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Related Concept Videos

Radical Reactivity: Overview01:11

Radical Reactivity: Overview

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Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
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Radical Formation: Overview01:03

Radical Formation: Overview

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A bond can be broken either by heterolytic bond cleavage to form ions or homolytic bond cleavage to yield radicals. A fishhook arrow is used to represent the motion of a single electron in homolytic bond cleavage. There are two main sources from which radicals can be formed:
Radicals from spin-paired molecules:
Radicals can be obtained from spin-paired molecules either by homolysis or electron transfer. While two radicals are formed in the former, an electron is added in the...
2.1K
Radical Reactivity: Steric Effects01:10

Radical Reactivity: Steric Effects

1.9K
The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic...
1.9K
Radical Reactivity: Nucleophilic Radicals01:16

Radical Reactivity: Nucleophilic Radicals

2.1K
Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For...
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Radical Formation: Addition00:47

Radical Formation: Addition

1.7K
Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
Similar to charge conservation in chemical reactions, spin conservation is implicit for radical reactions. Accordingly, the product formed must possess an...
1.7K
Radical Reactivity: Electrophilic Radicals01:02

Radical Reactivity: Electrophilic Radicals

1.9K
Radicals adjacent to electron‐withdrawing groups are called electrophilic radicals. These radicals readily react with nucleophilic alkenes. For example, the malonate radical, in which the radical center is flanked by two electron‐withdrawing groups, reacts readily with butyl vinyl ether, which consists of an electron‐donating oxygen substituent. The reaction between electrophilic malonate radical and nucleophilic vinyl ether is favored because the radical has a...
1.9K

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Structural, Biochemical, and Bioinformatic Basis for Identifying Radical SAM Cyclopropyl Synthases.

Yi Lien1, Jake C Lachowicz2, Aigera Mendauletova1

  • 1Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80210, United States.

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|January 31, 2024
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Summary
This summary is machine-generated.

Researchers identified novel cyclopropyl (CP) synthases, crucial for forming cyclopropylglycine (CPG) in ribosomally synthesized and post-translationally modified peptides (RiPPs). A crystal structure revealed a unique tyrosyl ligation essential for enzyme activity.

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Enzymology

Background:

  • Radical S-adenosyl-l-methionine (RS) enzymes, particularly the RS-SPASM subfamily, are vital for modifying peptides.
  • Cyclopropane scaffolds are important in pharmaceutical development, necessitating a deeper understanding of their synthesis.

Purpose of the Study:

  • To define the family of cyclopropyl (CP) synthases.
  • To characterize a novel CP synthase, TigE, and its associated RiPP pathway.
  • To elucidate the structural and mechanistic basis of CP synthase activity.

Main Methods:

  • Bioinformatic expansion of CP synthases using RadicalSAM.org.
  • Identification and characterization of the TigB precursor peptide and TigE enzyme.
  • Liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) analyses.
  • X-ray crystallography of TigE.

Main Results:

  • A novel RiPP pathway involving the TigB peptide with a repeating TIGSVS motif was identified.
  • TigE was shown to catalyze the formation of methyl-cyclopropylglycine (methyl-CPG) from isoleucine within TigB.
  • The crystal structure of TigE revealed a unique glycine-tyrosine-tryptophan motif enabling tyrosyl ligation to the [4Fe-4S] cluster, essential for activity.

Conclusions:

  • The study defines the CP synthase family and characterizes a novel member, TigE.
  • A unique mechanism involving tyrosyl ligation to an auxiliary cluster is crucial for CP synthase function.
  • These findings provide insights into the biosynthesis of cyclopropane-containing peptides.