Studies on the Biosynthesis and Isolation of the Biosynthetic Gene Cluster for the Salinosporamides of the Marine Bacterium Salinospora tropica

Persistent Link:
http://hdl.handle.net/10150/194242
Title:
Studies on the Biosynthesis and Isolation of the Biosynthetic Gene Cluster for the Salinosporamides of the Marine Bacterium Salinospora tropica
Author:
Beer, Laura Lynn
Issue Date:
2006
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Salinosporamide A is a potent inhibitor of the 20S proteasome and has recently entered phase I human clinical trials for the treatment of multiple myeloma. This novel marine natural product is produced by the recently described marine bacterium Salinispora tropica. Salinosporamide A contains an unusual fused gamma-lactam-beta-lactone ring structure that is uniquely functionalized. Its biosynthesis has been examined through feeding experiments with 13C-labeled precursors and a biosynthetic gene cluster has been isolated. Feeding experiments indicate that salinosporamide A is assembled from three distinct precursor molecules, namely acetate, a non-proteinogenic amino acid arising from a shunt in the shikimic acid pathway and a chlorinated tetrose molecule. Analysis of the biosynthetic gene cluster revealed that a mixed polyketide synthase (PKS) / nonribosomal peptide synthetase (NRPS) pathway is present. Three ORFs encode a large multifunctional type I PKS with a C-terminal NRPS C-domain (salA) an NRPS (salB) and a stand-alone type I KS domain (salC). Genes are also present for biosynthesis of the unusual amino acid including genes encoding a deoxy-arabino-heptulosonate-7-phosphate (DAHP) synthase (salU), a cytochrome P450 oxygenase (salD) and a potential prephenate dehydratase (salX). An unprecedented pathway for biosynthesis of chlorobutyrate is present that utilizes 5'chloro-5'-deoxyadenosine synthase (salL) in a pathway analogous to the fluorinase from Streptomyces cattleya. The cyclization and offloading may be facilitated by salO and salF that encode a cyclase and a thioesterase respectivy. A gene encoding a proteasome 20S -subunit (salJ) may be involved in resistance and genes encoding transcriptional regulatory proteins in addition to genes with no known function are also present in the cluster. Based on results from feeding experiments and the putative gene cluster, a biosynthetic scheme for salinosporamide A and some of the lesser produced salinosporamide analogs is proposed.
Type:
text; Electronic Dissertation
Degree Name:
PhD
Degree Level:
doctoral
Degree Program:
Pharmacology & Toxicology; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Moore, Bradley S
Committee Chair:
Moore, Bradley S

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleStudies on the Biosynthesis and Isolation of the Biosynthetic Gene Cluster for the Salinosporamides of the Marine Bacterium Salinospora tropicaen_US
dc.creatorBeer, Laura Lynnen_US
dc.contributor.authorBeer, Laura Lynnen_US
dc.date.issued2006en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractSalinosporamide A is a potent inhibitor of the 20S proteasome and has recently entered phase I human clinical trials for the treatment of multiple myeloma. This novel marine natural product is produced by the recently described marine bacterium Salinispora tropica. Salinosporamide A contains an unusual fused gamma-lactam-beta-lactone ring structure that is uniquely functionalized. Its biosynthesis has been examined through feeding experiments with 13C-labeled precursors and a biosynthetic gene cluster has been isolated. Feeding experiments indicate that salinosporamide A is assembled from three distinct precursor molecules, namely acetate, a non-proteinogenic amino acid arising from a shunt in the shikimic acid pathway and a chlorinated tetrose molecule. Analysis of the biosynthetic gene cluster revealed that a mixed polyketide synthase (PKS) / nonribosomal peptide synthetase (NRPS) pathway is present. Three ORFs encode a large multifunctional type I PKS with a C-terminal NRPS C-domain (salA) an NRPS (salB) and a stand-alone type I KS domain (salC). Genes are also present for biosynthesis of the unusual amino acid including genes encoding a deoxy-arabino-heptulosonate-7-phosphate (DAHP) synthase (salU), a cytochrome P450 oxygenase (salD) and a potential prephenate dehydratase (salX). An unprecedented pathway for biosynthesis of chlorobutyrate is present that utilizes 5'chloro-5'-deoxyadenosine synthase (salL) in a pathway analogous to the fluorinase from Streptomyces cattleya. The cyclization and offloading may be facilitated by salO and salF that encode a cyclase and a thioesterase respectivy. A gene encoding a proteasome 20S -subunit (salJ) may be involved in resistance and genes encoding transcriptional regulatory proteins in addition to genes with no known function are also present in the cluster. Based on results from feeding experiments and the putative gene cluster, a biosynthetic scheme for salinosporamide A and some of the lesser produced salinosporamide analogs is proposed.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplinePharmacology & Toxicologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorMoore, Bradley Sen_US
dc.contributor.chairMoore, Bradley Sen_US
dc.contributor.committeememberHurley, Laurenceen_US
dc.contributor.committeememberJacobson, Elaineen_US
dc.contributor.committeememberCordes, Matthewen_US
dc.identifier.proquest1967en_US
dc.identifier.oclc659746544en_US
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