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Visualizing molecular juggling within a B12-dependent methyltransferase complex.

Yan Kung1, Nozomi Ando, Tzanko I Doukov

  • 1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

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|March 16, 2012
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Summary

This study reveals the complete structure of a large enzyme complex essential for vitamin B12-dependent methyl transfer. It visualizes the cofactor

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Enzymology

Background:

  • Vitamin B12 derivatives are crucial for methyl group transfer in vital biological processes.
  • Existing structural data only covered fragments of the large enzyme complexes involved.

Purpose of the Study:

  • To present the complete three-dimensional structure of the B12-dependent methyl transfer enzyme complex.
  • To visualize the cofactor's movement and the protein's conformational changes during catalysis.

Main Methods:

  • X-ray crystallography of the complete 220 kDa enzyme complex from Moorella thermoacetica.
  • In crystallo spectroscopic analysis to confirm enzymatic activity.

Main Results:

  • First complete 3D structure of the corrinoid iron-sulfur protein and methyltransferase complex.
  • Visualization of vitamin B12 at multiple positions, revealing protein rearrangements and cofactor trajectory.
  • Demonstration of significant protein conformational changes within crystals, confirming activity.

Conclusions:

  • Provides a structural model for the molecular mechanisms of B12-dependent methyl transfer.
  • Explains the necessity of complex protein machinery for this essential biological reaction.
  • Highlights the largest known protein conformational movements in a crystalline state.