12 research outputs found
The Rieske Oxygenase SnoT Catalyzes 2''-Hydroxylation of L-Rhodosamine in Nogalamycin Biosynthesis
Nogalamycin is an anthracycline anti-cancer agent that intercalates into the DNA double helix. The binding is facilitated by two carbohydrate units, L-nogalose and L-nogalamine, that interact with the minor and major grooves of DNA, respectively. However, recent investigations have shown that nogalamycin biosynthesis proceeds through the attachment of l-rhodosamine (2â˛â˛-deoxy-4â˛â˛-epi-L-nogalamine) to the aglycone. Herein, we demonstrate that the Rieske enzyme SnoT catalyzes 2â˛â˛-hydroxylation of L-rhodosamine as an initial post-glycosylation step. Furthermore, we establish that the reaction order continues with 2â5â˛â˛ carbocyclization and 4â˛â˛ epimerization by the non-heme iron and 2-oxoglutarate-dependent enzymes SnoK and SnoN, respectively. These late-stage tailoring steps are important for the bioactivity of nogalamycin due to involvement of the 2â˛â˛- and 4â˛â˛-hydroxy groups of á´¸-nogalamine in hydrogen bonding interactions with DNA.</p
Asymptomatic Right Atrial Thrombosis After Acute Lymphoblastic Leukemia Treatment
Right atrial thrombosis is a rare, but potentially serious complication of acute lymphoblastic leukemia treatment. We conducted a retrospective multicenter study to assess the incidence, treatment, and outcome of asymptomatic right atrial thrombosis detected at routine echocardiography of children after acute lymphoblastic leukemia treatment in the Nordic and Baltic countries. Eleven (2.7%, 95% confidence interval, 1.4-4.9) of 406 patients had asymptomatic right atrial thrombosis, ranging from 10 to 25 mm at detection. Three patients were treated with anticoagulation. None of the thromboses affected cardiac function, and they showed neither sign of progress nor spontaneous or treatment-related regress at follow-up.Peer reviewe
The role of the maleimide ring system on the structure-activity relationship of showdomycin
Showdomycin produced by Streptomyces showdoensis ATCC 15227 is a C-nucleoside microbial natural product with antimicrobial and cytotoxic properties. The unique feature of showdomycin in comparison to other nucleosides is its maleimide base moiety, which has the distinct ability to alkylate nucleophilic thiol groups by a Michael addition reaction. In order to understand structure-activity relationships of showdomycin, we synthesized a series of derivatives with modifications in the maleimide ring at the site of alkylation to moderate its reactivity. The showdomycin congeners were designed to retain the planarity of the base ring system to allow Watson-Crick base pairing and preserve the nucleosidic character of the compounds. Consequently, we synthesized triphosphates of showdomycin derivatives and tested their activity against RNA polymerases. Bromo, methylthio, and ethylthio derivatives of showdomycin were incorporated into RNA by bacterial and mitochondrial RNA polymerases and somewhat less efficiently by the eukaryotic RNA polymerase II. Showdomycin derivatives acted as uridine mimics and delayed further extension of the RNA chain by multi-subunit, but not mitochondrial RNA polymerases. Bioactivity profiling indicated that the mechanism of action of ethylthioshowdomycin was altered, with approximately 4-fold reduction in both cytotoxicity against human embryonic kidney cells and antibacterial activity against Escherichia coli. In addition, the ethylthio derivative was not inactivated by medium components or influenced by addition of uridine in contrast to showdomycin. The results explain how both the maleimide ring and the nucleoside nature contribute to the bioactivity of showdomycin and demonstrates for the first time that the two activities can be separated.</p
Discovery of the Showdomycin Gene Cluster from Streptomyces showdoensis ATCC 15227 Yields Insight into the Biosynthetic Logic of C-Nucleoside Antibiotics
Engineering Anthracycline Biosynthesis toward Angucyclines
The biosynthesis pathways of two anthracyclines, nogalamycin and aclacinomycin, were directed toward angucyclines by using an angucycline-specific cyclase, pgaF, isolated from a silent antibiotic biosynthesis gene cluster. Addition of pgaF to a gene cassette that harbored the early biosynthesis genes of nogalamycin resulted in the production of two known angucyclinone metabolites, rabelomycin and its precursor, UWM6. Substrate flexibility of pgaF was demonstrated by replacement of the nogalamycin minimal polyketide synthase genes in the gene cassette with the equivalent aclacinomycin genes together with aknE2 and aknF, which specify the unusual propionate starter unit in aclacinomycin biosynthesis. This modification led to the production of a novel angucyclinone, MM2002, in which the expected ethyl side chain was incorporated into the fourth ring
Randomized controlled and double-blinded study of Caphosol versus saline oral rinses in pediatric patients with cancer
Randomized controlled and doubleâblinded study of Caphosol versus saline oral rinses in pediatric patients with cancer
Asymptomatic Right Atrial Thrombosis After Acute Lymphoblastic Leukemia Treatment
Right atrial thrombosis is a rare, but potentially serious complication of acute lymphoblastic leukemia treatment. We conducted a retrospective multicenter study to assess the incidence, treatment, and outcome of asymptomatic right atrial thrombosis detected at routine echocardiography of children after acute lymphoblastic leukemia treatment in the Nordic and Baltic countries. Eleven (2.7%, 95% confidence interval, 1.4-4.9) of 406 patients had asymptomatic right atrial thrombosis, ranging from 10 to 25 mm at detection. Three patients were treated with anticoagulation. None of the thromboses affected cardiac function, and they showed neither sign of progress nor spontaneous or treatment-related regress at follow-up.Peer reviewe
Discovery of the Showdomycin Gene Cluster from <i>Streptomyces showdoensis</i> ATCC 15227 Yields Insight into the Biosynthetic Logic of CâNucleoside Antibiotics
Nucleoside
antibiotics are a large class of pharmaceutically relevant
chemical entities, which exhibit a broad spectrum of biological activities.
Most nucleosides belong to the canonical N-nucleoside family, where
the heterocyclic unit is connected to the carbohydrate through a carbonânitrogen
bond. However, atypical C-nucleosides were isolated from <i>Streptomyces</i> bacteria over 50 years ago, but the molecular basis for formation
of these metabolites has been unknown. Here, we have sequenced the
genome of <i>S. showdoensis</i> ATCC 15227 and identified
the gene cluster responsible for showdomycin production. Key to the
detection was the presence of <i>sdmA</i>, encoding an enzyme
of the pseudouridine monophosphate glycosidase family, which could
catalyze formation of the C-glycosidic bond. Sequence analysis revealed
an unusual combination of biosynthetic genes, while inactivation and
subsequent complementation of <i>sdmA</i> confirmed the
involvement of the locus in showdomycin formation. The study provides
the first steps toward generation of novel C-nucleosides by pathway
engineering