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+protects against inactivation and modification, in agreement with the study onE. colidUTPase (Vertessyet al.(1994)Biochim. Biophys. Acta1205, 146-150). Amino acid analyses of nitrated dUTPases confirmed Tyr-selectivity of modification. The nitrated residue inE. colidUTPase was identified as the evolutionary highly conserved Tyr-93. The modifiable residue is shown to be the only Tyr exposed in bothE. coliand EIAV dUTPases. As a consequence of Tyr-93 derivatization, the Mg2+-dependent interaction between the substrate-analogue dUDP andE. colidUTPase becomes impaired as shown by circular dichroism spectroscopy, here presented as a tool for monitoring ligand binding to the active site.