Quantitative dissection of hydrogen bond-mediated proton transfer in the ketosteroid isomerase active site

Paul A. Sigala, Aaron T. Fafarman, Jason P. Schwans, Stephen D. Fried, Timothy D. Fenn, Jose M.M. Caaveiro, Brandon Pybus, Dagmar Ringe, Gregory A. Petsko, Steven G. Boxer, Daniel Herschlag

研究成果: ジャーナルへの寄稿学術誌査読

35 被引用数 (Scopus)

抄録

Hydrogen bond networks are key elements of protein structure and function but have been challenging to study within the complex protein environment. We have carried out in-depth interrogations of the proton transfer equilibriumwithin a hydrogen bond network formed to bound phenols in the active site of ketosteroid isomerase. We systematically varied the proton affinity of the phenol using differing electron-withdrawing substituents and incorporated site-specific NMR and IR probes to quantitatively map the proton and charge rearrangements within the network that accompany incremental increases in phenol proton affinity. The observed ionization changes were accurately described by a simple equilibrium proton transfer model that strongly suggests the intrinsic proton affinity of one of the Tyr residues in the network, Tyr16, does not remain constant but rather systematically increases due to weakening of the phenol-Tyr16 anion hydrogen bond with increasing phenol proton affinity. Using vibrational Stark spectroscopy, we quantified the electrostatic field changes within the surrounding active site that accompany these rearrangements within the network. We were able to model these changes accurately using continuum electrostatic calculations, suggesting a high degree of conformational restriction within the protein matrix. Our study affords direct insight into the physical and energetic properties of a hydrogen bond network within a protein interior and provides an example of a highly controlled systemwith minimal conformational rearrangements in which the observed physical changes can be accurately modeled by theoretical calculations.

本文言語英語
ページ(範囲)E2552-E2561
ジャーナルProceedings of the National Academy of Sciences of the United States of America
110
28
DOI
出版ステータス出版済み - 7月 9 2013
外部発表はい

!!!All Science Journal Classification (ASJC) codes

  • 一般

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