Steve Ealick's Research Group

Grouper Iridovirus Purine Nucleoside Phosphorylase

PDB file:



Purine nucleoside phosphorylase (PNP) catalyzes the reversible phosphorolysis of purine ribonucleosides to the corresponding free bases and ribose 1-phosphate. The iridovirus that infects grouper fish represents the first instance in which the PNP gene has been found in a virus.

The core of the givPNP protomer has an α/β structure with a nine-stranded mixed β-barrel surrounded by four α-helices on one side and five on the other side.


Click the image to enlarge.

The overall structure of givPNP is a homotrimer that is similar to the structures of human PNP and bovine PNP. In givPNP, there is a disulfide bond between Cys203 and Cys246 in a flexible loop region. The rigid disulfide bond alters the first part of this loop resulting in a conformation different from the mammalian PNPs.

Click the image to enlarge.

The active sites, which are located at the trimer interface and formed by residues from two adjacent protomers, are occupied by a phosphate ion and a Tris molecule.


Click the image to enlarge.


Kang YN, Zhang Y, Allan PW, Parker WB, Ting JW, Chang CY and Ealick SE. Crystal Structure of Grouper Iridovirus Purine Nucleoside Phosphorylase.Acta Crystallogr. D 66:155-162 (2010).

Contacts Procedures Structures Projects Publications Lab Home Page Group Members