Open AccessReactivity of the Tyrosyl Radical of Escherichia Coli Ribonucleotide Reductase
Author(s) -
Gerez Catherine,
Elleingand Eric,
Kauppi Björn,
Eklund Hans,
Fontecave Marc
Publication year - 1997
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1997.t01-2-00401.x
Subject(s) - ribonucleotide reductase , chemistry , reactivity (psychology) , sodium dithionite , dithionite , radical , enzyme , radical ion , stereochemistry , combinatorial chemistry , biochemistry , organic chemistry , medicine , ion , alternative medicine , pathology , protein subunit , gene
Ribonucleotide reductase is a key enzyme for DNA synthesis. Its small component, named protein R2, contains a tyrosyl radical essential for activity. Consequently, radical scavengers are potential antiproliferative agents. In this study, we show that the reactivity of the tyrosyl radical towards phenols, hydrazines, hydroxyurea, dithionite and ascorbate can be finely tuned by relatively small modifications of its hydrophobic close environment. For example, in this hydrophobic pocket, Leu77→Phe mutation resulted in a protein with a much higher susceptibility to radical scavenging by hydrophobic agents. This might suggest that the protein is flexible enough to allow small molecules to penetrate in the radical site. When mutations keeping the hydrophobic character are brought further from the radical (for example IIe74→Phe) the reactivity of the radical is instead very little affected. When a positive charge was introduced (for example IIe74→Arg or Lys) the protein was more sensitive to negatively charged electron donors such as dithionite. These results allow us to understand how tyrosyl radical sites have been optimized to provide a good stability for the free radical.