On the Stability of a Single-Turn -Helix: The Single versus Multiconformation Problem

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• 作者：James P. Snyder ; Ami S. Lakdawala ; and Michael J. Kelso
• 刊名：Journal of the American Chemical Society
• 出版年：2003
• 出版时间：January 22, 2003
• 年：2003
• 卷：125
• 期：3
• 页码：632 - 633
• 全文大小：84K
• 年卷期：v.125,no.3(January 22, 2003)
• ISSN：1520-5126

文摘

The pentapeptide Ac-HAAAH-NH<SUB>2, cyclized through its imidazoles by Pd^II to give [Pd(en)(peptide)]²⁺, has recently been evaluated by 2-D NMR and simulated annealing as a single s/gifchars/alpha.gif" BORDER=0>-helix conformation in solution. In the present work, we have questioned this assumption by developing Pd²⁺ parameters for AMBER*, performing an extensive conformational search for the [Pd(en)(peptide)]²⁺, and deconvoluting the averaged NMR data into eight rapidly equilibrating conformations with populations ranging from 2 to 55%. None of the latter correspond to the s/gifchars/alpha.gif" BORDER=0>-helix, although a 3% form possesses a related structure. As a critical component of interpreting an averaged NMR spectrum in terms of a single conformation, we advise testing this assumption with a method that permits conformational deconvolution.