Cloning and characterization of the R1 and R2 subunits of ribonucleotide reductase from Trypanosoma brucei

被引:52
作者
Hofer, A [1 ]
Schmidt, PP [1 ]
Graslund, A [1 ]
Thelander, L [1 ]
机构
[1] UNIV STOCKHOLM, ARRHENIUS LAB, DEPT BIOPHYS, S-10691 STOCKHOLM, SWEDEN
关键词
D O I
10.1073/pnas.94.13.6959
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
Ribonucleotide reductase (RNR) catalyzes the rate limiting step in the de novo synthesis of deoxyribonucleotides by directly reducing ribonucleotides to the corresponding deoxyribonucleotides. To keep balanced pools of deoxyribonucleotides, all nonviral RNRs studied so far are allosterically regulated, Most eukaryotes contain a class I RNR, which is a heterodimer of two nonidentical subunits called proteins R1 and R2, We have isolated cDNAs encoding the R1 and R2 proteins from Trypanosoma brucei. The amino acid sequence identities with the mouse R1 and R2 subunits are 58% and 63%, respectively, Recombinant active trypanosome R1 and R2 proteins were expressed in Escherichia coli and purified, The R2 protein contains an iron-tyrosyl free radical center verified by EPR spectroscopy and iron analyses, Measurement of cytidine 5'-diphosphate reduction by the trypanosome RNR in the presence of various allosteric effecters showed that the activity is highest with dTTP, dGTP, or dATP and considerably lower with ATP. The effect of dGTP is either activating (alone) or inhibitory (in the presence of ATP), Filter binding studies indicated that there are two classes of allosteric effector binding sites that bind ATP or dATP (low-affinity dATP site) and ATP, dATP, dGTP, or dTTP (high-affinity dATP site), respectively, Therefore, the structural organization of the allosteric sites is very similar to the mammalian RNRs, whereas the allosteric regulation of cytidine 5'-diphosphate reduction is unique, Hopefully, this difference can be used to target the trypanosome RNR for therapeutic purposes.
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页码:6959 / 6964
页数:6
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