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Related Experiment Videos

Structure-based perspectives on B12-dependent enzymes

M L Ludwig1, R G Matthews

  • 1Biophysics Research Division, University of Michigan, Ann Arbor 48109-1055, USA.

Annual Review of Biochemistry
|January 1, 1997
PubMed
Summary
This summary is machine-generated.

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Cobalamin (B12) proteins undergo conformational changes, with histidine displacing dimethylbenzimidazole. This structural motif is key in cobamide-dependent methyltransferases and methylmalonyl-coenzyme A mutase catalysis.

Area of Science:

  • Biochemistry
  • Structural Biology
  • Enzymology

Background:

  • Cobalamin (B12) is a vital cofactor in numerous enzymatic reactions.
  • X-ray crystallography has provided insights into B12-protein interactions.
  • Specific B12-dependent enzymes include methionine synthase and methylmalonyl-coenzyme A mutase.

Purpose of the Study:

  • To elucidate the structural basis of cobalamin binding in key enzymes.
  • To understand the role of protein-ligand interactions in B12 cofactor function.
  • To identify common structural themes in cobamide-dependent methyltransferases and mutases.

Main Methods:

  • X-ray crystallography of cobalamin bound to methionine synthase and methylmalonyl-coenzyme A mutase.
  • Structural analysis of B12-binding sites and cofactor conformations.

Related Experiment Videos

  • Comparison of B12-protein structures across different organisms and enzyme classes.

    • Main Results:

    • Cobalamin (B12) undergoes significant conformational changes upon binding to apoenzymes.
    • A histidine residue from the protein displaces the dimethylbenzimidazole ligand from the cobalt center in methionine synthase and methylmalonyl-coenzyme A mutase.
    • This histidine ligation is observed in various methyltransferases and B12-dependent mutases, suggesting an emerging structural theme.

    Conclusions:

    • Dimethylbenzimidazole displacement by histidine is a recurring feature in cobamide-dependent methyltransferases, potentially regulating catalytic and activation cycles.
    • While not universal, histidine ligation is present in key B12-dependent mutases like methylmalonyl-coenzyme A mutase, facilitating carbon skeleton rearrangement.
    • The structural motif, including a long cobalt-nitrogen bond, may be crucial for homolytic cleavage of the carbon-cobalt bond in mutase catalysis.