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Visualization of Bacterial Resistance using Fluorescent Antibiotic Probes

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Michael-type cyclizations in lantibiotic biosynthesis are reversible.

Xiao Yang¹, Wilfred A van der Donk¹

¹Howard Hughes Medical Institute and Roger Adams Laboratory, Department of Chemistry, University of Illinois at Urbana-Champaign, 600 South Mathews Avenue, Urbana, Illinois 61801, United States.

ACS Chemical Biology

|February 28, 2015

Summary

The study demonstrates that lanthipeptide thioether ring formation is reversible, with enzymes like NisC and HalM2 capable of opening these structures. A conserved histidine residue likely facilitates this ring opening and closing mechanism.

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Published on: February 7, 2019

Area of Science:

Biochemistry
Molecular Biology
Structural Biology

Background:

Lanthipeptides are ribosomally synthesized and post-translationally modified peptides (RiPPs) characterized by multiple thioether cross-links.
The formation of these thioether bridges involves dehydration and conjugate addition reactions.
Previous hypotheses suggested thermodynamic control over lanthipeptide ring topology, implying reversible cyclization, but this remained unproven.

Purpose of the Study:

To investigate the reversibility of thioether ring formation in lanthipeptides.
To determine if lanthipeptide cyclases can open pre-formed thioether structures.
To elucidate the role of conserved residues in the cyclization/decyclization mechanism.

Main Methods:

Enzymatic assays using class I lanthipeptide cyclase NisC and class II lanthipeptide synthetase HalM2.
Analysis of thioether ring formation and opening reactions.
Site-directed mutagenesis to probe the function of conserved histidine residues.

Main Results:

Demonstrated that the conjugate addition reactions catalyzed by NisC and HalM2 are reversible.
Showed that these enzymes can effectively open all thioether rings in their respective lanthipeptide products.
Identified a conserved histidine residue in lanthipeptide cyclases as a key catalytic residue involved in both ring formation and opening.

Conclusions:

The formation and stability of lanthipeptide thioether rings are not irreversible.
Lanthipeptide cyclases possess the ability to catalyze both the formation and the precise reversal of thioether cross-links.
A conserved histidine residue plays a critical role in the acid-base catalysis required for the reversible Michael-type cyclization reactions in lanthipeptide biosynthesis.