Human carbonic anhydrase II catalyzes the reversible reaction of carbon dioxide and water to form bicarbonate and a proton. His64-mediated proton shuttling between the active site and the bulk solvent is rate limiting. Here we investigate the protonation behavior of His64 as well as its structural and dynamic features in a pH dependent way. We derive two pK values for His64, 6.25 and 7.60, that we were able to assign to its inward and outward conformation. Furthermore, we show that His64 exists in both conformations equally, independent of pH. Both conformations display an equal distribution of their two neutral tautomeric states. The life time of each conformation is short and both states display high flexibility within their orientation. Therefore, His64 is never static, but rather poised to change conformation. These findings support an energetic, dynamic and solution ensemble-based framework for the high enzymatic activity of human carbonic anhydrase II.
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http://dx.doi.org/10.1007/s00018-023-04936-z | DOI Listing |
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Graduate Program in Biochemistry and Molecular Biology, Center of Biosciences, Federal University of Rio Grande do Norte-UFRN, Av. Sen. Salgado Filho, 3000, Natal 59078-900, Brazil.
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College of Bioresources Chemical and Materials Engineering, Shaanxi University of Science & Technology, Xi'an 710021, China; Institute of Biomass & Functional Materials, Shaanxi University of Science & Technology, Xi'an 710021, China; Sustainable Functional Biomaterials Lab, Department of Wood Science, University of British Columbia, Vancouver V6T 1Z4, Canada. Electronic address:
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