Joint neutron crystallographic and NMR solution studies of Tyr residue ionization and hydrogen bonding: Implications for enzyme-mediated proton transfer
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- Julich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Garching (Germany)
- Technische Univ. Munchen, Garching (Germany)
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Univ. of Florida, Gainesville, FL (United States)
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Julich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Garching (Germany)
Human carbonic anhydrase II (HCA II) uses a Zn-bound OH-/H2O mechanism to catalyze the reversible hydration of CO2. This catalysis also involves a separate proton transfer step, mediated by an ordered solvent network coordinated by hydrophilic residues. One of these residues, Tyr7, was previously shown to be deprotonated in the neutron crystal structure at pH 10. This observation indicated that Tyr7 has a perturbed pKa compared with free tyrosine. To further probe the pKa) of this residue, NMR spectroscopic measurements of [13C] Tyr-labeled holo HCA II (with active-site Zn present) were preformed to titrate all Tyr residues between pH 5.4-11.0. In addition, neutron studies of apo HCA II (with Zn removed from the active site) at pH 7.5 and holo HCA II at pH 6 were conducted. This detailed interrogation of tyrosines in HCA II by NMR and neutron crystallography revealed a significantly lowered pKa of Tyr7 and how pH and Tyr proximity to Zn affect hydrogen-bonding interactions.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States); Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER)
- Grant/Contract Number:
- AC52-06NA25396; AC05-00OR22725; 20110535ER
- OSTI ID:
- 1236701
- Alternate ID(s):
- OSTI ID: 1261433
- Report Number(s):
- LA-UR-15-20968
- Journal Information:
- Proceedings of the National Academy of Sciences of the United States of America, Vol. 112, Issue 18; ISSN 0027-8424
- Publisher:
- National Academy of Sciences, Washington, DC (United States)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
Web of Science
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