Probing the Acid-Induced Packing Structure Changes of the Molten Globule Domains of a Protein near Equilibrium Unfolding

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• 作者：Yi-Qi YehKuei-Fen Liao ; Orion Shih ; Ying-Jen Shiu ; Wei-Ru Wu ; Chun-Jen Su ; Po-Chang Lin ; U-Ser Jeng
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2017
• 出版时间：January 19, 2017
• 年：2017
• 卷：8
• 期：2
• 页码：470-477
• 全文大小：562K
• ISSN：1948-7185

文摘

Using simultaneously scanning small-angle X-ray scattering (SAXS) and UV–vis absorption with integrated online size exclusion chromatography, supplemental with molecular dynamics simulations, we unveil the long-postulated global structure evolution of a model multidomain protein bovine serum albumin (BSA) during acid-induced unfolding. Our results differentiate three global packing structures of the three molten globule domains of BSA, forming three intermediates I₁, I₂, and E along the unfolding pathway. The I₁–I₂ transition, overlooked in all previous studies, involves mainly coordinated reorientations across interconnected molten globule subdomains, and the transition activates a critical pivot domain opening of the protein for entering into the E form, with an unexpectedly large unfolding free energy change of −9.5 kcal mol^–1, extracted based on the observed packing structural changes. The revealed local packing flexibility and rigidity of the molten globule domains in the E form elucidate how collective motions of the molten globule domains profoundly influence the folding–unfolding pathway of a multidomain protein.