A Biomimetic Polymer for the Extraction and Purification of Superior Analogues of Amphotericin B.

Amphotericin B has been an essential drug in the fight against leishmaniasis and fungal pathogens for decades, and has more recently gained attention for the very limited microbial resistance displayed against it. However, its toxicity has restricted its use to only the most severe cases of disease, and attempts to reduce these ill effects via formulation have had only minor success. Genetic engineering has allowed the development of superior amphotericin analogues, notably 16-descarboxyl-16-methyl amphotericin B (MeAmB), which shows a ten-fold reduction in toxicity in addition to a slight improvement in therapeutic activity.

Engineered biosynthesis and characterisation of disaccharide-modified 8-deoxyamphoteronolides.

Several polyene macrolides are potent antifungal agents that have severe side effects. Increased glycosylation of these compounds can improve water solubility and reduce toxicity. Three extending glycosyltransferases are known to add hexoses to the mycosaminyl sugar residues of polyenes.

Role of polyol moiety of amphotericin B in ion channel formation and sterol selectivity in bilayer membrane.

Amphotericin B (AmB) is a polyene macrolide antibiotic widely used to treat mycotic infections. In this paper, we focus on the role of the polyol moiety of AmB in sterol selectivity using 7-oxo-AmB, 7α-OH-AmB, and 7β-OH-AmB. The 7-OH analogs were prepared from 7-oxo-AmB.

Engineered biosynthesis of disaccharide-modified polyene macrolides.

Recent work has uncovered genes for two glycosyltransferases that are thought to catalyze mannosylation of mycosaminyl sugars of polyene macrolides. These two genes are nypY from Pseudonocardia sp. strain P1 and pegA from Actinoplanes caeruleus.

Versatility of enzymes catalyzing late steps in polyene 67-121C biosynthesis.

Actinoplanes caeruleus produces 67-121C, a heptaene macrolide modified with a D-mannosyl-D-mycosaminyl disaccharide. Draft genome sequencing revealed genes encoding mycosaminyltransferase, mycosamine synthase, a cytochrome P450 that modifies the macrolactone core, and the extending mannosyltransferase. Only the mycosamine synthase and P450 were active in the biosynthesis of amphotericins in Streptomyces nodosus, the amphotericin producer.

Streptomyces nodosus host strains optimized for polyene glycosylation engineering.

The AmphDI glycosyltransferase transfers a mycosaminyl sugar residue from GDP onto 8-deoxyamphoteronolide B, the aglycone of the antifungal amphotericin B. In this study the amphDI gene was inactivated in Streptomyces nodosus strains lacking the AmphN cytochrome P450. The new mutants produced 8-deoxy-16-methyl-16-descarboxyl amphoteronolides in high yield.

A labile point in mutant amphotericin polyketide synthases.

Streptomyces nodosus produces the antifungal polyene amphotericin B. Numerous modifications of the amphotericin polyketide synthase have yielded new analogues. However, previous inactivation of the ketoreductase in module 10 resulted in biosynthesis of truncated polyketides.

Isolation and characterisation of amphotericin B analogues and truncated polyketide intermediates produced by genetic engineering of Streptomyces nodosus.

Amphotericin B is a powerful but toxic drug used against fungal infections and leishmaniases. These diseases would be treated more effectively if non-toxic amphotericin derivatives could be produced on a large scale at low cost. Genetic manipulation of the amphotericin B producer, Streptomyces nodosus, has previously led to the detection and partial characterisation of 8-deoxyamphotericin B, 16-descarboxyl-16-methyl-amphotericin B, 15-deoxy-16-descarboxyl-16-methyl-15-oxo-amphotericin B, 7-oxo-amphotericin B and pentaene analogues.

Redesign of polyene macrolide glycosylation: engineered biosynthesis of 19-(O)-perosaminyl-amphoteronolide B.

Most polyene macrolide antibiotics are glycosylated with mycosamine (3,6-dideoxy-3-aminomannose). In the amphotericin B producer, Streptomyces nodosus, mycosamine biosynthesis begins with AmphDIII-catalyzed conversion of GDP-mannose to GDP-4-keto-6-deoxymannose. This is converted to GDP-3-keto-6-deoxymannose, which is transaminated to GDP-mycosamine by the AmphDII protein.

Engineered synthesis of 7-oxo- and 15-deoxy-15-oxo-amphotericins: insights into structure-activity relationships in polyene antibiotics.

Site-directed mutagenesis and gene replacement were used to inactivate two ketoreductase (KR) domains within the amphotericin polyketide synthase in Streptomyces nodosus. The KR12 domain was inactivated in the DeltaamphNM strain, which produces 16-descarboxyl-16-methyl-amphotericins. The resulting mutant produced low levels of the expected 15-deoxy-15-oxo analogs that retained antifungal activity.

Autocatalytic formation of a covalent link between tryptophan 41 and the heme in ascorbate peroxidase.

Electronic spectroscopy, HPLC analyses, and mass spectrometry (MALDI-TOF and MS/MS) have been used to show that a covalent link from the heme to the distal Trp41 can occur on exposure of ascorbate peroxidase (APX) to H2O2 under noncatalytic conditions. Parallel analyses with the W41A variant and with APX reconstituted with deuteroheme clearly indicate that the covalent link does not form in the absence of either Trp41 or the heme vinyl groups. The presence of substrate also precludes formation of the link.

Biosynthesis of amphotericin derivatives lacking exocyclic carboxyl groups.

Amphotericin B is a medically important antifungal antibiotic that is also active against human immunodeficiency virus, Leishmania parasites, and prion diseases. The therapeutic use of amphotericin B is restricted by severe side effects that can be moderated by liposomal formulation or structural alteration. Chemical modification has shown that suppression of charge on the exocyclic carboxyl group of amphotericin B substantially reduces toxicity.

Triol protection with 6-benzoyl-3,4-dihydro-(2H)-pyran.

6-Benzoyl-3,4-dihydro-(2H)-pyran will protect 1,2,3-triols such as glycerol as their corresponding spiro-[5-phenyl-3,6,8-trioxabicyclo[3.2.1]octane-4,2[prime or minute]-tetrahydropyran]s and 1,2,4-triols (less efficiently) as the corresponding trioxabicyclo[3.

Biosynthesis of deoxyamphotericins and deoxyamphoteronolides by engineered strains of Streptomyces nodosus.

Amphotericin B is an antifungal antibiotic produced by Streptomyces nodosus. During biosynthesis of amphotericin, the macrolactone core undergoes three modifications: oxidation of a methyl branch to a carboxyl group, mycosaminylation, and hydroxylation. Gene disruption was undertaken to block two of these modifications.