title: Role of the tertiary and quaternary structures in the stability of dimeric copper, zinc superoxide dismutases.
abstract: The equilibrium unfolding process of human Cu,Zn superoxide dismutase has been quantitatively monitored through circular dichroism and fluorescence spectroscopy as a function of increasing guanidinium hydrochloride concentration. The process occurs through the formation of a monomeric intermediate species following a three-state transition equilibrium. Comparison with the stability of the prokaryotic Cu,Zn SOD from P. leiognathi shows that the eukaryotic enzyme is more stable than the prokaryotic enzyme by approximately 3 kcal/mol. This difference is due to the monomer-to-unfolded equilibrium, while the dimer-to-monomer equilibrium is comparable for the two enzymes despite their different intersubunit interactions. These results are confirmed by the unfolding of the copper-depleted derivatives. The Cu,Zn superoxide dismutase represents a good example of how evolution has found two independent quaternary assemblies maintaining the same dimer stability.
authors.affiliation: INFM and Department of Biology, University of Rome Tor Vergata, Italy.
authors.forename: M E
authors.initials: ME
authors.lastname: Stroppolo
authors.forename: F
authors.initials: F
authors.lastname: Malvezzi-Campeggi
authors.forename: G
authors.initials: G
authors.lastname: Mei
authors.forename: N
authors.initials: N
authors.lastname: Rosato
authors.forename: A
authors.initials: A
authors.lastname: Desideri
mesh_terms: D002942:Circular Dichroism; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007700:Kinetics; D010776:Photobacterium / Q000201:enzymology; D017510:Protein Folding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence; D013482:Superoxide Dismutase / Q000737:chemistry*; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry
chemical_list: D014364:Tryptophan; D013482:Superoxide Dismutase