Energetics of Coiled Coil Folding: The Nature of the Transition States

详细信息    查看全文

• 作者：Hans Rudolf Bosshard ; Eberhard Dü ; rr ; Thomas Hitz ; and Ilian Jelesarov
• 刊名：Biochemistry
• 出版年：2001
• 出版时间：March 27, 2001
• 年：2001
• 卷：40
• 期：12
• 页码：3544 - 3552
• 全文大小：98K
• 年卷期：v.40,no.12(March 27, 2001)
• ISSN：1520-4995

文摘

Coiled coils are simple models for studying the association of two polypeptide chains to forma folded protein. Previous work has shown that the folding of a coiled coil can be described by a two-state transition between two unfolded monomeric peptide chains and a folded coiled coil dimer. Here wereport the thermodynamic activation parameters for the folding and unfolding of two unrelated coiledcoils: C62GCN4 and A₂. C62GCN4 corresponds to the 62 C-terminal residues of yeast transcriptionfactor GCN4. The peptide forms a dimeric coiled coil through its 33 C-terminal residues. A₂ is a designed30-residue dimeric coiled coil whose folding is induced by low pH [Dürr, E., Jelesarov, I., and Bosshard,H. R. (1999) Biochemistry 38, 870-880]. Folding and unfolding were assessed under identical nativebuffer conditions so that the microscopic reversibility applied and the transition state was the same forfolding and unfolding. The time course of folding was followed from the self-quenching of a C-terminalfluorescent label (Texas Red). The overall folding of both peptides is enthalpy-driven and opposed by aloss of entropy. The main energetic changes occur after the system has passed the transition state. In thefolding of C62GCN4, only 10-20% of the heat capacity change is attained between the monomeric stateand the dimeric transition state. For coiled coil A₂, the fractional heat capacity change preceding thetransition state is 30-40%. The results indicate that the activated states of folding of coiled coils are notwell structured and differ considerably from the folded coiled coil conformation. These findings are inagreement with a rate-limiting transition state in which the coiled coil helices and the hydrophobic coiledcoil interface are poorly developed.