Antimicrobial and host cell-directed activities of Gly/Ser-rich peptides from salmonid cathelicidins

Abstract

OriginalAntimicrobial and host cell-directed activities of Gly/Ser-rich peptides from salmonid cathelicidins This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 3Highlights 38• Salmonid cathelicidin-derived peptides show medium-sensitive antimicrobial activity 39• They are not cytotoxic to fish cells and promote proliferation of trout fibroblasts 40• Peptide STF(1-37) potentiates phagocytosis and respiratory burst in trout leukocytes 41• STF(1-37) and β-glucan act synergistically to immunostimulate trout leukocytes 42Cathelicidins, a major family of vertebrate antimicrobial peptides (AMPs), have a recognized role 44 in the first line of defense against infections. They have been identified in several salmonid species, 45 where the putative mature peptides are unusually long and rich in serine and glycine residues, often 46 arranged in short multiple repeats (RLGGGS/RPGGGS) intercalated by hydrophobic motifs. 47Fragments of 24 to 40 residues, spanning specific motifs and conserved sequences in grayling or 48 brown, rainbow and brook trout, were chemically synthesized and examined for antimicrobial 49 activity against relevant Gram-positive and Gram-negative salmonid pathogens, as well as 50 laboratory reference strains. They were not active in complete medium, but showed varying potency 51 and activity spectra in diluted media. Bacterial membrane permeabilization also occurred only 52 under these conditions and was indicated by rapid propidium iodide uptake in peptide-treated 53 bacteria. However, circular dichroism analyses indicated that they did not significantly adopt 54 ordered conformations in membrane-like environments. The peptides were not hemolytic or 55 cytotoxic to trout cells, including freshly purified head kidney leukocytes (HKL) and the 56 fibroblastic RTG-2 cell line. Notably, when exposed to them, HKL showed increased metabolic 57 activity, while a growth-promoting effect was observed on RTG-2 cells, suggesting a functional 58 interaction of salmonid cathelicidins with host cells similar to that shown by mammalian ones. The 59 three most active peptides produced a dose-dependent increase in phagocytic uptake by HKL 60 simultaneously stimulated with bacterial particles. The peptide STF(1-37), selected for further 61 analyses, also enhanced phagocytic uptake in the presence of autologous serum, and increased 62 intracellular killing of live E. coli. Furthermore, when tested on HKL in combination with the 63 immunostimulant β-glucan, it synergistically potentiated both phagocytic up...

Antimicrobial Peptides: Classification, Design, Application and Research Progress in Multiple Fields

“…These peptides contain 14% to 22% glycine residues, which have an important effect on the tertiary structure of the peptide chain. A glycine-rich AMP derived from salmonid cathelicidins activates phagocyte-mediated microbicidal mechanisms, which differ from the mechanism of conventional AMPs ( D’Este et al, 2016 ). Furthermore, the glycine-rich central–symmetrical GG3 is an ideal commercial drug candidate against clinical Gram-negative bacteria ( Wang et al, 2015 ).…”

Antimicrobial Peptides of Salmonid Fish: From Form to Function

“…Another rainbow trout-derived AMP, histone H2A, shows some hemolytic activity against rainbow trout erythrocytes beyond 0.3 µM [ 26 ]. Histone H2A is quite hydrophobic in nature, with a total hydrophobic ratio of 50% [ 27 ]. Albeit, even with a hydrophobicity ratio of 50%, it does not lead to complete hemolysis.…”

Immuno-Stimulatory Peptides as a Potential Adjunct Therapy against Intra-Macrophagic Pathogens

“…Fish cathelicidins also increase phagocytosis and respiratory burst of head kidney leukocytes. Moreover, these peptides are able to synergize with immunostimulant beta-glucans against E. coli infections [ 79 ]. Retrocyclins, humanized analogues of the teta-defensin peptides obtained from nonhuman primate leukocytes, were also able to bind to Bacillus anthracis , enhance phagocytosis and facilitate killing by RAW 264.7 macrophages [ 80 ].…”