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 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.
St Maurice
Martin
M
Departments of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
Mera
Paola
P
Park
Kiyoung
K
Brunold
Thomas C
TC
Escalante-Semerena
Jorge C
JC
Rayment
Ivan
I
D000255:Adenosine Triphosphate / Q000737:chemistry; D019883:Alkyl and Aryl Transferases / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry*; D001665:Binding Sites; D001671:Biochemistry / Q000379:methods; D002384:Catalysis; D002942:Circular Dichroism; D003038:Cobamides / Q000737:chemistry*; D045728:Corrinoids / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006801:Humans; D007700:Kinetics; D052200:Limosilactobacillus reuteri / Q000201:enzymology; D017434:Protein Structure, Tertiary; D019779:Salmonella enterica / Q000201:enzymology; D013053:Spectrophotometry / Q000379:methods
D001426:Bacterial Proteins; D003038:Cobamides; D045728:Corrinoids; D000255:Adenosine Triphosphate; D019883:Alkyl and Aryl Transferases; C082269:ATP-corrinoid adenosyltransferase; C000913:cobamamide