Steve Ealick's Research Group

Streptococcus pyogenes Uridine Phosphorylase

PDB file:



Uridine phosphorylase (UP) is a key enzyme in the pyrimidine salvage pathway and is found in most prokaryotes and eukaryotes. All known UPs belong to the nucleoside phosphorylase I (NP-I) superfamily; however, mammalian UPs are dimers, while bacterial UPs, such as Streptococcus pyogenese UP, are hexamers comprised of a trimer of dimers.  This structure adds to our extensive work on NP-I families including purine nucleoside phosphorylase (bPNP, hPNP, EcPNP, TvPNP), methylthioadenosine phosphorylase (SsMTAP, SsMTAPII and hMTAP), adenosine 5´-monophosphate nucleosidase (AMN) and other uridine phosphorylases (bUP, EcUP and StUP) and 5´-methylthioadenosine/S-adenosylhomocysteine nucleosidase (MTAN).

The SpUP protomer adopts an α/β fold that is very similar to those of the other NP-I enzymes.

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The quaternary structure is hexameric, as are other bacterial UPs, with the trimer of dimers obvious in the structure at the right. Each protomer has an active site; however, the active sites are located at the dimer interface and have residues from each member of the dimer pair.

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The active site of SpUP, shows the bound uracil and ribose 1-phosphate that were isolated under the crystallization conditions.

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Tran TH, Christoffersen S, Allan PW, Parker WB, Piskur J, Serra I, Terreni M, and Ealick SE. The Crystal Structure of Streptococcus pyogenes Uridine Phosphorylase Reveals a Distinct Subfamily of Nucleoside Phosphorylases. Biochemistry 50:6549–6558. (2011).

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