Journal
BIOCHEMISTRY
Volume 47, Issue 21, Pages 5755-5766Publisher
AMER CHEMICAL SOC
DOI: 10.1021/bi800132d
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Funding
- NIAMS NIH HHS [R01 AR035186, AR35186] Funding Source: Medline
- NIGMS NIH HHS [T32 GM008505, T32-GM008505, R01-GM40313, R01 GM040313] Funding Source: Medline
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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.
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