Ketopremithramycins and Ketomithramycins, Four New Aureolic Acid-Type Compounds Obtained upon Inactivation of Two Genes Involved in the Biosynthesis of the Deoxysugar Moieties of the Antitumor Drug Mi

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• 作者：Lily L. Remsing ; Jose Garcia-Bernardo ; Ana Gonzalez ; Eva Kü ; nzel ; Uwe Rix ; Alfredo F. Brañ ; a ; Daniel W. Bearden ; Carmen Mé ; ndez ; Jose A. Salas ; and Jü ; rgen Rohr
• 刊名：Journal of the American Chemical Society
• 出版年：2002
• 出版时间：February 27, 2002
• 年：2002
• 卷：124
• 期：8
• 页码：1606 - 1614
• 全文大小：129K
• 年卷期：v.124,no.8(February 27, 2002)
• ISSN：1520-5126

文摘

Mithramycin is an aureolic acid-type antimicrobial and antitumor agent produced by Streptomycesargillaceus. Modifying post-polyketide synthase (PKS) tailoring enzymes involved in the production ofmithramycin is an effective way of gaining further information regarding the late steps of its biosyntheticpathway. In addition, new "unnatural" natural products of the aureolic acid-type class are likely to beproduced. The role of two such post-PKS tailoring enzymes, encoded by mtmC and mtmTIII, wasinvestigated, and four novel aureolic acid class drugs, two premithramycin-type molecules and twomithramycin derivatives, were isolated from mutant strains constructed by insertional gene inactivation ofeither of these two genes. From data bank comparisons, the corresponding proteins MtmC and MtmTIIIwere believed to act as a C-methyltransferase involved in the production of the D-mycarose (sugar E) ofmithramycin and as a ketoreductase seemingly involved in the biosynthesis of the mithramycin aglycon,respectively. However, gene inactivation and analysis of the accumulated products revealed that both genesencode enzymes participating in the biosynthesis of the D-mycarose building block. Furthermore, theinactivation of MtmC seems to affect the ketoreductase responsible for 4-ketoreduction of sugar C, aD-olivose. Instead of obtaining premithramycin and mithramycin derivatives with a modified E-sugar uponinactivation of mtmC, compounds were obtained that completely lack the E-sugar moiety and that possessan unexpected 4-ketosugar moiety instead of the D-olivose at the beginning of the lower deoxysaccharidechain. The inactivation of mtmTIII led to the accumulation of 4E-ketomithramycin, showing that thisketoreductase is responsible for the 4-ketoreduction of the D-mycarose moiety. The new compounds ofthe mutant strains, 4A-ketopremithramycin A2, 4A-keto-9-demethylpremithramycin A2, 4C-keto-demycarosylmithramycin, and 4E-ketomithramycin, indicate surprising substrate flexibility of post-PKS enzymesof the mithramycin biosynthetic pathway. Although the glycosyltransferase responsible for the attachmentof D-mycarose cannot transfer the unmethylated sugar to the existing lower disaccharide chain, it can transferthe 4-ketoform of sugar E. In addition, the glycosyltransferase MtmGIV, which is responsible for the linkageof sugar C, is also able to transfer an activated 4-ketosugar. The oxygenase MtmOIV, normally responsiblefor the oxidative cleavage of the tetracyclic premithramycin B into the tricyclic immediate precursor ofmithramycin, can act on a substrate analogue with a modified or even incomplete trisaccharide chain. Thesame is true for glycosyltransferases MtmGI and MtmGII, both of which partake in the formation andattachment of the A-B disaccharide in mithramycin.