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ATP Synthase: Mechanism01:48

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SN2 substitutions and E2 eliminations of alkyl halides proceed via a concerted pathway. While the nucleophile attacks the alpha carbon in SN2 reactions, it functions as a strong base and abstracts a beta hydrogen in the E2 mechanism. The rate-limiting transition state in E2 elimination reactions is characterized by partially broken carbon–hydrogen and carbon–halogen bonds and a partially formed pi bond between the alpha and beta carbons. The beta hydrogen and halide are eliminated...
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Structural insights into thebaine synthase 2 catalysis.

Chun-Chi Chen1, Jing Xue1, Wei Peng2

  • 1State Key Laboratory of Biocatalysis and Enzyme Engineering, Hubei Collaborative Innovation Center for Green Transformation of Bio-Resources, Hubei Key Laboratory of Industrial Biotechnology, School of Life Sciences, Hubei University, Wuhan, 430062, PR China.

Biochemical and Biophysical Research Communications
|July 25, 2020
PubMed
Summary

Thebaine synthase 2 (THS2) enzyme

Keywords:
AnalgesicCrystal structureMorphine biosynthesisThebaine synthase

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Area of Science:

  • Biochemistry
  • Enzymology
  • Structural Biology

Background:

  • Papaver somniferum is a key source of opiate alkaloids.
  • Thebaine biosynthesis involves complex enzymatic pathways.
  • Understanding the final enzymatic step is crucial for metabolic engineering.

Purpose of the Study:

  • Elucidate the catalytic mechanism of Thebaine synthase 2 (THS2).
  • Determine the crystal structure of THS2 and its complex with thebaine.
  • Investigate the rate-determining step in thebaine biosynthesis.

Main Methods:

  • X-ray crystallography to determine enzyme structure.
  • Molecular docking to model substrate-enzyme interactions.
  • Quantum Mechanics/Molecular Mechanics (QM/MM) studies for mechanistic insights.

Main Results:

  • Crystal structures of THS2 and THS2-thebaine complex revealed substrate-binding pocket interactions.
  • Proposed a catalytic mechanism involving proton abstraction by T105 and SN2' displacement.
  • Identified the SN2' reaction as the rate-determining step with an energy barrier of 18.8 kcal/mol.

Conclusions:

  • The study provides a detailed mechanistic understanding of THS2 in thebaine biosynthesis.
  • Findings are critical for guiding enzyme engineering strategies.
  • Potential to enhance opiate alkaloid production through metabolic engineering.