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The Radical Site in Chlamydial Ribonucleotide Reductase Defines a New R2 Subclass
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
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2004 In: Science, ISSN 0036-8075, Vol. 305, no 5681, 245-248 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
2004. Vol. 305, no 5681, 245-248 p.
Identifiers
URN: urn:nbn:se:su:diva-24050OAI: oai:DiVA.org:su-24050DiVA: diva2:196599
Note
Part of urn:nbn:se:su:diva-652Available from: 2005-09-07 Created: 2005-09-07Bibliographically approved
In thesis
1. Paramagnetic states of diiron carboxylate proteins
Open this publication in new window or tab >>Paramagnetic states of diiron carboxylate proteins
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diiron carboxylate proteins constitute an important class of metall-containing enzymes. These proteins perform a multitude of reactions in biological systems that normally involve activation of molecular oxygen at the diiron site.

During activation and functioning of these proteins their diiron sites undergo redox changes in a rather wide range: from diferrous (FeII-FeII) to high potential intermediate Q(FeIV-FeIV). Two of these redox states are paramagnetic: (FeIV-FeIII), called high potential intermediate X, and (FeII-FeIII), called mixed-valent state of the diiron carboxylate proteins. In the present work it has been shown that these redox states are of functional relevance in two proteins with different functions.

Ribonucleotide reductase (RNR) from the human parasite Chlamydia trachomatis is a class I RNR. It is typical for class I RNR to initiate the enzymatic reaction on its large subunit, protein R1, by activation from a stable tyrosyl free radical in its small subunit, protein R2. This radical, in its turn, is formed through oxygen activation by the diiron center. In C. trachomatis the tyrosine residue is replaced by phenylalanine, which cannot form a radical. We have shown in the present work, that active C. trachomatis RNR uses the FeIII-FeIV state of the diiron carboxylate cluster in R2 instead of a tyrosyl radical to initiate the catalytic reaction.

The alternative oxidase (AOX) is a ubiquinol oxidase found in the mitochondrial respiratory chain of plants. The existence of the diiron carboxylate center in this protein was predicted on the basis of a conserved sequence motif consisting of the proposed iron ligands, four glutamate and two histidine residues. In experiments modeling the conditions of the enzyme catalytic cycle, i.e. reduction and reoxygenation of the overexpressed AOX in Escherichia coli membranes we were able to generate an EPR signal characteristic of a mixed-valent Fe(II)/Fe(III) binuclear iron center. The alternative oxidase is the first membrane protein where the existence of the diiron carboxylate center has been shown experimentally.

Place, publisher, year, edition, pages
Stockholm: Institutionen för biokemi och biofysik, 2005. 44 p.
Keyword
electron paramagnetic resonance, diiron carboxilate proteins, ribonucleotide reductase, alternative oxidase
National Category
Biophysics
Identifiers
urn:nbn:se:su:diva-652 (URN)91-7155-131-X (ISBN)
Public defence
2005-10-07, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 13:00
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Available from: 2005-09-07 Created: 2005-09-07Bibliographically approved

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