Immunology
A small mycobacteriophage-derived peptide and its improved isomer restrict mycobacterial infection via dual mycobactericidal-immunoregulatory activities

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Mycobacteriophages express various peptides/proteins to infect Mycobacterium tuberculosis (M. tb). Particular attention has been paid to mycobacteriophage-derived endolysin proteins. We herein characterized a small mycobacteriophage-derived peptide designated AK15 with potent anti-M. tb activity. AK15 adopted cationic amphiphilic α-helical structure, and on the basis of this structure, we designed six isomers with increased hydrophobic moment by rearranging amino acid residues of the helix. We found that one of these isomers, AK15-6, exhibits enhanced anti-mycobacterial efficiency. Both AK15 and AK15-6 directly inhibited M. tb by trehalose 6,6′-dimycolate (TDM) binding and membrane disruption. They both exhibited bactericidal activity, cell selectivity, and synergistic effects with rifampicin, and neither induced drug resistance to M. tb. They efficiently attenuated mycobacterial load in the lungs of M. tb-infected mice. We observed that lysine, arginine, tryptophan, and an α-helix are key structural requirements for their direct anti-mycobacterial action. Of note, they also exhibited immunomodulatory effects, including inhibition of proinflammatory response in TDM-stimulated or M. tb-infected murine bone marrow-derived macrophages (BMDMs) and M.tb-infected mice and induction of only a modest level of cytokine (tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6)) production in murine BMDMs and a T-cell cytokine (interferin-γ (IFN-γ) and TNF-α) response in murine lung and spleen. In summary, characterization of a small mycobacteriophage-derived peptide and its improved isomer revealed that both efficiently restrain M. tb infection via dual mycobactericidal-immunoregulatory activities. Our work provides clues for identifying small mycobacteriophage-derived anti-mycobacterial peptides and improving those that have cationic amphiphilic α-helices.

antimicrobial peptide (AMP)
peptides
structure-function
amino acid
drug action
drug resistance
α-helix
anti-mycobacterial peptide
hydrophobic moment
mycobacteriophage
antibiotic
endolysin
immune regulation
Mycobacterium tuberculosis

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This work was supported by National Natural Science Foundation of China Grants 81402830, 31870868, 81603080, 31670930, 31700656, and 81802023; China Postdoctoral Science Foundation Grant 2015M571815; Ministry of Science and Technology of China Grant 2018ZX10731301-001-006; Natural Science Foundation of Jiangsu Province Grant BK20140362 and Fujian Province Grant 2017J05050; Priority Academic Program Development of Jiangsu Higher Education Institutions; Program for Changjiang Scholars and Innovative Research Team in University Grant PCSIRTIRT1075; and Science and Technology Development of Suzhou Grants SNG2017050 and sys2018017. The authors declare that they have no conflicts of interest with the contents of this article.

This article contains Tables S1–S4 and Figs. S1–S8.

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These authors contributed equally to this work.

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The abbreviations used are:

    TB

    tuberculosis

    FIC

    fractional inhibitory concentration

    FICI

    fractional inhibitory concentration index

    Mt. b

    Mycobacterium tuberculosis

    MIC

    minimum inhibitory concentration

    RU

    resonance units

    sAK15

    scrambled AK15

    i.v.

    intravenous

    TDM

    trehalose 6,6′-dimycolate

    BMDM

    bone marrow-derived macrophage

    IFN

    interferon

    TNF

    tumor necrosis factor

    IL

    interleukin

    FBS

    fetal bovine serum

    TFE

    trifluoroethanol.