Key Determinants of Human α-Defensin 5 and 6 for Enhancement of HIV Infectivity.

Kimyata Valere,Wuyuan Lu,Theresa Chang

doi:10.3390/v9090244

Abstract

Defensins are antimicrobial peptides important for mucosal innate immunity. They exhibit a broad spectrum of activity against bacteria, viruses, and fungi. Levels of α-defensins are elevated at the genital mucosa of individuals with sexually transmitted infections (STIs). Somewhat paradoxically, human α-defensin 5 and 6 (HD5 and HD6) promote human immunodeficiency virus (HIV) infectivity, and contribute to STI-mediated enhancement of HIV infection in vitro. Specific amino acid residues of HD5 and HD6 that are crucial for antimicrobial activities have been characterized previously; however, the key determinants of defensins responsible for enhancement of HIV infectivity are not known. Here, we have identified residues of HD5 and HD6 that are required for enhancement of HIV attachment and infection. Most of these residues are involved in hydrophobicity and self-association of defensins. Specifically, we found that mutant defensins L16A-HD5, E21me-HD5, L26A-HD5, Y27A-HD5, F2A-HD6, H27W-HD6, and F29A-HD6 significantly lost their ability to promote HIV attachment and infection. L29A mutation also reduced HIV infection-enhancing activity of HD5. Additionally, a number of mutations in charged residues variably affected the profile of HIV attachment and infectivity. One HD5 charged mutation, R28A, notably resulted in a 34–48% loss of enhanced HIV infectivity and attachment. These results indicate that defensin determinants that maintain high-ordered amphipathic structure are crucial for HIV enhancing activity. In a comparative analysis of the mutant defensins, we found that for some defensin mutants enhancement of HIV infectivity was associated with the reverse transcription step, suggesting a novel, HIV attachment-independent, mechanism of defensin-mediated HIV enhancement.

Highlights

Defensins are antimicrobial peptides important for innate mucosal immunity.Individuals with sexually transmitted infections (STIs) have increased levels of defensins in genital secretions [4,5,6], suggesting a potential role of defensins in modulating human immunodeficiency virus (HIV) transmission
To identify the molecular determinants critical for HD5-mediated enhancement of HIV-1 infectivity, we examined the effect of a panel of HD5 mutants on HIV-1 infection
Wild type (WT) HD5 or HD5 mutants at 10 or 30 μg/mL were incubated with serum-free HIV-1JR-FL before adding the virus–defensin mixture to HeLa-CD4-CCR5 cells, and infection was assayed 48 h later

Summary

Introduction

Defensins are antimicrobial peptides important for innate mucosal immunity (reviewed in [1,2,3]).Individuals with sexually transmitted infections (STIs) have increased levels of defensins in genital secretions [4,5,6], suggesting a potential role of defensins in modulating human immunodeficiency virus (HIV) transmission. HD5 levels are increased in cervicovaginal lavage from women with bacterial vaginosis [4] and in urethral fluid from men infected with Chlamydia trachomatis or Neisseria gonorrhoeae [6] compared to individuals without STIs. HD5 and HD6 exhibit a broad spectrum of antimicrobial activities [9,10,11,12], we have previously shown that HD5 and HD6, Viruses 2017, 9, 244; doi:10.3390/v9090244 www.mdpi.com/journal/viruses. Knocking down HD5 or HD6 in vitro significantly reduces Neisseria gonorrhoeae-mediated enhancement of HIV infectivity [8]. These findings indicate that, in the setting of STIs, HIV may overcome the mucosal barrier by exploiting the increased levels of defensins produced by the host in response to bacterial pathogens

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Results

Conclusion