title: Equilibrium unfolding of a small low-potential cytochrome, cytochrome c553 from Desulfovibrio vulgaris.
abstract: To understand general aspects of stability and folding of c-type cytochromes, we have studied the folding characteristics of cytochrome c553 from Desulfovibrio vulgaris (Hildenborough). This cytochrome is structurally similar but lacks sequence homology to other heme proteins; moreover, it has an abnormally low reduction potential. Unfolding of oxidized and reduced cytochrome c553 by guanidine hydrochloride (GuHCl) was monitored by circular dichroism (CD) and Soret absorption; the same unfolding curves were obtained with both methods supporting that cytochrome c553 unfolds by an apparent two-state process. Reduced cytochrome c553 is 7(3) kJ/mol more stable than the oxidized form; accordingly, the reduction potential of unfolded cytochrome c553 is 100(20) mV more negative than that of the folded protein. In contrast to many other unfolded cytochrome c proteins, upon unfolding at pH 7.0 both oxidized and reduced heme in cytochrome c553 become high-spin. The lack of heme misligation in unfolded cytochrome c553 implies that its unfolded structure is less constrained than those of cytochromes c with low-spin, misligated hemes.
authors.affiliation: Chemistry Department, Tulane University, New Orleans, Louisiana 70118-5698, USA. pernilla@mailhost.tcs.tulane.edu
authors.forename: P
authors.initials: P
authors.lastname: Wittung-Stafshede
mesh_terms: D002942:Circular Dichroism; D003574:Cytochrome c Group / Q000737:chemistry*; D016969:Desulfovibrio vulgaris / Q000201:enzymology*; D006418:Heme / Q000737:chemistry; D010084:Oxidation-Reduction; D011489:Protein Denaturation; D013816:Thermodynamics
chemical_list: D003574:Cytochrome c Group; C083951:cytochrome c553; D006418:Heme