteome (AvBD9, AvBD10, AvBD11), possess antibacterial activities (91).…”

“…Although their 3D structure has not yet been solved, AvBD9 and AvBD10 are predicted to adopt the fold and disulfide-bridge topology of β-defensins. AvBD11 (82 amino acids, 9.3 kDa for the mature form) is unique among bird defensins as it consists of two β-defensin domains ( Figure 4A , left panel) ( 88 , 89 ). Chicken AvBD11 is the archetype of the structural avian double β-defensin family and such a double-β-defensin has never been identified in mammals, yet.…”

“…Recombinant chicken AvBD9 and AvBD10 display bactericidal activities against E. coli (Gram-negative) and Enterococcus faecalis (Gram-positive), and the tryptophan residue located at the C-terminal end of AvBD9 contributes to its bactericidal potency ( 93 ). Purified chicken AvBD11 binds heparin, and possesses antimicrobial activity against various microorganisms including bacteria (Gram-positive and Gram-negative), Eimeria tenella sporozoites and H1N1 influenza virus ( 38 , 88 , 89 ). This double β-defensin also has inhibitory effects on cell growth and/or cell migration ( 88 ).…”