Crystal structure of vaccinia virus uracil-DNA glycosylase reveals dimeric assembly.
BACKGROUND
Uracil-DNA glycosylases (UDGs) catalyze excision of uracil from DNA. Vaccinia virus, which is the prototype of poxviruses, encodes a UDG (vvUDG) that is significantly different from the UDGs of other organisms in primary, secondary and tertiary structure and characteristic motifs. It adopted a novel catalysis-independent role in DNA replication that involves interaction with a viral protein, A20, to form the processivity factor. UDG:A20 association is essential for assembling of the processive DNA polymerase complex. The structure of the protein must have provisions for such interactions with A20. This paper provides the first glimpse into the structure of a poxvirus UDG.


RESULTS
Results of dynamic light scattering experiments and native size exclusion chromatography showed that vvUDG is a dimer in solution. The dimeric assembly is also maintained in two crystal forms. The core of vvUDG is reasonably well conserved but the structure contains one additional beta-sheet at each terminus. A glycerol molecule is found in the active site of the enzyme in both crystal forms. Interaction of this glycerol molecule with the protein possibly mimics the enzyme-substrate (uracil) interactions.


CONCLUSIONS
The crystal structures reveal several distinctive features of vvUDG. The new structural features may have evolved for adopting novel functions in the replication machinery of poxviruses. The mode of interaction between the subunits in the dimers suggests a possible model for binding to its partner and the nature of the processivity factor in the polymerase complex.
Schormann
Norbert
N
Center for Biophysical Sciences & Engineering, University of Alabama at Birmingham, Birmingham, AL 35294, USA. nschorm@uab.edu <nschorm@uab.edu>
Grigorian
Alexei
A
Samal
Alexandra
A
Krishnan
Raman
R
DeLucas
Lawrence
L
Chattopadhyay
Debasish
D
D000595:Amino Acid Sequence; D001665:Binding Sites; D003460:Crystallization; D018360:Crystallography, X-Ray; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D040681:Structural Homology, Protein; D051981:Uracil-DNA Glycosidase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014616:Vaccinia virus / Q000201:enzymology*; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D014764:Viral Proteins; D051981:Uracil-DNA Glycosidase