1997 Fiscal Year Final Research Report Summary
Functional analysis of genes for polyketide synthase
| Project/Area Number |
08680635
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Bioorganic chemistry
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| Research Institution | School of Pharmaceutical Sciences, Kitasato University |
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Principal Investigator |
IKEDA Haruo Kitasato University, Pharmaceutical Sciences, Associate Professor, 薬学部, 助教授 (90159632)
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| Project Period (FY) |
1996 – 1997
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| Keywords | Avermectin / Biosynthesis / Biosynthetic genes / Polyketide / Polyketide synthase |
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| Research Abstract |
Avermectins are a series of 16-membered macrocyclic lactones produced by Streptomyces avermitilis. They are pentacyclic polyketide-derived compounds linked to a disaccharide of the methylated deoxysugar. Within the 90 kbp gene cluster for avermectin biosynthesis, the central 65 kbp segment was found to be required for aglycone biosynthesis (it is performed by catalytic reactions of polyketide synthase ; PKS) by phenotypic analysis of strains containing deletion or insertion mutations in this region. The avermectin PKS genes are organized into two convergently transcribed clusters. The biosynthesis of avermectin aglycone requires twelve acyl condensations of short-chain fatty acids. To elucidate the biosynthetic mechanism of the formation of the aglycone moiety, we determined DNA sequence of the half of this region (aveAI).A sequence analysis of this region within the gene cluster for avermectin biosynthesis indicated that the segment encodes two ORFs, the avermectin polyketide synthases (PKS). From the results of sequencing analysis, a feature of this region, aveAI,is that it encodes two large multifunctional polypeptides containing domains possessing putative fatty acid synthase (FAS)-like activities. PKS-1 and PKS-2 are composed with two and four repeats of FAS-like functions, respectively. The DNA encoding each repeated unit is called a module or synthase unit (SU) which catalyzes a round of acyl condensation and modification of beta-carbon. Although almost each domain in SUs were similar to each other, acyltransferase domains (AT) cluster into two group. Avermectin is composed of with malonate and methylmalonate building blocks. One of the groups contains only the proposed malonate loading functions and the other contains methylmalonate loading function.
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