Mammals generate a diverse array of antimicrobial proteins, largely represented by defensins or cathelicidins. The direct in vitro microbicidal activity of antimicrobial proteins has long been considered an important innate immune defense, although the in vivo relevance has only very recently been established for certain defensins and cathelicidins. Mammalian defensins and cathelicidins have also been shown to have multiple receptor-mediated effects on immune cells. Beta-defensins interact with CCR6; murine beta-defensin-2 in addition activates TLR4. Cathelicidins act on FPRL1-expressing cells. Furthermore, several defensins have considerable immunoenhancing activity. Thus, it appears that mammalian antimicrobial proteins contribute to both innate and adaptive antimicrobial immunity.
Previous studies have demonstrated that beta-defensins exhibit chemotactic activity by sharing the chemokine receptor CCR6 with the CC chemokine ligand CCL20/macrophage-inflammatory protein-3alpha (MIP-3alpha). Structural analysis of CCL20/MIP-3alpha revealed that most of the positively charged residues are concentrated at one area of its topological surface, a characteristic considered to be important for the antimicrobial activity of defensins. Here, we report that similar to defensins, CCL20/MIP-3alpha has antimicrobial effects on Escherichia coli, Pseudomonas aeruginosa, Moraxella catarrhalis, Streptococcus pyogenes, Enterococcus faecium, Staphylococcus aureus, and Candida albicans. Additionally, by screening a total of 30 human chemokines, we have identified an additional 17 human chemokines, which exhibit antimicrobial activity in vitro. Collectively, about two-thirds of the chemokines investigated so far has the capacity to kill microorganisms in vitro, suggesting that antimicrobial activity may be another host-defense function for certain chemokines. Comparison of the structural characteristics between antimicrobial and nonantimicrobial chemokines suggests that topological formation of a large, positively charged electrostatic patch on the surface of the molecule is likely to be a common structural feature of antimicrobial chemokines.
Human defensins form a family of small, cationic, and Cys-rich antimicrobial proteins that play important roles in innate immunity against invading microbes. They also function as effective immune modulators in adaptive immunity by selectively chemoattracting T lymphocytes and immature dendritic cells. On the basis of sequence homology and the connectivity of six conserved Cys residues, human defensins are classified into ␣ and  families. Structures of several -defensins have recently been characterized, confirming the disulfide connectivity conserved within the family, i.e., Cys 1 -Cys 5 , Cys 2 -Cys 4 , and Cys 3 -Cys 6 . We found that human -defensin 3 (hBD3), a recently described member of the growing  family, did not fold preferentially into a native conformation in vitro under various oxidative conditions. Using the orthogonal protection of Cys 1 -Cys 5 and of Cys 1 -Cys 6 , we chemically synthesized six topological analogs of hBD3 with predefined disulfide connectivities, including the (presumably) native  pairing. Unexpectedly, all differently folded hBD3 species exhibited similar antimicrobial activity against Escherichia coli, whereas a wide range of chemotactic activities was observed with these analogs for monocytes and cells transfected by the chemokine receptor CCR6. Furthermore, whereas substitution of all Cys residues by ␣-aminobutyric acid completely abolished the chemotactic activity of hBD3, the bactericidal activity remained unaffected in the absence of any disulfide bridge. Our findings demonstrate that disulfide bonding in hBD3, although required for binding and activation of receptors for chemotaxis, is fully dispensable for its antimicrobial function, thus shedding light on the mechanisms of action for human -defensins and the design of novel peptide antibiotics.
The last decade led to the discovery and characterization of several human beta-defensins. Analysis of genomic information indicates that the number of beta-defensin-like molecules encoded by the human genome may number in the tens. Growing interest in beta-defensins steadily enhances our knowledge about various aspects of their gene location, expression patterns and the transcription factors involved in their regulation in vivo. The hallmark property of beta-defensins, their antimicrobial activity, is clearly only the tip of the iceberg in the extensive network of inter-relations within the immune system in which these peptides function. Structural studies of beta-defensins provide the molecular basis for a better understanding of their properties, functions and their potential for practical applications. In this review, we present some recent advances in the studies of human beta-defensins, with an emphasis on possible correlations between their structural and functional properties.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.