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Equilibrium unfolding of a small low‐potential cytochrome, cytochrome c 553 from Desulfovibrio vulgaris
Author(s) -
WittungStafshede Pernilla
Publication year - 1999
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.8.7.1523
Subject(s) - desulfovibrio vulgaris , cytochrome , heme , chemistry , cytochrome c , desulfovibrio , cytochrome c peroxidase , stereochemistry , cytochrome b , circular dichroism , cytochrome p450 reductase , equilibrium unfolding , crystallography , coenzyme q – cytochrome c reductase , biochemistry , biology , organic chemistry , bacteria , genetics , sulfate , gene , mitochondrion , mitochondrial dna , enzyme
To understand general aspects of stability and folding of c ‐type cytochromes, we have studied the folding characteristics of cytochrome c 553 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 c 553 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 c 553 unfolds by an apparent two‐state process. Reduced cytochrome c 553 is 7(3) kJ/mol more stable than the oxidized form; accordingly, the reduction potential of unfolded cytochrome c 553 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 c 553 become high‐spin. The lack of heme misligation in unfolded cytochrome c 553 implies that its unfolded structure is less constrained than those of cytochromes c with low‐spin, misligated hemes.