Elucidating the Sugar Tailoring Steps in the Cytorhodin Biosynthetic Pathway

Anthracycline antitumor cytorhodins X and Y feature a rare 9α-glycoside and 7-dexoy-aglycone. Characterization of the cytorhodin gene cluster from <i>Streptomyces</i> sp. SCSIO 1666 through gene inactivations and metabolite analyses reveals three glycosyltransferases (GTs) involved in the sugar tailoring steps. The duo of CytG1 and CytL effects C-7 glycosylation with l-rhodosamine whereas the iterative GT CytG3 and CytW similarly modifies both C-9 and C-10 positions. CytG2 also acts iteratively by incorporating the second and third sugar moiety into the trisaccharide chains at the C-7 or C-10 position

Discovery of a New Family of Dieckmann Cyclases Essential to Tetramic Acid and Pyridone-Based Natural Products Biosynthesis

Bioinformatic analyses indicate that TrdC, SlgL, LipX₂, KirHI, and FacHI belong to a group of highly homologous proteins involved in biosynthesis of actinomycete-derived tirandamycin B, streptolydigin, α-lipomycin, kirromycin, and factumycin, respectively. However, assignment of their biosynthetic roles has remained elusive. Gene inactivation and complementation, <i>in vitro</i> biochemical assays with synthetic analogues, point mutations, and phylogenetic tree analyses reveal that these proteins represent a new family of Dieckmann cyclases that drive tetramic acid and pyridone scaffold biosynthesis

Cytotoxic Anthracycline Metabolites from a Recombinant <i>Streptomyces</i>

The C7 (C9 or C10)-<i>O</i>-l-rhodosamine-bearing anthracycline antibiotic cytorhodins and their biosynthetic intermediates were recently isolated from <i>Streptomyces</i> sp. SCSIO 1666. Cosmid p17C4 from the <i>Streptomyces lydicus</i> genomic library, which harbors both the biosynthetic genes for l-rhodinose (or 2-deoxy-l-fucose) and its glycosyltransferase (encoded by slgG), was introduced into SCSIO 1666 to yield the recombinant strain <i>Streptomyces</i> sp. SCSIO 1666/17C4. Chemical investigations of this strain’s secondary metabolic potential revealed the production of different anthracyclines featuring C7-<i>O</i>-l-rhodinose (or 2-deoxy-l-fucose) instead of the typically observed l-rhodosamine. Purification of the fermentation broth yielded 12 new anthracycline antibiotics including three new ε-rhodomycinone derivatives, <b>1</b>, <b>4</b>, and <b>8</b>, nine new β-rhodomycinone derivatives, <b>2</b>, <b>3</b>, <b>5</b>–<b>7</b>, and <b>9</b>–<b>12</b>, and three known compounds, l-rhodinose-l-rhodinose-l-rhodinose­rhodomycinone (<b>13</b>), ε-rhodomycinone (<b>14</b>), and γ-rhodomycinone (<b>15</b>). All compounds were characterized on the basis of detailed spectroscopic analyses and comparisons with previously reported data. These compounds exhibited cytotoxicity against a panel of human cancer cell lines. Significantly, compounds <b>4</b> and <b>13</b> displayed pronounced activity against HCT-116 as characterized by IC₅₀ values of 0.3 and 0.2 μM, respectively; these IC₅₀ values are comparable to that of the positive control epirubicin

Δ^11,12 Double Bond Formation in Tirandamycin Biosynthesis is Atypically Catalyzed by TrdE, a Glycoside Hydrolase Family Enzyme

The tirandamycins (TAMs) are a small group of Streptomyces-derived natural products that target bacterial RNA polymerase. Within the TAM biosynthetic cluster, <i>trdE</i> encodes a glycoside hydrolase whose role in TAM biosynthesis has been undefined until now. We report that in vivo <i>trdE</i> inactivation leads to accumulation of pre-tirandamycin, the earliest intermediate released from its mixed polyketide/nonribosomal peptide biosynthetic assembly line. In vitro and site-directed mutagenesis studies showed that TrdE, a putative glycoside hydrolase, catalyzes in a highly atypical fashion the installation of the Δ^11,12 double bond during TAM biosynthesis