Tautomerism of Histidine 64 Associated with Proton Transfer in Catalysis of Carbonic Anhydrase
スポンサーリンク
概要
- 論文の詳細を見る
The imidazole ^<15>N signals of histidine 64 (His^<64>), involved in the catalytic function of human carbonic anhydrase II (hCAII), were assigned unambiguously. This was accomplished by incorporating the labeled histidine as probes for solution NMR analysis, with ^<15>N at ring-N <δ1> and N^<∈2>, ^<13>C at ring-C∈1, ^<13>C and ^<15>N at all carbon and nitrogen, or ^<15>N at the amide nitrogen and the labeled glycine with ^<13>C at the carbonyl carbon. Using the pH dependence of ring-^<15>N signals and a comparison between experimental and simulated curves, we determined that the tautomeric equilibrium constant (K_T) of His^<64> is 1.0, which differs from that of other histidine residues. This unique value characterizes the imidazole nitrogen atoms of His^<64> as both a general acid (a) and base (b): its ∈2-nitrogen as (a) releases one proton into the bulk, whereas itsδ1-nitrogen as (b) extracts another proton from a water molecule within the water bridge coupling to the zinc-bound water inside the cave. This accelerates the generation of zinc-bound hydroxide to react with the carbon dioxide. Releasing the productive bicarbonate ion from the inside separates the water bridge pathway, in which the next water molecules move into beside zinc ion. A new water molecule is supplied from the bulk to near the δ1-nitrogen of His^<64>. These reconstitute the water bridge. Based on these features, we suggest here a catalytic mechanism for hCAII: the tautomerization of His^<64> can mediate the transfers of both protons and water molecules at a neutral pH with high efficiency, requiring no time- or energy-consuming processes.
- American Society for Biochemistry and Molecular Biologyの論文
- 2007-03-30
American Society for Biochemistry and Molecular Biology | 論文
- Functions of chondroitin sulfate/dermatan sulfate chains in brain development: Critical roles of E and iE disaccharide units recognized by a single chain antibody GD3G7.
- Interaction between the N-terminal and middle regions is essential for the in vivo function of HSP90 molecular chaperone.
- Four-electron reduction of dioxygen by a multicopper oxidase, CueO, and roles of Asp112 and Glu506 located adjacent to the trinuclear copper center
- Intracellular Trafficking Pathway of Yeast Long-chain Base Kinase Lcb4, from Its Synthesis to Its Degradation
- Regulation of the transport and protein levels of the inositol phosphorylceramide mannosyltransferases Csg1 and Csh1 by the Ca2+ binding protein Csg2