Alteramide B is a microtubule antagonist of inhibiting Candida albicans

Background: Alteramide B (ATB), isolated from Lysobacter enzymogenes C3, was a new polycyclic tetramate macrolactam (PTM). ATB exhibited potent inhibitory activity against several yeasts, particularly Candida albicans SC5314, but its antifungal mechanism is unknown. Methods: The structure of ATB was established by extensive spectroscopic analyses, including high-resolution mass spectrometry, ID- and 2D-NMR, and CD spectra. Flow cytometry, fluorescence microscope, transmission electron microscope, molecular modeling, overexpression and site-directed mutation studies were employed to delineate the anti-Candida molecular mechanism of ATB. Results: ATB induced apoptosis in C albicans through inducing reactive oxygen species (ROS) production by disrupting microtubules. Molecular dynamics studies revealed the binding patterns of ATB to the p-tubulin subunit. Overexpression of the wild type and site-directed mutants of the (beta-tubulin gene (TUBB) changed the sensitivity of C albicans to ATB, confirming the binding of ATB to beta-tubulin, and indicating that the binding sites are 1215, L217, L273, L274 and R282. In vivo, ATB significantly improved the survival of the candidiasis mice and reduced fungal burden. Conclusion: The molecular mechanism underlying the ATB-induced apoptosis in C. albicans is through inhibiting tubulin polymerization that leads to cell cycle arrest at the G2/M phase. The identification of ATB and the study of its activity provide novel mechanistic insights into the mode of action of PTMs against the human pathogen. General significance: This study shows that ATB is a new microtubule inhibitor and a promising anti-Candida lead compound. The results also support beta-tubulin as a potential target for anti-Candida drug discovery. (C) 2016 Elsevier B.V. All rights reserved.