tailieunhanh - Báo cáo khoa học: High thermal and chemical stability of Thermus thermophilus seven-iron ferredoxin Linear clusters form at high pH on polypeptide unfolding

To probe the stability of the seven-iron ferredoxin from Thermus thermophilus(FdTt), we investigated its chemical and thermal denaturationprocesses from the crystal structure, FdTt is extremely resistant to perturbation. The guanidine hydrochloride-induced unfolding transition shows a midpoint at (pH 7, 20 C), andthe thermalmidpoint is aboveboiling, 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 tran-siently, resulting from rearrangement of the cubic clusters into linear three-iron species | Eur. J. Biochem. 270 4736-4743 2003 FEBS 2003 doi High thermal and chemical stability of Thermus thermophilus seven-iron ferredoxin Linear clusters form at high pH on polypeptide unfolding Susanne Griffin1 Catherine L. Higgins1 Tewfik Soulimane2 and Pernilla Wittung-Stafshede1 1 Department of Chemistry Tulane University New Orleans LA USA 2Paul Scherrer Institute Structural Biology Villigen Switzerland 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 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 Ton-su 1I ur protei ns has been found to accommodate these novel clusters in vitro although no biological function has yet been assigned. Keywords ferredoxin linear iron-sulfur cluster protein unfolding thermostability Thermus thermophilus. Many proteins require the binding of cofactors to perform their biological activity. It has been demonstrated in vitro that many proteins retain interactions with their cofactors after polypeptide unfolding 1-6 . Therefore it is possible that cofactors bind to their corresponding polypeptides before or during folding in vivo. Cofactors most often stabilize the native states of the proteins with which they interact 1-6 . However the manner in which cofactors affect polypeptide folding and unfolding pathways remains poorly understood. Iron-sulfur Fe-S clusters represent one of nature s .

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