Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 111, Issue 52, Pages 18454-18459Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1417923111
Keywords
enzyme; hydrogen bonding; nuclear quantum effects; proton delocalization; ab initio path integral molecular dynamics
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Funding
- Stanford Center for Molecular Analysis and Design
- National Science Foundation (NSF) Predoctoral Fellowship Program
- Stanford Bio-X Interdisciplinary Graduate Fellowship
- Terman Fellowship
- Alfred P. Sloan Research Fellowship
- Hellman Faculty Scholar Fund Fellowship
- Stanford University startup funds
- National Institutes of Health [GM27738]
- NSF [ACI-1053575, TG-CHE140013]
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Enzymes use protein architectures to create highly specialized structural motifs that can greatly enhance the rates of complex chemical transformations. Here, we use experiments, combined with ab initio simulations that exactly include nuclear quantum effects, to show that a triad of strongly hydrogen-bonded tyrosine residues within the active site of the enzyme ketosteroid isomerase (KSI) facilitates quantum proton delocalization. This delocalization dramatically stabilizes the deprotonation of an active-site tyrosine residue, resulting in a very large isotope effect on its acidity. When an intermediate analog is docked, it is incorporated into the hydrogen-bond network, giving rise to extended quantum proton delocalization in the active site. These results shed light on the role of nuclear quantum effects in the hydrogen-bond network that stabilizes the reactive intermediate of KSI, and the behavior of protons in biological systems containing strong hydrogen bonds.
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