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Please use this identifier to cite or link to this item: http://hdl.handle.net/10119/7869

Title: Tautomerism of Histidine 64 Associated with Proton Transfer in Catalysis of Carbonic Anhydrase
Authors: Shimahara, Hideto
Yoshida, Takuya
Shibata, Yasutaka
Shimizu, Masato
Kyogoku, Yoshimasa
Sakiyama, Fumio
Nakazawa, Takashi
Tate, Shin-ichi
Ohki, Shin-ya
Kato, Takeshi; Moriyama, Hozumi; Kishida, Ken-ichi; Tano, Yasuo; Ohkubo, Tadayasu; Kobayashi, Yuji
Issue Date: 2007-3-30
Publisher: American Society for Biochemistry and Molecular Biology
Magazine name: Journal of Biological Chemistry
Volume: 282
Number: 13
Start page: 9646
End page: 9656
DOI: 10.1074/jbc.M609679200
Abstract: 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.
Rights: Copyright (C) 2007 American Society for Biochemistry and Molecular Biology. Hideto Shimahara, Takuya Yoshida, Yasutaka Shibata, Masato Shimizu, Yoshimasa Kyogoku, Fumio Sakiyama, Takashi Nakazawa, Shin-ichi Tate, Shin-ya Ohki, Takeshi Kato, Hozumi Moriyama, Ken-ichi Kishida, Yasuo Tano, Tadayasu Ohkubo, and Yuji Kobayashi, Journal of Biological Chemistry, 282(13), 2007, 9646-9656.
URI: http://hdl.handle.net/10119/7869
Material Type: publisher
Appears in Collections:g10-1. 雑誌掲載論文 (Journal Articles)

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