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Paramagnetic states of diiron carboxylate proteins
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
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 [en]
electron paramagnetic resonance, diiron carboxilate proteins, ribonucleotide reductase, alternative oxidase
National Category
Biophysics
Identifiers
URN: urn:nbn:se:su:diva-652ISBN: 91-7155-131-X (print)OAI: oai:DiVA.org:su-652DiVA: diva2:196604
Public defence
2005-10-07, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 13:00
Opponent
Supervisors
Available from: 2005-09-07 Created: 2005-09-07Bibliographically approved
List of papers
1. The Radical Site in Chlamydial Ribonucleotide Reductase Defines a New R2 Subclass
Open this publication in new window or tab >>The Radical Site in Chlamydial Ribonucleotide Reductase Defines a New R2 Subclass
Show others...
2004 In: Science, ISSN 0036-8075, Vol. 305, no 5681, 245-248 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24050 (URN)
Note
Part of urn:nbn:se:su:diva-652Available from: 2005-09-07 Created: 2005-09-07Bibliographically approved
2. A stable FeIII-FeIV replacement of tyrosyl radical in a class I ribonucleotide reductase
Open this publication in new window or tab >>A stable FeIII-FeIV replacement of tyrosyl radical in a class I ribonucleotide reductase
2005 In: Biochemical and Biophysical Research Communications, ISSN 0006-291X, Vol. 330, no 4, 1213-1216 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24051 (URN)
Note
Part of urn:nbn:se:su:diva-652Available from: 2005-09-07 Created: 2005-09-07Bibliographically approved
3. Characterization of the active state of chlamidial ribonucleotide reductase: tyrosyl radical functions replaced by FeIII-FeIV cluster
Open this publication in new window or tab >>Characterization of the active state of chlamidial ribonucleotide reductase: tyrosyl radical functions replaced by FeIII-FeIV cluster
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-24052 (URN)
Note
Part of urn:nbn:se:su:diva-652Available from: 2005-09-07 Created: 2005-09-07 Last updated: 2010-01-13Bibliographically approved
4. EPR and 57Fe-ENDOR characterisation of the high-valent diiron species X in ribonucleotide reductase protein R2 of Chlamydia trachomatis
Open this publication in new window or tab >>EPR and 57Fe-ENDOR characterisation of the high-valent diiron species X in ribonucleotide reductase protein R2 of Chlamydia trachomatis
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Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-24053 (URN)
Note
Part of urn:nbn:se:su:diva-652Available from: 2005-09-07 Created: 2005-09-07 Last updated: 2010-01-13Bibliographically approved
5. EPR Studies of the Mitochondrial Alternative Oxidase. Evidence for a Diiron Carboxylate Center
Open this publication in new window or tab >>EPR Studies of the Mitochondrial Alternative Oxidase. Evidence for a Diiron Carboxylate Center
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2002 In: Journal of Biological Chemistry, ISSN 0021-9258, Vol. 277, no 46, 43608-43614 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-24054 (URN)
Note
Part of urn:nbn:se:su:diva-652Available from: 2005-09-07 Created: 2005-09-07Bibliographically approved

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