Structural and Dynamic Characterization of the Acid-Unfolded State of hUBF HMG Box 1 Provides Clues for the Early Events in Protein Folding

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• 作者：Xuecheng Zhang ; Yingqi Xu ; Jiahai Zhang ; Jihui Wu ; and Yunyu Shi
• 刊名：Biochemistry
• 出版年：2005
• 出版时间：June 7, 2005
• 年：2005
• 卷：44
• 期：22
• 页码：8117 - 8125
• 全文大小：162K
• 年卷期：v.44,no.22(June 7, 2005)
• ISSN：1520-4995

文摘

To understand the events that occur in the early stages of the folding of hUBF HMG box 1,we characterized its pH 2.1 unfolded state in detail with NMR. Through a triple resonance strategy, theassignments of complete backbone and some side chains were achieved. Then, significant conformationalinformation was extracted from secondary chemical shifts, interresidual ¹H-¹H NOEs, ³J_HNHA couplingconstants, amide proton temperature coefficients, and ¹⁵N relaxation data. The secondary chemical shiftsfor ¹³CA, ¹³CB, ¹³CO, ¹HA, and ¹HN indicate that the residues between 64 and 78 exhibit a substantialpreference for helical structure in the acid-unfolded state, which is also evidenced by the relatively morenegative deviations of ³J_HNHA and amide proton temperature coefficients from their corresponding random-coil values and particularly confirmed by the strongest sequential d_NN(i, i + 1) proton NOEs along theregion. Following this region until residue 82 is a segment that tends to form a turn-like structure, whichis unstable and exchanges between alternative states. In addition, some evidences imply that the regions18-28 and 38-43 also possess propensities for helical structure but to a different less degree than theregion 64-78. The polypeptide backbone dynamics investigated using reduced spectral density functionshows apparent motional restrictions in residual structural regions and to less extent at some hydrophobicresidues. On the basis of the results presented herein, we propose a potential protein-folding pathway onwhich these residual structures play a role of initiation site in the early folding stages.