Chloroviruses encode a bifunctional dCMP-dCTP deaminase that produces two key intermediates in dTTP formation.
The chlorovirus PBCV-1, like many large double-stranded DNA-containing viruses, contains several genes that encode putative proteins involved in nucleotide biosynthesis. This report describes the characterization of the PBCV-1 dCMP deaminase, which produces dUMP, a key intermediate in the synthesis of dTTP. As predicted, the recombinant protein has dCMP deaminase activity that is activated by dCTP and inhibited by dTTP. Unexpectedly, however, the viral enzyme also has dCTP deaminase activity, producing dUTP. Typically, these two reactions are catalyzed by proteins in separate enzyme classes; to our knowledge, this is the first example of a protein having both deaminase activities. Kinetic experiments established that (i) the PBCV-1 enzyme has a higher affinity for dCTP than for dCMP, (ii) dCTP serves as a positive heterotropic effector for the dCMP deaminase activity and a positive homotropic effector for the dCTP deaminase activity, and (iii) the enzymatic efficiency of the dCMP deaminase activity is about four times higher than that of the dCTP deaminase activity. Inhibitor studies suggest that the same active site is involved in both dCMP and dCTP deaminations. The discovery that the PBCV-1 dCMP deaminase has two activities, together with a previous report that the virus also encodes a functional dUTP triphosphatase (Y. Zhang, H. Moriyama, K. Homma, and J. L. Van Etten, J. Virol. 79:9945-9953, 2005), means that PBCV-1 is the first virus to encode enzymes involved in all three known pathways to form dUMP.
Zhang
Yuanzheng
Y
Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, NE 68583-0722, USA.
Maley
Frank
F
Maley
Gladys F
GF
Duncan
Garry
G
Dunigan
David D
DD
Van Etten
James L
JL
D000595:Amino Acid Sequence; D001483:Base Sequence; D002708:Chlorella / Q000821:virology; D003001:Cloning, Molecular; D003844:DCMP Deaminase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017931:DNA Primers; D007700:Kinetics; D008969:Molecular Sequence Data; D009709:Nucleotide Deaminases / Q000235:genetics* / Q000378:metabolism; D017862:Phycodnaviridae / Q000201:enzymology*; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid; D013942:Thymine Nucleotides / Q000096:biosynthesis*
D017931:DNA Primers; D013942:Thymine Nucleotides; D009709:Nucleotide Deaminases; D003844:DCMP Deaminase; C019988:dCTP deaminase; C024157:thymidine 5'-triphosphate