Purlisin, a toxin-like defensin derived from clinical pathogenic fungus Purpureocillium lilacinum with both antimicrobial and potassium channel inhibitory activities.

Abstract

Clinical fungal infections always cause a negative impact on human health. Moreover, during the interaction of pathogenic fungi with the environment and host, many biologically active substances are produced. Here, we report a new toxin-like defensin of purlisin derived from a clinical pathogenic isolate of Purpureocillium lilacinum. The analysis of its genomic and mRNA sequences revealed an open reading frame of 444bp without introns. The deduced precursor peptide was composed of 147 amino acids, and the mature peptide were identified at protein level by LC-ESI-Q-TOF-MS/MS. After posttranslational processing, the precursor peptide of purlisin was split into two independent peptides. The two mature defensins, purlisin-NT and purlisin-CT, are consisting of 36 and 38 amino acid residues, which can form three and four intramolecular disulfide bonds, respectively. The results of circular dichroism and homology modeling revealed that they adopted a representative cysteine-stabilized α-helical and β-sheet motif. The purlisin-NT showed a dose-dependent selective inhibition of immune-related hKv1.3 target channel with IC50 value of 0.2±0.04μM but no obvious antibacterial activity, while the purlisin-CT displayed antimicrobial activities against gram-positive bacteria as well as clinical isolates of MRSA and low affinities for potassium channels. Our findings suggest that purlisin-NT with immunosuppressive effects and purlisin-CT possessing antibacterial activities are adapted to the survival and pathogenicity of clinical P lilacinumis. Moreover, they can also be used as templates for the design of novel antibacterial peptide and immunosuppressive agents.