Identification of a Glycosyltransferase Capable of Modifying a Second Site on the Amphotericin B Macrolactone

Many species of actinomycete bacteria synthesise glycosylated polyene macrolides that have potential as antifungal drugs. The sugar residues of these compounds have profound effects on potency, toxicity and water-solubility. The medically important antibiotics amphotericin B and nystatin A1 have a single D-mycosamine sugar on C19 of the polyene macrolactone. A few naturally occurring polyenes have a second sugar residue. This may be attached to C35 of 38-membered macrolactones like nystatins or to the equivalent C27 of 30-membered pentaenes like selvamicin. The recently discovered mandimycin has a C35 disaccharide that changes the mode of action, reduces adverse side effects, and delays the emergence of resistance in laboratory cultures of fungal pathogens. Glycosyltransferases that can modify the C27 and C35 positions are of interest to synthetic biologists. The GloSV enzyme is predicted to add a 2,6-dideoxy-D-hexose to C27 of a pentaene in Saccharopolyspora gloriosae. Here we assess GloSV in strains of the amphotericin producer, Streptomyces nodosus. Low levels of new amphotericin analogues modified with D-oliose or D-digitoxose were identified through HR-LCMS. The identification of this glycosyltransferase will assist the development of streptomycete systems for production of non-toxic polyene glycoanalogues.