Structural characterization of a human-type corrinoid adenosyltransferase confirms that coenzyme B12 is synthesized through a four-coordinate intermediate

Biochemistry. 2008 May 27;47(21):5755-66. doi: 10.1021/bi800132d. Epub 2008 May 2.


ATP:cob(I)alamin adenosyltransferases (ACAs) catalyze the transfer of the 5'-deoxyadenosyl moiety from ATP to the upper axial ligand position of cobalamin in the synthesis of coenzyme B 12. For the ACA-catalyzed reaction to proceed, cob(II)alamin must be reduced to cob(I)alamin in the enzyme active site. This reduction is facilitated through the generation of a four-coordinate cob(II)alamin intermediate on the enzyme. We have determined the high-resolution crystal structure of a human-type ACA from Lactobacillus reuteri with a four-coordinate cob(II)alamin bound in the enzyme active site and with the product, adenosylcobalamin, partially occupied in the active site. The assembled structures represent snapshots of the steps in the ACA-catalyzed formation of the cobalt-carbon bond of coenzyme B 12. The structures define the corrinoid binding site and provide visual evidence for a base-off, four-coordinate cob(II)alamin intermediate. The complete structural description of ACA-mediated catalysis reveals the molecular features of four-coordinate cob(II)alamin stabilization and provides additional insights into the molecular basis for dysfunction in human patients suffering from methylmalonic aciduria.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adenosine Triphosphate / chemistry
  • Alkyl and Aryl Transferases / chemistry*
  • Bacterial Proteins / chemistry*
  • Binding Sites
  • Biochemistry / methods
  • Catalysis
  • Circular Dichroism
  • Cobamides / chemistry*
  • Corrinoids / chemistry*
  • Crystallography, X-Ray
  • Humans
  • Kinetics
  • Limosilactobacillus reuteri / enzymology
  • Protein Structure, Tertiary
  • Salmonella enterica / enzymology
  • Spectrophotometry / methods


  • Bacterial Proteins
  • Cobamides
  • Corrinoids
  • Adenosine Triphosphate
  • Alkyl and Aryl Transferases
  • ATP-corrinoid adenosyltransferase
  • cobamamide

Associated data

  • PDB/3CI1
  • PDB/3CI3
  • PDB/3CI4