Characterization and Antimicrobial Activity of the Teleost Chemokine CXCL20b

Abstract

Fish are a potential source of diverse organic compounds with a broad spectrum of biological activities. Many fish-derived antimicrobial peptides and proteins are key components of the fish innate immune system. They are also potential candidates for development of new antimicrobial agents. CXCL20b is a grass carp (Ctenopharyngodon idella) CXC chemokine strongly transcribed at the early stage of bacterial infections, for which the immune role had not been reported to date. In the present study, we found that CXCL20b is a cationic amphipathic protein that displays potent antimicrobial activity against both Gram-positive and Gram-negative bacteria. The results of DiOC2(3) and atomic force microscopy (AFM) assays indicated that CXCL20b could induce bacterial membrane depolarization and disruption in a short time. By performing further structure-activity studies, we found that the antimicrobial activity of CXCL20b was mainly relative to the N-terminal random coil region. The central part of this cytokine representing β-sheet region was insoluble in water and the C-terminal α-helical region did not show an antimicrobial effect. The results presented in this article support the poorly understood function of CXCL20b, which fulfills an important role in bony fish antimicrobial immunity.

CXCL20a, a Teleost-Specific Chemokine That Orchestrates Direct Bactericidal, Chemotactic, and Phagocytosis-Killing–Promoting Functions, Contributes to Clearance of Bacterial Infections

“…The cationic and amphipathic properties of APMs contribute to the antimicrobial function (21). By contrast, CiCXCL20b, a homolog of CiCXCL20a, owns a bactericidal activity (10), exhibits cationic patchy surface and amphipathic structure (Fig. 1D).…”

“…Expression and purification of CXCL20 members were performed as described previously (10). Briefly, sequences encoding CiCXCL20a, CiCXCL20b, and DrCXCL20 were inserted into pET-32a and transformed into E. coli BL21(DE3) TrxB (Invitrogen) to produce fusion protein, respectively.…”

“…The latter are induced by a number of pathogenic infections or inflammatory responses, promote leukocyte differentiation, and regulate the immune responses. Several chemokines have been reported to exert direct antimicrobial activity in mammals (8); however, only a few chemokines are reported to possess direct antibacterial activity in teleosts, such as rainbow trout CK11 and grass carp CXCL20b (9,10). In the previous reports, teleost chemokines exert antibacterial activity by inducing antimicrobial peptides or mediating inflammatory responses (11,12).…”

Innate Immunity

“…We list the most recent findings within functional chemokine research. It has been shown that grass carp cxcl20b possessed antibacterial activity by attaching to the bacterial membrane (Xiao et al 2020). In another study, it was shown that common carp Cxcb1 stimulated neutrophil extracellular trap formation-which was suggested to be an antipathogenic event (Pijanowski et al 2020).…”

Genome‐wide identification of catfish antimicrobial peptides: A new perspective to enhance fish disease resistance

“…CXCL11.3 and CXCL20.3 were two potential molecular markers for ESC resistance after ESC infection, while CXCL20.2 was suggestive as a molecular marker for columnaris infection 88 . Recently, CXCL20a/b in grass carp ( Ctenopharyngodon idella ) has been demonstrated to have potent antimicrobial activity in vitro and in vivo , and oral administration of CXCL20a nanopeptide can efficiently prevent bacterial infection in fish 89–91 . Such diversity in chemokine molecules may provide enriched resource for discovery of new AMPs and attract more interest towards exploration of this gene family as immune regulators.…”