Genetic Manipulation of the Pneumocandin Biosynthetic Pathway for Generation of Analogues and Evaluation of Their Antifungal Activity.

Pneumocandins are lipohexapeptides of the echinocandin family that potently interrupt fungal cell wall biogenesis by noncompetitive inhibition of 1,3-β-glucan synthase. The pneumocandin biosynthetic gene cluster was previously elucidated by whole genome sequencing. In addition to the core nonribosomal peptide synthetase and polyketide synthase (GLNRPS4 and GLPKS4), the pneumocandin biosynthetic cluster includes two P450-type hemeprotein monooxygenase genes (GLP450-1 and GLP450-2) and four nonheme mononuclear iron oxygenase genes (GLOXY1, GLOXY2, GLOXY3, and GLOXY4), which function to biosynthesize and create the unusual sequence of hydroxylated amino acids of the mature pneumocandin peptide. Insertional inactivation of three of these genes (GLP450-1, GLP450-2, and GLOXY1) generated 13 different pneumocandin analogues that lack one, two, three, or four hydroxyl groups on 4R,5R-dihydroxy-ornithine and 3S,4S-dihydroxy-homotyrosine of the parent hexapeptide. Among them, seven analogues are previously unreported genetically engineered pneumocandins whose structures were established by NMR experiments. These new pneumocandins afforded a unique opportunity for side-by-side exploration of the effects of hydroxylation on pneumocandin antifungal activity. All of these cyclic lipopeptides showed potent antifungal activities, and two new metabolites pneumocandins F (3) and G (4) were more potent in vitro against Candida species and Aspergillus fumigatus than the principal fermentation products, pneumocandins A0 and B0.