Interaction between Na+ Ion and Carboxylates of the PomA−PomB Stator Unit Studied by ATR-FTIR Spectroscopy

详细信息    查看全文

• 作者：Yuki Sudo ; Yuya Kitade ; Yuji Furutani ; Masaru Kojima ; Seiji Kojima ; Michio Homma ; Hideki Kandori
• 刊名：Biochemistry
• 出版年：2009
• 出版时间：December 15, 2009
• 年：2009
• 卷：48
• 期：49
• 页码：11699-11705
• 全文大小：907K
• 年卷期：v.48,no.49(December 15, 2009)
• ISSN：1520-4995

文摘

Bacterial flagellar motors are molecular machines powered by the electrochemical potential gradient of specific ions across the membrane. The PomA−PomB stator complex of Vibrio alginolyticus couples Na⁺ influx to torque generation in this supramolecular motor, but little is known about how Na⁺ associates with the PomA−PomB complex in the energy conversion process. Here, by means of attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy, we directly observed binding of Na⁺ to carboxylates in the PomA−PomB complex, including the functionally essential residue Asp24. The Na⁺ affinity of Asp24 is estimated to be 85 mM, close to the apparent K_m value from the swimming motility of the cells (78 mM). At least two other carboxylates are shown to be capable of interacting with Na⁺, but with somewhat lower affinities. We conclude that Asp24 and at least two other carboxylates constitute Na⁺ interaction sites in the PomA−PomB complex. This work reveals features of the Na⁺ pathway in the PomA−PomB Na⁺ channel by using vibrational spectroscopy.