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Title: Discovery and biosynthesis of cryptic peptide natural products from actinobacteria
Authors: Zhang, Chen
Advisors: Seyedsayamdost, Mohammad R
Contributors: Chemistry Department
Keywords: actinobacteria
natural product
Subjects: Chemistry
Analytical chemistry
Issue Date: 2023
Publisher: Princeton, NJ : Princeton University
Abstract: Natural products have been critical for modern medicine and have illuminated studies in numerous fields, including total synthesis, biochemistry, microbiology, and chemical ecology. The identification of natural product antibiotics bloomed in the 1950s; however, discovery rates have decreased greatly in recent decades. One key bottleneck is that the majority of natural product biosynthetic genes clusters (BGCs) are transcriptionally silent, also referred to as cryptic, under standard laboratory culture conditions, making their products inaccessible with conventional methods. Intense efforts have recently emerged, focusing on unearthing the products of cryptic BGCs to unlock the full biosynthetic potential of talented microbes. This thesis centers on the discovery and biosynthesis of cryptic natural products, with an emphasis on peptides from Actinobacteria, a historically rich source of natural products. Chapter 2 describes a chemical elicitor screening method for the activation of cryptic peptide BGCs, and application of this approach toward the identification of a novel, cyclic depsipeptide, which exhibits antimicrobial activities. Chapter 3 delineates the enzymatic basis of a post-translational hydroxylation in the biosynthesis of a previously isolated lasso peptide natural product. The timing of hydroxylation was determined via in vitro assays and biophysical experiments. Chapters 4 focuses on a unique class of ribosomal peptides modified by cobalamin-dependent radical S-adenosylmethionine (SAM) enzymes. Induction of the corresponding BGC by targeted genetics enabled identification of hyper-methylated amphiphilic peptides. Their function was elucidated based on physical properties and bacterial phenotypic effects. The biosynthesis of the hyper-methylated peptides was examined through in vivo co-expression and in vitro enzyme assays. Finally, Chapter 5 explores cobalamin-dependent radical SAM enzymes in Actinobacteria by bioinformatics and reveals that the peptides described in Chapter 4 are prevalent within the phylum. Together, this thesis implements and leverages modern techniques toward the discovery of new natural products and provides insights into their biosynthetic pathways and physiological functions.
Type of Material: Academic dissertations (Ph.D.)
Language: en
Appears in Collections:Chemistry

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