title: Reconstitution of the 2Fe-2S center and g = 1.89 electron paramagnetic resonance signal into overproduced Nostoc sp. PCC 7906 Rieske protein.
abstract: The Rieske 2Fe-2S protein is a distinguishing subunit of the photosynthetic electron transport cytochrome b6f complex in chloroplast and cyanobacterial thylakoid membranes. We have constructed plasmids for overproduction in Escherichia coli of fusion, full-length, and truncated forms of the Rieske (PetC) protein from the cyanobacterium Nostoc sp. PCC 7906. A glutathione S-transferase/Rieske fusion protein was used to prepare specific chicken egg-yolk antibodies against the Rieske protein. Expression of the nonfusion petC gene in a T7 RNA polymerase promoter vector produced copious quantities of the full-length Rieske protein predominantly as inclusion bodies. The highly enriched, Rieske protein from inclusion bodies has been denatured in guanidine hydrochloride and refolded and the characteristic 2Fe-2S cluster reconstituted in vitro by incubation with iron and sulfide under reducing conditions. Purification by chromatography on Whatman DE52 cellulose and ultrafiltration through a 30000 molecular weight cutoff membrane yielded pure and predominantly monomeric Rieske protein. Reconstituted Rieske preparations showed intense and highly characteristic gx = 1.74, gy = 1.89, and gz = 2.03 "Rieske-type" electron paramagnetic resonance signals at 15 K. Two methods of reconstitution yielded Rieske preparations in which 20-60% of the protein contained 2Fe-2S clusters as determined by EPR spin quantitation. The reconstituted Rieske protein was soluble and stable at 4 degrees C in buffers containing nonionic detergents and showed a redox midpoint potential of +321 mV at pH 7.0 as determined by optical circular dichroism (CD) spectroscopy. These data demonstrate the in vitro restoration of a Cys and His liganded 2Fe-2S cluster and provide the basis for mutational and structural analysis of a PetC Rieske protein of oxygenic photosynthesis.
authors.affiliation: Department of Biology and Microbiology, University of Wisconsin, Oshkosh 54901, USA.
authors.forename: B
authors.initials: B
authors.lastname: Holton
authors.forename: X
authors.initials: X
authors.lastname: Wu
authors.forename: A I
authors.initials: AI
authors.lastname: Tsapin
authors.forename: D M
authors.initials: DM
authors.lastname: Kramer
authors.forename: R
authors.initials: R
authors.lastname: Malkin
authors.forename: T
authors.initials: T
authors.lastname: Kallas
mesh_terms: D000818:Animals; D002645:Chickens; D000458:Cyanobacteria / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D014450:Electron Transport Complex III; D006863:Hydrogen-Ion Concentration; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D008970:Molecular Weight; D010957:Plasmids; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D014462:Ultrafiltration
chemical_list: D007506:Iron-Sulfur Proteins; D011993:Recombinant Fusion Proteins; C037989:Rieske iron-sulfur protein; D014450:Electron Transport Complex III