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Molybdopterin biosynthesis: trapping of intermediates for the MoaA-catalyzed reaction using 2'-deoxyGTP and 2'-chloroGTP as substrate analogues.

Mehta AP, Abdelwahed SH, Xu H, Begley TP - J. Am. Chem. Soc. (2014)

Bottom Line: MoaA is a radical S-adenosylmethionine (AdoMet) enzyme that catalyzes a complex rearrangement of guanosine-5'-triphosphate (GTP) in the first step of molybdopterin biosynthesis.In this paper, we provide additional characterization of the MoaA reaction product, describe the use of 2'-chloroGTP to trap the GTP C3' radical, generated by hydrogen atom transfer to the 5'-deoxyadenosyl radical, and the use of 2'-deoxyGTP to block a late step in the reaction sequence.These probes, coupled with the previously reported trapping of an intermediate in which C3' of the ribose is linked to C8 of the purine, allow us to propose a plausible mechanism for the MoaA-catalyzed reaction.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Texas A & M University , College Station, Texas 77843, United States.

ABSTRACT
MoaA is a radical S-adenosylmethionine (AdoMet) enzyme that catalyzes a complex rearrangement of guanosine-5'-triphosphate (GTP) in the first step of molybdopterin biosynthesis. In this paper, we provide additional characterization of the MoaA reaction product, describe the use of 2'-chloroGTP to trap the GTP C3' radical, generated by hydrogen atom transfer to the 5'-deoxyadenosyl radical, and the use of 2'-deoxyGTP to block a late step in the reaction sequence. These probes, coupled with the previously reported trapping of an intermediate in which C3' of the ribose is linked to C8 of the purine, allow us to propose a plausible mechanism for the MoaA-catalyzed reaction.

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Firststeps in molybdopterin biosynthesis: (A) The carbon-labelingpattern for the conversion of GTP 1 to cyclic pyranopterinmonophosphate 2. (B) Initial mechanistic proposal forthe MoaA/MoaC-catalyzed reaction.5,6
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fig1: Firststeps in molybdopterin biosynthesis: (A) The carbon-labelingpattern for the conversion of GTP 1 to cyclic pyranopterinmonophosphate 2. (B) Initial mechanistic proposal forthe MoaA/MoaC-catalyzed reaction.5,6

Mentions: Molybdopterin is aredox cofactor used by enzymes such as xanthineoxidase, sulfite oxidase, nitrate reductase, carbon monoxide dehydrogenaseand formate dehydrogenase.1 Previous studieshave established that the C8 carbon of GTP 1 is insertedinto the C2′-C3′ bond of the GTP ribose in a reactioncatalyzed by MoaA–MoaC (Figure 1A).2 MoaA is a radical SAM enzyme that utilizes two[4Fe-4S] clusters. EPR and structural studies show that these clustersinteract with the purine of GTP and the amino acid of SAM.3,4 A mechanistic proposal, based on the identification of the initiallyabstracted hydrogen atom and the trapping of intermediate 8 is outlined in Figure 1B.5−7


Molybdopterin biosynthesis: trapping of intermediates for the MoaA-catalyzed reaction using 2'-deoxyGTP and 2'-chloroGTP as substrate analogues.

Mehta AP, Abdelwahed SH, Xu H, Begley TP - J. Am. Chem. Soc. (2014)

Firststeps in molybdopterin biosynthesis: (A) The carbon-labelingpattern for the conversion of GTP 1 to cyclic pyranopterinmonophosphate 2. (B) Initial mechanistic proposal forthe MoaA/MoaC-catalyzed reaction.5,6
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4227724&req=5

fig1: Firststeps in molybdopterin biosynthesis: (A) The carbon-labelingpattern for the conversion of GTP 1 to cyclic pyranopterinmonophosphate 2. (B) Initial mechanistic proposal forthe MoaA/MoaC-catalyzed reaction.5,6
Mentions: Molybdopterin is aredox cofactor used by enzymes such as xanthineoxidase, sulfite oxidase, nitrate reductase, carbon monoxide dehydrogenaseand formate dehydrogenase.1 Previous studieshave established that the C8 carbon of GTP 1 is insertedinto the C2′-C3′ bond of the GTP ribose in a reactioncatalyzed by MoaA–MoaC (Figure 1A).2 MoaA is a radical SAM enzyme that utilizes two[4Fe-4S] clusters. EPR and structural studies show that these clustersinteract with the purine of GTP and the amino acid of SAM.3,4 A mechanistic proposal, based on the identification of the initiallyabstracted hydrogen atom and the trapping of intermediate 8 is outlined in Figure 1B.5−7

Bottom Line: MoaA is a radical S-adenosylmethionine (AdoMet) enzyme that catalyzes a complex rearrangement of guanosine-5'-triphosphate (GTP) in the first step of molybdopterin biosynthesis.In this paper, we provide additional characterization of the MoaA reaction product, describe the use of 2'-chloroGTP to trap the GTP C3' radical, generated by hydrogen atom transfer to the 5'-deoxyadenosyl radical, and the use of 2'-deoxyGTP to block a late step in the reaction sequence.These probes, coupled with the previously reported trapping of an intermediate in which C3' of the ribose is linked to C8 of the purine, allow us to propose a plausible mechanism for the MoaA-catalyzed reaction.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Texas A & M University , College Station, Texas 77843, United States.

ABSTRACT
MoaA is a radical S-adenosylmethionine (AdoMet) enzyme that catalyzes a complex rearrangement of guanosine-5'-triphosphate (GTP) in the first step of molybdopterin biosynthesis. In this paper, we provide additional characterization of the MoaA reaction product, describe the use of 2'-chloroGTP to trap the GTP C3' radical, generated by hydrogen atom transfer to the 5'-deoxyadenosyl radical, and the use of 2'-deoxyGTP to block a late step in the reaction sequence. These probes, coupled with the previously reported trapping of an intermediate in which C3' of the ribose is linked to C8 of the purine, allow us to propose a plausible mechanism for the MoaA-catalyzed reaction.

Show MeSH
Related in: MedlinePlus