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Related Concept Videos

Cofactors and Coenzymes01:27

Cofactors and Coenzymes

Enzymes require additional components for proper function. There are two such classes of molecules: cofactors and coenzymes. Cofactors are metallic ions and coenzymes are non-protein organic molecules. Both of these types of helper molecule can be tightly bound to the enzyme or bound only when the substrate binds.
Cofactors and Coenzymes01:24

Cofactors and Coenzymes

Enzymes are proteins made of amino acids. The functional group of each constituent amino acid catalyzes a wide variety of chemical reactions via ionic interactions or acid-base reactions. However, amino acids cannot catalyze oxidation-reduction and group transfer reactions and need to be aided by non-protein components called cofactors. Cofactors are also referred to as the chemical teeth of an enzyme.
Cofactors can be metallic ions or organic molecules called coenzymes. These types of helper...
Cofactors and Coenzymes01:27

Cofactors and Coenzymes

Enzymes require additional components for proper function. There are two such classes of molecules: cofactors and coenzymes. Cofactors are metallic ions and coenzymes are non-protein organic molecules. Both of these types of helper molecule can be tightly bound to the enzyme or bound only when the substrate binds.
Protein Complexes with Interchangeable Parts01:57

Protein Complexes with Interchangeable Parts

Groups of proteins may form a complex where each protein in this complex has a different role in the overall execution of the complex’s function. Often some of the proteins in the complex can be replaced by a closely related variant to give a complex that contains many of the same components yet is functionally distinct.
The SCF ubiquitin ligase is a protein complex of five individual proteins. This complex attaches ubiquitin to other target proteins to mark them for degradation. In order to...
Protein Complexes with Interchangeable Parts01:57

Protein Complexes with Interchangeable Parts

Groups of proteins may form a complex where each protein in this complex has a different role in the overall execution of the complex’s function. Often some of the proteins in the complex can be replaced by a closely related variant to give a complex that contains many of the same components yet is functionally distinct.
The SCF ubiquitin ligase is a protein complex of five individual proteins. This complex attaches ubiquitin to other target proteins to mark them for degradation. In order to...
Ligand Binding and Linkage00:49

Ligand Binding and Linkage

Allosteric proteins have more than one ligand binding site; the binding of a ligand to any of these sites influences the binding of ligands to the other sites. When a protein is allosteric, its binding sites are called coupled or linked.  In the case of enzymes, the site that binds to the substrate is known as the active site and the other site is known as the regulatory site. When a ligand binds to the regulatory site, this leads to conformational changes in the protein that can influence the...

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Related Experiment Video

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The MultiBac Protein Complex Production Platform at the EMBL
13:51

The MultiBac Protein Complex Production Platform at the EMBL

Published on: July 11, 2013

Structural basis of multifunctionality in a vitamin B12-processing enzyme.

Markos Koutmos1, Carmen Gherasim, Janet L Smith

  • 1Department of Biological Chemistry and the Life Sciences Institute, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0600, USA.

The Journal of Biological Chemistry
|June 24, 2011
PubMed
Summary

Researchers uncovered the structure of human CblC, an enzyme crucial for vitamin B12 processing. This reveals how CblC uniquely handles different vitamin forms and explains genetic disorders like homocystinuria.

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Sequence-specific Labeling of Nucleic Acids and Proteins with Methyltransferases and Cofactor Analogues

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Area of Science:

  • Biochemistry
  • Structural Biology
  • Enzymology

Background:

  • Intracellular vitamin B12 processing involves CblC, an enzyme with dual catalytic functions.
  • CblC is the most common site for mutations causing inherited cobalamin disorders, leading to homocystinuria and methylmalonic aciduria.

Purpose of the Study:

  • To elucidate the structural basis for CblC's dual reactivity in vitamin B12 metabolism.
  • To provide biochemical insights into the mechanism of action of human CblC.
  • To rationalize the impact of pathological mutations on CblC function and associated diseases.

Main Methods:

  • X-ray crystallography to determine the structures of human CblC, both apo and holo (bound to methylcobalamin).
  • Biochemical assays to investigate CblC's enzymatic activities and cofactor usage.

Main Results:

  • Novel structures of human CblC reveal its unique scaffold supporting dual catalytic activities.
  • CblC is a divergent member of the NADPH-dependent flavin reductase family, utilizing FMN or FAD for reductive decyanation.
  • CblC exhibits glutathione transferase activity, unrelated to the known GST superfamily, highlighting evolutionary adaptation.

Conclusions:

  • The CblC structure provides a mechanistic understanding of its dual reactivity in vitamin B12 metabolism.
  • CblC represents a unique example of a single enzyme scaffold adapted for diverse biochemical functions.
  • The structural insights explain the biochemical basis of severe inherited cobalamin disorders linked to CblC mutations.