| 說明 |
246 p |
| 附註 |
Source: Dissertation Abstracts International, Volume: 70-05, Section: B, page: 2898 |
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Adviser: Shiou-Chuan Tsai |
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Thesis (Ph.D.)--University of California, Irvine, 2009 |
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Polyketides are a class of natural products with diverse chemical structures and important biological activities. The biosynthetic enzymes, acyl-CoA precursors, and chemical reactions that biosynthesize polyketides are similar to those used in fatty acid biosynthesis. However, the biosynthetic logic of fatty acid synthase (FAS) versus polyketide synthase (PKS) affords vastly different end products: while FAS yields fully-reduced, aliphatic products, PKS produces a diverse array of molecular scaffolds that are often highly derivatized chemically. In comparison to the simple structure of fatty acids, a central question underlying research into polyketide biosynthesis is how PKS can precisely control chain elongation, functional-group modification, cyclization, and tailoring reactions to accomplish such product diversity |
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The objective of this dissertation is to understand: (1) the regiospecific cyclization of an unreduced polyketide chain by the Type II PKS aromatase/cyclase (ARO/CYC) for aromatic polyketide biosynthesis, and (2) the substrate specificity of the trans-acting enoyl reductase LovC (iterative Type I PKS) for the biosynthesis of the cholesterol-lowering drug lovastatin |
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The crystal structures and functional analyses of three PKS ARO/CYCs are reported. The ARO/CYC possesses a helix-grip fold characterized by the presence of a large, solvent-accessible interior pocket. Co-crystal structures demonstrate that the interior pocket of ARO/CYC can bind polyketides, while docking simulations of putative biosynthetic intermediates illustrates how the ARO/CYC pocket may influence cyclization specificity and catalyze intramolecular aldol condensation. Mutations to pocket residues were assayed by reconstituting polyketide biosynthesis, demonstrating that the interior pocket of ARO/CYC is critical for polyketide cyclization |
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The crystal structure of LovC shows that it is a unique monomeric medium-chain dehydrogenase/reductase (MDR) family member. We developed an in vitro activity assay to prove that LovC is enzymatically active as a standalone protein. Corresponding to the observed substrate specificity of LovC in vivo, the synthesis and testing of surrogate substrates showed that LovC does not reduce the shorter-chain diketide or triketide compounds, but does reduce the alpha-beta unsaturated tetraketide mimic, ( E)-2-octenoyl-N-acetylcysteamine. LovC structural analysis, activity assays, and substrate docking suggest that the LovC active site can effectively discriminate between intermediates to selectively reduce three out of six possible intermediates during lovastatin biosynthesis |
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School code: 0030 |
| Host Item |
Dissertation Abstracts International 70-05B
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| 主題 |
Biology, Molecular
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Biology, Microbiology
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Chemistry, Biochemistry
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0307
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0410
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0487
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| Alt Author |
University of California, Irvine. Biological Sciences - Ph.D
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