NDLI: Peroxyl adduct radicals formed in the iron/oxygen reconstitution reaction of mutant ribonucleotide reductase R2 proteins from Escherichia coli

Content Provider	Springer Nature Link
Author	Sahlin, Margareta Cho, Kyung Bin Pötsch, Stephan Lytton, Simon D. Huque, Yasmin Gunther, Michael R. Sjöberg, Britt Marie Mason, Ronald P. Gräslund, Astrid
Copyright Year	2001
Abstract	Catalytically important free radicals in enzymes are generally formed at highly specific sites, but the specificity is often lost in point mutants where crucial residues have been changed. Among the transient free radicals earlier found in the Y122F mutant of protein R2 in Escherichia coli ribonucleotide reductase after reconstitution with Fe2+ and O2, two were identified as tryptophan radicals. A third radical has an axially symmetric EPR spectrum, and is shown here using 17O exchange and simulations of EPR spectra to be a peroxyl adduct radical. Reconstitution of other mutants of protein R2 (i.e. Y122F/W48Y and Y122F/W107Y) implicates W48 as the origin of the peroxyl adduct. The results indicate that peroxyl radicals form on primary transient radicals on surface residues such as W48, which is accessible to oxygen. However, the specificity of the reaction is not absolute since the single mutant W48Y also gives rise to a peroxyl adduct radical. We used density functional calculations to investigate residue-specific effects on hyperfine coupling constants using models of tryptophan, tyrosine, glycine and cysteine. The results indicate that any peroxyl adduct radical attached to the first three amino acid α-carbons gives similar 17O hyperfine coupling constants. Structural arguments and experimental results favor W48 as the major site of peroxyl adducts in the mutant Y122F. Available molecular oxygen can be considered as a spin trap for surface-located protein free radicals.
Starting Page	74
Ending Page	82
Page Count	9
File Format	PDF
ISSN	09498257
Journal	JBIC Journal of Biological Inorganic Chemistry
Volume Number	7
Issue Number	1-2
e-ISSN	14321327
Language	English
Publisher	Springer Berlin Heidelberg
Publisher Date	2001-07-27
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Biochemistry Microbiology
Content Type	Text
Resource Type	Article
Subject	Biochemistry Inorganic Chemistry

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