Metabolic Engineeringand Combinatorialbiosynthesis Studies Of Polyoxinand Nikkomycin

Polyoxins and nikkomycins are specific chitin-synthase inhibitors, theyhave displayed a wide spectrum of antifungal activity and are low toxic toplants and animals. They are similar in chemical structure, both of themconsist of a nucleoside core and one or two independent peptidyl moietiesattached to the core at different sites. In addition, the biosynthetic genes ofpolyoxin and nikkomycin are highly homologous to each other. Basing onthese facts, we designed four polyoxin-nikkomycin hybrid antibiotics.We firstly cloned the biosynthetic gene cluster of nikkomycin fromStreptomyces tendae. On the basis of the structures of hybrid antibiotics, thespecific nikkomycin biosynthetic genes were inactivated by PCR-targeting,the mutated cosmids was introduced and heterologously expressed in amodified industrial polyoxin producer by conjugation. Several recombinantswere obtained by redesigning the biosynthetic pathway of the antibioticproducer.The fermentation broth of recombinants was purified and analyzed byMS and NMR, confirming the generation of four objective hybrid peptidylnucleoside antibiotics (polyoxin N, nikkoxin B, nikkoxin C and nikkoxin D).All of the hybrid antibiotics in this study have effectively inhibited mosttested human or plant fungal pathogens. Among them, nikkoxin D was significantly more potent against human fungal pathogens Trichosporoncutaneum than natural antibiotics which have potential clinical applicationvalues. This study has provided a good example for the rational redesign ofthe current biosynthetic pathways with the strategy of metabolic engineeringand combinatorial biosynthesis for generating more novel peptidyl nucleosideantibiotics.