<i>cis</i>-9-Hexadecenal, a Natural Compound Targeting Cell Wall Organization, Critical Growth Factor, and Virulence of <i>Aspergillus fumigatus</i>

Abstract

<i>Aspergillus fumigatus</i> causes several nosocomial pulmonary infections and accounts for high morbidity and mortality rate globally. Among various virulence factors, 1,8-dihydroxynaphthalene-melanin plays an important role in the survival during unfavorable conditions both <i>in vivo</i> and <i>in vitro</i>, masks various molecular patterns associated with <i>A. fumigatus,</i> and protects it from the host immune system. In the present study, we aim to understand the potential of <i>cis</i>-9-hexadecenal as an antimelanogenic compound and its role in modulating other associated virulence factors in <i>A. fumigatus</i>. <i>cis</i>-9-Hexadecenal is a bioactive compound that belongs to C₁₆ mono-unsaturated fatty-aldehyde groups. Minimum effective concentration of <i>cis</i>-9-hexadecenal affecting <i>A. fumigatus</i> melanin biosynthesis was determined using broth microdilution method. The spectrophotometric analysis revealed reduced melanin content (91%) and hydrophobicity (59%) at 0.293 mM of <i>cis</i>-9-hexadecenal. Cell surface organizational changes using electron microscopy showed altered demelanized smooth <i>A. fumigatus</i> conidial surface without any protrusions after <i>cis</i>-9-hexadecenal treatment. The transcript analysis of polyketide synthase (PKS) <i>pksP</i>/<i>alb1</i> gene was quantified through qRT-PCR which revealed an upregulated expression. Total proteome profiling conducted through LC-MS-MS showed upregulated PKS enzyme but other downstream proteins involved in the 1,8-dihydroxynaphthalene-melanin biosynthesis pathway were absent. The homology modeling of PKS using Expasy's web server predicted that PKS is stable at varied conditions and is hydrophilic in nature. The Ramachandran plot by PROCHECK confirmed the 3-D structure of PKS to be reliable. Docking analysis using AutoDock-4.2.6 predicted the binding of <i>cis</i>-9-hexadecenal and PKS at Thr-264 and Ser-171 residue via hydrogen bonding at a low binding energy of -4.95 kcal/mol.