Investigating the interaction between ribonucleoside triphosphosphate reductase and thioredoxin in Lactobacillus leichmannii

Abstract

Ribonucleotide reductases (RNRs) catalyze the conversion of nucleotides to deoxynucleotides (dNTPs) in all organisms and thus play an essential role in DNA biosynthesis and repair. This function makes RNRs attractive targets for anticancer and antiparasitic chemotherapies since inhibition of these enzymes disrupts the dNTP balance within the cell, leading to cell death. Previous work has shown that thioredoxin (Trx)/thioredoxin reductase systems are responsible for the re-reduction of class I and class II RNRs through disulfide exchange reactions involving conserved cysteine residues. To study this re-reduction reaction, we have selected proteins from Lactobacillus leichmannii, an ideal model system due to the relative simplicity of its ribonucleoside triphosphate reductase (RTPR) and the presence of only one Trx in its genome. We have cloned Trx from Lactobacillus leichmannii and purified the protein to homogeneity. To investigate which of the cysteine residues at the C-terminus of RTPR are more reactive toward Trx, we have prepared RTPR mutant proteins C731S and C736S. Further, to investigate which of the cysteines in the conserved Trx ‘CGPC’ motif are more reactive toward RTPR, we have prepared C28S and C31S Trx mutant proteins. Preliminary results of the disulfide-mediated cross-linking of RTPR with Trx will be presented. (Supported by National Institutes of Health GM65337)