Structural Characterization of a Human-Type Corrinoid Adenosyltransferase Confirms That Coenzyme B12 Is Synthesized through a Four-Coordinate Intermediate

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 B12. For the ACA-catalyzed reaction to proceed, cob(II)alamin must be reduced to cob(I)alamin in the enzyme active s...

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Bibliographic Details
Published in:Biochemistry (Easton) 2008-05, Vol.47 (21), p.5755-5766
Main Authors: St. Maurice, Martin, Mera, Paola, Park, Kiyoung, Brunold, Thomas C, Escalante-Semerena, Jorge C, Rayment, Ivan
Format: Article
Language:English
Subjects:
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
Lactobacillus reuteri - enzymology
Protein Structure, Tertiary
Salmonella enterica - enzymology
Spectrophotometry - methods
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Summary: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 B12. 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 B12. 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.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi800132d