Ribonucleotide reductase subunits

Heidel JD, Liu JY, Yen Y, Zhou B, Heale BS, Rossi JJ, Bartlett DW, Davis ME (2007) Potent siRNA inhibitors of ribonucleotide reductase subunit RRM2 reduce cell proliferation in vitro and in vivo. Clin Cancer Res 13 2207-2215... 

Heidel JD, Yu Z, Liu JY, Rele SM, Liang Y, Zeidan RK, Kombrust DJ, Davis ME (2007) Administration in non-human primates of escalating intravenous doses of targeted nanoparticles containing ribonucleotide reductase subunit M2 siRNA. Proc Natl Acad Sci USA 104 5715-5721... 

We observed longer survival and a trend toward improved response in gemcitabine/ cisplatin-treated stage IV NSCLC patients with low ERCCl mRNA levels (31). A higher response rate was observed in locally advanced NSCLC patients with low levels of ribonucleotide reductase subunit Ml (RRMl) and ERCCl treated with induction gemc-itabine/carboplatin (32). ERCCl protein expression by immunostaining was associated with survival in NSCLC patients treated with cisplatin-based adjuvant therapy (33). 

Climent, L, Sj berg, B.-M., and Huang, C. Y., 1991, Carboxyl-terminal peptides as probes for Escherichia coli ribonucleotide reductase subunit interaction Kinetic analysis of inhibition studies. Biochemistry 30 5164n5171. 

Nguyen, H. H., Ge, J., Perlstein, D. L., and Stubbe, J., 1999, Purification of ribonucleotide reductase subunits Yl, Y2, Y3, and Y4 from yeast Y4 plays a key role in diiron cluster assembly. Proc. Natl. Acad. Sci. USA 96 12339iil2344. 

Rubrerythrin (Rr) was first isolated in 1988 from cellular extracts of D. vulgaris Hildenborough (38), and later also found in D. desulfuri-cans (39). Rr is constituted by two identical subunits of 22 kDa and it was shown that each monomer contains one Rd-like center, Fe(RS)4, and a diiron-oxo center similar to the ones found in methane monooxygenase (MMO) (40, 41) or ribonucleotide reductase (RNR-R2) (42). After aerobic purification, the UV-visible spectrum shows maxima at 492, 365, and 280 nm, and shoulders at 570 and 350 nm. This spectrum is similar to the ones observed for Rd proteins. From a simple subtraction of a typical Rd UV-vis spectrum (normalized to 492 nm) it is possible to show that the remainder of the spectrum (maxima at 365 nm and a shoulder at 460 nm) strongly resembles the spectrum of met-hemerythrin, another diiron-oxo containing protein. 

Metalloenzymes with non-heme di-iron centers in which the two irons are bridged by an oxide (or a hydroxide) and carboxylate ligands (glutamate or aspartate) constitute an important class of enzymes. Two of these enzymes, methane monooxygenase (MMO) and ribonucleotide reductase (RNR) have very similar di-iron active sites, located in the subunits MMOH and R2 respectively. Despite their structural similarity, these metal centers catalyze very different chemical reactions. We have studied the enzymatic mechanisms of these enzymes to understand what determines their catalytic activity [24, 25, 39-41]. 

Massie, B., Dionne, J., Lamarche, N. et al. (1995) Improved adenovirus vector provides herpes simplex virus ribonucleotide reductase R1 and R2 subunits very efficiently. Bio/Technology (Nature Publishing Company), 13 (6), 602-608. 

M. Bennati, A. Weber, J. Antonie, D.L. Perlstein, J. Robblee and J. Stubbe, Pulsed ELDOR spectroscopy measures the distance between the two tyrosyl radicals in the R2 subunit of the E. coli ribonucleotide reductase, J. Am. Chem. Soc., 2003, 125, 14988. 

Based on these findings and toxicology studies [233], human clinical phase I studies have been initiated [234]. In tumor biopsies from melanoma patients obtained after treatment, a reduction was found in both the specific mRNA (M2 subunit of ribonucleotide reductase, RRM2) and in the protein (RRM2) levels when compared to pre-dosed tissue. The presence of an mRNA fragment that... 

Langen, P., Quenching of tyrosine radicals of M2 subunit from ribonucleotide reductase in tumor cells by different antitumor agents an EPR study, Free Radical Biol. Med. 9 (1990), p. 1-4... 

Interest in this class of coordination compounds was sparked and fueled by the discovery that radical cofactors such as tyrosyl radicals play an important role in a rapidly growing number of metalloproteins. Thus, in 1972 Ehrenberg and Reichard (1) discovered that the R2 subunit of ribonucleotide reductase, a non-heme metal-loprotein, contains an uncoordinated, very stable tyrosyl radical in its active site. In contrast, Whittaker and Whittaker (2) showed that the active site of the copper containing enzyme galactose oxidase (GO) contains a radical cofactor where a Cu(II) ion is coordinated to a tyrosyl radical. 

Figure 13.25 Three-dimensional structures of diiron proteins. The iron-binding subunits of (a) haemery-thrin, (b) bacterioferritin, (c) rubryerythrin (the FeS centre is on the top), (d) ribonucleotide reductase R2 subunit, (e) stearoyl-acyl carrier protein A9 desaturase, (f) methane monooxygenase hydroxylase a-subunit. (From Nordlund and Eklund, 1995. Copyright 1995, with permission from Elsevier.)...

Initial insight of the role of CSN in cell-cycle control came from the finding that csnl and csn2 deletion S. pomhe strains have an S-phase delay [52]. Interestingly, this effect did not occur in strains missing other CSN subunits. The S-phase delay was caused by the accumulation of the cell-cycle inhibitor Spdl (S-phase delayed 1), which is involved in the misregulation of the ribonucleotide reductase (RNR). RNR catalyzes the production of deoxyribonucleotides for DNA synthesis and... 

Liu, C., Powell, K. A., Mundt, K., Wu, L., Care, A. M., Caspaei, T. Cop9/signalosome subunits and Pcu4 regulate ribonucleotide reductase by both checkpoint-dependent and -independent mechanisms. Genes Dev. 2003, 17, 1130-1140. 

Figure 3. First shell (1.1-2.3A) EXAFS spectra of methemerythrin azide, semimethemerythrin azide, ribonucleotide reductase B2 subunit, oxidized uteroferrin-phosphate complex, and reduced uteroferrin.

In eukaryotes, ribonucleotide reductase is a tetramer consisting of two R1 and two R2 subunits. In addition to the disulfide bond mentioned, a tyrosine radical in the enzyme also participates in the reaction (2). It initially produces a substrate radical (3). This cleaves a water molecule and thereby becomes radical cation. Finally, the deoxyribose residue is produced by reduction, and the tyrosine radical is regenerated. 

The regulation of ribonucleotide reductase is complex. The substrate-specificity and activity of the enzyme are controlled by two allosteric binding sites (a and b) in the R1 subunits. ATP and dATP increase or reduce the activity of the reductase by binding at site a. Other nucleotides interact with site b, and thereby alter the enzyme s specificity. 

Ask A, Persson L, Rehnholm A, Frostesjo L, Holm I, Heby O (1993) Development of resistance to hydroxyurea during treatment of human myelogenous leukemia K562 cells with alpha-difluoromethylornithine as a result of coamplification of genes for ornithine decarboxylase and ribonucleotide reductase R2 subunit. Cancer Res 53 5262-5268... 

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