STRUCTURE AND FUNCTION OF RIBONUCLEOTIDE REDUCTASE R1 PROTEIN. Eriksson. M., Ramaswamy. S., Uhlin. U. and Eklund H., Department of Molecular Biology, Biomedical Center, Swedish Univ. Of Agricultural Sciences, Uppsala, 75124. SWEDEN.

The effector binding site, the reduced and the oxidised forms of the large subunit of the R1 protein of Ribonucleotide Reductase (RR1) and the refinement of the native protein is the subject of this abstract. RR1 is the enzyme that catalyses the reaction of all the four ribonucleotides into its corresponding deoxy form. The enzyme is therefore very crucial in the synthesis of the precursor molecules of DNA. The enzyme is an [[alpha]]₂-[[beta]]₂ enzyme. One subunit called the R2 or the smaller subunit has the di-iron center and generates the free-radical which is required for its activity, the other subunit R1, is the larger subunit and houses the active site and the alloesteric sites. The structures of both these have been determined and published earlier.

We have now refined the structure of the R1 protein at 2.5Å resolution with strict ncs symmetry. The final R-factor is 21%. We also have determined the structure of various mutants of this enzyme and refined them. One of the mutants Y730F, has the catalytic disulphide in the reduced form. A structure has also been determined which has the effector bound to it. These have enabled us to further our understanding of the mode of action of this subunit. We have also docked the two subunits and have now a hypothetical model for the possible mode of transfer of the free-radical from one subunit to the other. The results of these studies will be presented.