Specific derivatization of the active site tyrosine in dUTPase perturbs ligand binding to the active site.

Selective modification of one (of three) tyrosine residue per enzyme monomer leads to inactivation of dUTPase of the retrovirus equine infectious anemia virus (EIAV). The substrate dUMP and the cofactor Mg2+ protect against inactivation and modification, in agreement with the study on E. coli dUTPase (Vertessy et al. (1994) Biochim. Biophys. Acta 1205, 146-150). Amino acid analyses of nitrated dUTPases confirmed Tyr-selectivity of modification. The nitrated residue in E. coli dUTPase was identified as the evolutionary highly conserved Tyr-93. The modifiable residue is shown to be the only Tyr exposed in both E. coli and EIAV dUTPases. As a consequence of Tyr-93 derivatization, the Mg2+-dependent interaction between the substrate-analogue dUDP and E. coli dUTPase becomes impaired as shown by circular dichroism spectroscopy, here presented as a tool for monitoring ligand binding to the active site.