5r1r
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RIBONUCLEOTIDE REDUCTASE E441A MUTANT R1 PROTEIN FROM ESCHERICHIA COLI
OverviewOverview
The invariant active site residue Glu441 in protein R1 of ribonucleotide, reductase from Escherichia coli has been engineered to alanine, aspartic, acid, and glutamic acid. Each mutant protein was structurally and, enzymatically characterized. Glu441 contributes to substrate binding, and, a carboxylate side chain at position 441 is essential for catalysis. The, most intriguing results are the suicidal mechanism-based reaction, intermediates observed when R1 E441Q is incubated with protein R2 and, natural substrates (CDP and GDP). In a consecutive reaction sequence, we, observe at least three clearly discernible steps: (i) a rapid decay (k1, >/= 1.2 s-1) of the catalytically essential tyrosyl radical of protein R2, concomitant with formation of an early transient radical intermediate, species, (ii) a slower decay (k2 = 0.03 s-1) of the early intermediate, concomitant with formation of another intermediate with a triplet EPR, signal, and (iii) decay (k3 = 0.004 s-1) of the latter concomitant with, formation of a characteristic substrate degradation product. The, characteristics of the triplet EPR signal are compatible with a substrate, radical intermediate (most likely localized at the 3'-position of the, ribose moiety of the substrate nucleotide) postulated to occur in the wild, type reaction mechanism as well.
About this StructureAbout this Structure
5R1R is a Protein complex structure of sequences from Escherichia coli. Active as Ribonucleoside-diphosphate reductase, with EC number 1.17.4.1 Structure known Active Sites: ACA, ACB and ACC. Full crystallographic information is available from OCA.
ReferenceReference
A new mechanism-based radical intermediate in a mutant R1 protein affecting the catalytically essential Glu441 in Escherichia coli ribonucleotide reductase., Persson AL, Eriksson M, Katterle B, Potsch S, Sahlin M, Sjoberg BM, J Biol Chem. 1997 Dec 12;272(50):31533-41. PMID:9395490
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