Cooperative protein–solvent tuning of proton transfer energetics: carbonic anhydrase as a case study

2020 ◽  
Vol 22 (35) ◽  
pp. 19975-19981
Author(s):  
Laura Zanetti-Polzi ◽  
Massimiliano Aschi ◽  
Isabella Daidone
Keyword(s):  
Carbonic Anhydrase ◽  
Water Molecule ◽  
Proton Transfer ◽  
Active Site ◽  
Point Mutations ◽  
Transfer Energetics

Point mutations induce the active site dehydration and the formation of bridges of only one water molecule that efficiently transfers protons.

scholarly journals Effect of Active-site Mutation at Asn67 on the Proton Transfer Mechanism of Human Carbonic Anhydrase II

Biochemistry ◽  
2009 ◽  
Vol 48 (33) ◽  
pp. 7996-8005 ◽  
Author(s):  
C. Mark Maupin ◽  
Jiayin Zheng ◽  
Chingkuang Tu ◽  
Robert McKenna ◽  
David N. Silverman ◽  
...  
Keyword(s):  
Carbonic Anhydrase ◽  
Proton Transfer ◽  
Active Site ◽  
Transfer Mechanism ◽  
Carbonic Anhydrase Ii ◽  
Site Mutation ◽  
Human Carbonic Anhydrase

Proton transfer within the active-site cavity of carbonic anhydrase III

2002 ◽  
Vol 1599 (1-2) ◽  
pp. 21-27 ◽  
Author(s):  
Haiqian An ◽  
Chingkuang Tu ◽  
Ke Ren ◽  
Philip J. Laipis ◽  
David N. Silverman
Keyword(s):  
Carbonic Anhydrase ◽  
Proton Transfer ◽  
Active Site ◽  
Carbonic Anhydrase Iii ◽  
Active Site Cavity

Intermolecular proton transfer in catalysis by carbonic anhydrase V

1999 ◽  
Vol 77 (5-6) ◽  
pp. 726-732 ◽  
Author(s):  
J Nicole Earnhardt ◽  
Chingkuang Tu ◽  
David N Silverman
Keyword(s):  
Carbonic Anhydrase ◽  
Proton Transfer ◽  
Active Site ◽  
Rate Constants ◽  
Intramolecular Proton Transfer ◽  
Proton Donor ◽  
Marcus Theory ◽  
Intermolecular Proton Transfer ◽  
Donor And Acceptor ◽  
Active Site Cavity

The dehydration of bicarbonate catalyzed by carbonic anhydrase is accompanied by the transfer of a proton from solution to the zinc-bound hydroxide. We have investigated the properties of proton transfer from donors in solution, mostly derivatives of imidazole and pyridine, to a truncated mutant of carbonic anhydrase V with replacements that render the active site cavity less sterically constrained, Tyr 64 →> Ala and Phe 65 →> Ala. Catalysis was measured by determining the rate of exchange of 18O between the CO2-HCO3- system and water, and rate constants for proton transfer were estimated as the rate-limiting step in the release of H218O from the enzyme to solution. Each proton donor enhanced catalytic activity in a saturable manner. The resulting rate constants for proton transfer when compared with the values of pKa of the donor and acceptor gave a Brønsted plot of high curvature. These data could also be described by Marcus theory which showed an intrinsic barrier for intermolecular proton transfer near 0.8 kcal/mol and a work term or thermodynamic contribution to the free energy of reaction near 10 kcal/mol. This low intrinsic kinetic barrier for proton transfer is very similar to nonenzymic bimolecular proton transfer between nitrogen and oxygen acids and bases in solution. However, the significant thermodynamic contribution suggests appreciable involvement of solvent and active-site organization prior to proton transfer. These Marcus parameters are very similar to those describing intramolecular proton transfer from His 64 in carbonic anhydrase, suggesting similarities in the intra- and intermolecular proton transfer processes.Key words: carbonic anhydrase, proton transfer, Marcus theory, carbon dioxide.

scholarly journals Active-site solvent replenishment observed during human carbonic anhydrase II catalysis

IUCrJ ◽  
2018 ◽  
Vol 5 (1) ◽  
pp. 93-102 ◽  
Author(s):  
Jin Kyun Kim ◽  
Carrie L. Lomelino ◽  
Balendu Sankara Avvaru ◽  
Brian P. Mahon ◽  
Robert McKenna ◽  
...  
Keyword(s):  
Carbonic Anhydrase ◽  
Proton Transfer ◽  
Active Site ◽  
Water Reservoir ◽  
Bound Water ◽  
Nucleophilic Attack ◽  
Carbonic Anhydrase Ii ◽  
Intermediate Water ◽  
Water Network ◽  
Human Carbonic Anhydrase

Human carbonic anhydrase II (hCA II) is a zinc metalloenzyme that catalyzes the reversible hydration/dehydration of CO2/HCO3 −. Although hCA II has been extensively studied to investigate the proton-transfer process that occurs in the active site, its underlying mechanism is still not fully understood. Here, ultrahigh-resolution crystallographic structures of hCA II cryocooled under CO2 pressures of 7.0 and 2.5 atm are presented. The structures reveal new intermediate solvent states of hCA II that provide crystallographic snapshots during the restoration of the proton-transfer water network in the active site. Specifically, a new intermediate water (WI′) is observed next to the previously observed intermediate water WI, and they are both stabilized by the five water molecules at the entrance to the active site (the entrance conduit). Based on these structures, a water network-restructuring mechanism is proposed, which takes place at the active site after the nucleophilic attack of OH− on CO2. This mechanism explains how the zinc-bound water (WZn) and W1 are replenished, which are directly responsible for the reconnection of the His64-mediated proton-transfer water network. This study provides the first `physical' glimpse of how a water reservoir flows into the hCA II active site during its catalytic activity.

scholarly journals Proton transfer between hemoglobin and the carbonic anhydrase active site.

1978 ◽  
Vol 253 (8) ◽  
pp. 2563-2567
Author(s):  
D.N. Silverman ◽  
C. Tu ◽  
G.C. Wynns
Keyword(s):  
Carbonic Anhydrase ◽  
Proton Transfer ◽  
Active Site
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