Combined High-Resolution Neutron and X-ray Analysis of Inhibited Elastase Confirms the Active-Site Oxyanion Hole but Rules against a Low-Barrier Hydrogen Bond

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• 作者：Taro Tamada ; Takayoshi Kinoshita ; Kazuo Kurihara ; Motoyasu Adachi ; Takashi Ohhara ; Keisuke Imai ; Ryota Kuroki ; Toshiji Tada
• 刊名：Journal of the American Chemical Society
• 出版年：2009
• 出版时间：August 12, 2009
• 年：2009
• 卷：131
• 期：31
• 页码：11033-11040
• 全文大小：490K
• 年卷期：v.131,no.31(August 12, 2009)
• ISSN：1520-5126

文摘

To help resolve long-standing questions regarding the catalytic activity of the serine proteases, the structure of porcine pancreatic elastase has been analyzed by high-resolution neutron and X-ray crystallography. To mimic the tetrahedral transition intermediate, a peptidic inhibitor was used. A single large crystal was used to collect room-temperature neutron data to 1.65 Å resolution and X-ray data to 1.20 Å resolution. Another crystal provided a low-temperature X-ray data set to 0.94 Å resolution. The neutron data are to higher resolution than previously reported for a serine protease and the X-ray data are comparable with other studies. The neutron and X-ray data show that the hydrogen bond between His57 and Asp102 (chymotrypsin numbering) is 2.60 Å in length and that the hydrogen-bonding hydrogen is 0.80−0.96 Å from the histidine nitrogen. This is not consistent with a low-barrier hydrogen which is predicted to have the hydrogen midway between the donor and acceptor atom. The observed interaction between His57 and Asp102 is essentially a short but conventional hydrogen bond, sometimes described as a short ionic hydrogen bond. The neutron analysis also shows that the oxygen of the oxopropyl group of the inhibitor is present as an oxygen anion rather than a hydroxyl group, supporting the role of the “oxyanion hole” in stabilizing the tetrahedral intermediate in catalysis.