Date of Award


Document Type


Degree Name



Chemistry and Biochemistry

First Advisor

John A. Latham

Second Advisor

Scott Nichols

Third Advisor

Martin Margittai

Fourth Advisor

Michelle K. Knowles


Bioinformatics, Radical-S-adenosylmethionine enzyme, Ribosomally synthesized and posttranslationally modified peptide, Sequence similarity network, TIG biosynthesis


Ribosomally synthesized and post-translationally modified peptides (RiPPs) are a large class of natural products with significant human health implications. RiPPs are synthesized from a genetically encoded precursor peptide that undergoes significant modifications by maturing enzymes, or maturases. Recently, radical-S-adenosylmethionine (rSAM) enzymes have emerged as an important family of RiPP maturases. rSAM enzymes have been shown to install ether, thioether, and carbon-carbon bonds on the precursor peptide. These modifications usually define the backbone structure of the mature RiPP. This thesis describes the characterization of a novel RiPP modification catalyzed by the radical S-adenosylmethionine enzyme TigE. TigE belongs to the TIG biosynthetic gene cluster (BGC), which is encoded by tigABCDEF, found in the bacterium Paramaledivibacter caminithermalis. The TIG precursor peptide, TigB, is comprised of a repeating TIGSVSG motif. Using a variety of chromatography, mass spectrometry, isotopic labeling, and NMR spectroscopy techniques, we show that TigE catalyzes the formation of C-C bond between the γ-carbons on TigB isoleucine residues (Ile), forming a methyl-cyclopropyl glycine (mCPG). Using crystallography and site-directed mutagenesis, we also revealed that the TigE residue Tyr339 is critical for both the coordination of iron-sulfur clusters and chemistry and could be used as a biomarker for the discovery of other cyclopropyl synthases. This novel RiPP modification provided a reaction scope of radical S-adenosylmethionine enzymes.

Publication Statement

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Received from ProQuest

Rights holder

Yi Lien

File size

65 pgs

File format





Biochemistry, Chemistry

Available for download on Thursday, September 26, 2024