Open AccessHigh thermal and chemical stability of Thermus thermophilus seven‐iron ferredoxin
Author(s) -
Griffin Susanne,
Higgins Catherine L.,
Soulimane Tewfik,
WittungStafshede Pernilla
Publication year - 2003
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1033.2003.03873.x
Subject(s) - thermus thermophilus , ferredoxin , guanidine , chemistry , crystallography , chemical stability , thermal stability , valence (chemistry) , sulfur , inorganic chemistry , organic chemistry , biochemistry , enzyme , escherichia coli , gene
To probe the stability of the seven‐iron ferredoxin from Thermus thermophilus (FdTt), we investigated its chemical and thermal denaturation processes in solution. As predicted from the crystal structure, FdTt is extremely resistant to perturbation. The guanidine hydrochloride‐induced unfolding transition shows a midpoint at 6.5 m (pH 7, 20 °C), and the thermal midpoint is above boiling, at 114 °C. The stability of FdTt is much lower at acidic pH, suggesting that electrostatic interactions are important for the high stability at higher pH. On FdTt unfolding at alkaline pH, new absorption bands at 520 nm and 610 nm appear transiently, resulting from rearrangement of the cubic clusters into linear three‐iron species. A range of iron–sulfur proteins has been found to accommodate these novel clusters in vitro , although no biological function has yet been assigned.