Stereochemical control in lanthipeptide biosynthesis

Sarksian, Raymond

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https://hdl.handle.net/2142/120504 Copy

Description

Title

Stereochemical control in lanthipeptide biosynthesis

Author(s)

Sarksian, Raymond

Issue Date

2023-04-12

Director of Research (if dissertation) or Advisor (if thesis)

van der Donk, Wilfred A

Doctoral Committee Chair(s)

van der Donk, Wilfred A

Committee Member(s)

• Hergenrother, Paul J
• Chan, Jeff
• Olshansky, Lisa

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• natural products
• lanthipeptide
• stereochemistry
• enzymatic reactions

Abstract

Lanthipeptides are polycyclic natural products that contain lanthionine (Lan) and/or methyllanthionine (MeLan) cross-links. These thioether macrocycles in lanthipeptides bestow upon these molecules their unique bioactivities and provide proteolytic stability. Despite the complex structure of lanthipeptides, these natural products are derived from simple ribosomally synthesized linear precursor peptides that contain all L-amino acids. The linear precursor peptides are extensively post-translationally modified through dehydration and cyclization reactions to generate stereochemically defined (Me)Lan residues. As with other natural products, the complex stereochemistry of lanthipeptides, particularly the stereochemical configuration of (Me)Lan residues, is critical for their biological activities. The research studies described herein focus on investigating lanthipeptide stereochemistry and how stereochemistry is controlled during the biosynthesis of lanthipeptides. In chapter 2, the morphogenetic lanthipeptide SapT was discovered to be the first lanthipeptide to contain D-allo-L-MeLan macrocycles. Critical to the discovery of the D-allo-L-MeLan diastereomer in SapT was developing synthetic and analytical methods to unambiguously determine MeLan stereochemistry. The unusual product stereochemistry in SapT prompted mechanistic studies in chapter 3 to determine how D-allo-L-MeLan cross-links were formed. Through structural characterization of a model biosynthetic intermediate, it was determined that SapT biosynthesis proceeds through (E)- rather than (Z)-dehydrobutyrine (Dhb) intermediates that have been observed previously for all characterized lanthipeptides. The glutamyl lyase (GL) in SapT biosynthesis was thus shown to catalyze stereoselective syn-elimination. In chapter 4, additional syn-GLs were bioinformatically identified in lanthipeptide biosynthetic gene clusters and one representative gene cluster termed coi was experimentally investigated. The coi gene cluster was determined to generate a polycyclic lanthipeptide termed mCoiA1 that contained three MeLan diastereomers, each at different locations within the peptide. One of the MeLan residues in mCoiA1 was determined to be a D-allo-L-MeLan residue. Therefore, the studies outlined in chapter 4 illustrated that D-allo-L-MeLan macrocycles are not limited to SapT, but are rather common in lanthipeptides and can be predicted based on the amino acid sequence of the GL. Finally, in chapter 5 experimental studies were aimed towards elucidating how lanthipeptide cyclases control and alter Lan product stereochemistry. The studies described in this thesis illustrate how stereochemistry is tightly regulated enzymatically in nature to produce stereochemically complex peptidic natural products and provide direction towards future investigations into lanthipeptides.

Graduation Semester

2023-05

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Raymond Sarksian

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