Structural and functional Studies of angucycline tailoring enzymes

Polyketides are a diverse group of natural products produced in many bacteria, fungi and plants. These metabolites have diverse biological activities and several members of this group are in clinical use as antibiotics, anticancer agents, antifungals and immunosuppressants. The different polyketides are produced by polyketide synthases, which catalyze the condensation of extender units into various polyketide scaffolds. After the biosynthesis of the polyketide backbone, more versatility is created to the molecule by tailoring enzymes catalyzing for instance hydroxylations, methylations and glycosylations. Flavoprotein monooxygenases (FPMO) and short-chain alcohol dehydrogenases/reductases (SDR) are two enzyme families that catalyze unusual tailoring reactions in the biosynthesis of natural products. In the experimental section, functions of homologous FPMO and SDR tailoring enzymes from five different angucycline pathways were studied in vitro. The results revealed how different angucyclinones are produced from a common intermediate and that FPMO JadH and SDR LanV are responsible for the divergence of jadomycins and landomycins, respectively, from other angucyclines. Structural studies of these tailoring enzymes revealed differences between homologous enzymes and enabled the use of structure-based protein engineering. Mutagenesis experiments gave important information about the enzymes behind the evolution of distinct angucycline metabolites. These experiments revealed a correlation between the substrate inhibition and bi-functionality in JadH homologue PgaE. In the case of LanV, analysis of mutagenesis results revealed that the difference between the stereospecificities of LanV and its homologues CabV and UrdMred is unexpectedly related to the conformation of the substrate rather than to the structure of the enzyme. Altogether, the results presented here have improved our knowledge about different steps of angucycline biosynthesis and the reaction mechanisms used by the tailoring enzymes behind these steps. This information can hopefully be used to modify these enzymes to produce novel metabolites, which have new biological targets or possess novel modes-of-action. The understanding of these unusual enzyme mechanisms is also interesting to enzymologists outside the field of natural product research.

Occupation de Constantinople par les Alliés, à bord d'un navire de guerre anglais, la femme du fils aîné du sultan : [photographie de presse] / [Agence Rol]

Référence bibliographique : Rol, 58870

Letter written by Mahlon Taylor to Samuel Clarke commenting on US troops during Fort George occupation, July 26, 1813

Fort George, situated on the west side of the Niagara River in Niagara-on-the-Lake, served as the headquarters for the Centre Division of the British Army during the War of 1812. On May 25, 1813, the Americans launched an artillery attack on the Fort, destroying most of the buildings. Two days later, the Americans invaded the Town of Niagara and occupied Fort George. They remained in the Fort for almost seven months, but suffered defeats at the Battle of Stoney Creek and Beaver Dams. Only a small number of militia remained stationed at the Fort. Fearing an attack by the British, the Americans retreated back across the Niagara River in December, 1813. The Fort remained in British possession for the rest of the War.

Letter written by Mahlon Taylor to Samuel Clarke commenting on US troops during Fort George occupation - July 26, 1813

A letter written by Mahlon Taylor to his uncle, Samuel Clarke, dated at Marcellus [New York], July 26, 1813. Mahlon Taylor writes that he believes the mail he has sent out is not making it past Princeton, as he has not had a reply to any of his sent correspondence. He also writes that he has heard there are 3500 men at Fort George, 1000 are unfit for duty, and that there is skirmishing daily. He comments that the general opinion is that the troops will withdraw from Canada entirely. The letter is signed Mahlon C Taylor and is addressed to Mr. Samuel Clarke, no. 227 South Front Street, Philadelphia.