π-Interaction Tuning of the Active Site Properties of Metalloproteins

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• 作者：Sachiko Yanagisawa ; Peter B. Crowley ; Susan J. Firbank ; Anne T. Lawler ; David M. Hunter ; William McFarlane ; Chan Li ; Takamitsu Kohzuma ; Mark J. Banfield ; Christopher Dennison
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：November 19, 2008
• 年：2008
• 卷：130
• 期：46
• 页码：15420-15428
• 全文大小：344K
• 年卷期：v.130,no.46(November 19, 2008)
• ISSN：1520-5126

文摘

The influence of π-interactions with a His ligand have been investigated in a family of copper-containing redox metalloproteins. The Met16Phe and Met16Trp pseudoazurin, and Leu12Phe spinach and Leu14Phe Phormidium laminosum plastocyanin variants possess active-site π-contacts between the introduced residue and His81 and His87/92 respectively. The striking overlap of the side chain of Phe16 in the Met16Phe variant and that of Met16 in wild type pseudoazurin identifies that this position provides an important second coordination sphere interaction in both cases. His-ligand protonation and dissociation from Cu(I) occurs in the wild type proteins resulting in diminished redox activity, providing a [H⁺]-driven switch for regulating electron transfer. The introduced π-interaction has opposing effects on the pK_a for the His ligand in pseudoazurin and plastocyanin due to subtle differences in the π-contact, stabilizing the coordinated form of pseudoazurin whereas in plastocyanin protonation and dissociation is favored. Replacement of Pro36, a residue that has been suggested to facilitate structural changes upon His ligand protonation, with a Gly, has little effect on the pK_a of His87 in spinach plastocyanin. The mutations at Met16 have a significant influence on the reduction potential of pseudoazurin. Electron self-exchange is enhanced, whereas association with the physiological partner, nitrite reductase, is only affected by the Met16Phe mutation, but k_cat is halved in both the Met16Phe and Met16Trp variants. Protonation of the His ligand is the feature most affected by the introduction of a π-interaction.