-Glucosylation as a Part of Self-Resistance Mechanism in Methymycin/Pikromycin Producing Strain Streptomyces venez
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- 作者：Lishan Zhao ; Noelle J. Beyer ; Svetlana A. Borisova ; and Hung-wen Liu
- 刊名：Biochemistry
- 出版年：2003
- 出版时间：December 23, 2003
- 年：2003
- 卷：42
- 期：50
- 页码：14794 - 14804
- 全文大小：347K
- 年卷期：v.42,no.50(December 23, 2003)
- ISSN：1520-4995
文摘
In our study of the biosynthesis of D-desosamine in Streptomyces venezuelae, we have clonedand sequenced the entire desosamine biosynthetic cluster. The deduced product of one of the genes, desR,in this cluster shows high sequence homology to 
-glucosidases, which catalyze the hydrolysis of theglycosidic linkages, a function not required for the biosynthesis of desosamine. Disruption of the desRgene led to the accumulation of glucosylated methymycin/neomethymycin products, all of which arebiologically inactive. It is thus conceivable that methymycin/neomethymycin may be produced as inertdiglycosides, and the DesR protein is responsible for transforming these antibiotics from their dormant totheir active forms. This hypothesis is supported by the fact that the translated desR gene has a leadersequence characteristic of secretory proteins, allowing it to be transported through the cell membrane andhydrolyze the modified antibiotics extracellularly to activate them. Expression of desR and biochemicalcharacterization of the purified protein confirmed the catalytic function of this enzyme as a -glycosidasecapable of catalyzing the hydrolysis of glucosylated methymycin/neomethymycin produced by S.venezuelae. These results provide strong evidence substantiating glycosylation/deglycosylation as a likelyself-resistance mechanism of S. venezuelae. However, further experiments have suggested that such aglycosylation/deglycosylation is only a secondary self-defense mechanism in S. venezuelae, whereasmodification of 23S rRNA, which is the target site for methymycin and its derivatives, by PikR1 andPikR2 is a primary self-resistance mechanism. Considering that postsynthetic glycosylation is an effectivemeans to control the biological activity of macrolide antibiotics, the availability of macrolide glycosidases,which can be used for the activation of newly formed antibiotics that have been deliberately deactivatedby engineered glycosyltransferases, may be a valuable part of an overall strategy for the development ofnovel antibiotics using the combinatorial biosynthetic approach.
-glucosidases, which catalyze the hydrolysis of theglycosidic linkages, a function not required for the biosynthesis of desosamine. Disruption of the desRgene led to the accumulation of glucosylated methymycin/neomethymycin products, all of which arebiologically inactive. It is thus conceivable that methymycin/neomethymycin may be produced as inertdiglycosides, and the DesR protein is responsible for transforming these antibiotics from their dormant totheir active forms. This hypothesis is supported by the fact that the translated desR gene has a leadersequence characteristic of secretory proteins, allowing it to be transported through the cell membrane andhydrolyze the modified antibiotics extracellularly to activate them. Expression of desR and biochemicalcharacterization of the purified protein confirmed the catalytic function of this enzyme as a -glycosidasecapable of catalyzing the hydrolysis of glucosylated methymycin/neomethymycin produced by S.venezuelae. These results provide strong evidence substantiating glycosylation/deglycosylation as a likelyself-resistance mechanism of S. venezuelae. However, further experiments have suggested that such aglycosylation/deglycosylation is only a secondary self-defense mechanism in S. venezuelae, whereasmodification of 23S rRNA, which is the target site for methymycin and its derivatives, by PikR1 andPikR2 is a primary self-resistance mechanism. Considering that postsynthetic glycosylation is an effectivemeans to control the biological activity of macrolide antibiotics, the availability of macrolide glycosidases,which can be used for the activation of newly formed antibiotics that have been deliberately deactivatedby engineered glycosyltransferases, may be a valuable part of an overall strategy for the development ofnovel antibiotics using the combinatorial biosynthetic approach.