Critical Involvement of the E373鈥揇434 Region in the Acid Sensitivity of a NhaB-Type Na+/H+ Antiporter from Vibrio alginolyticus

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• 作者：Wakako Kiriyama ; Tatsunosuke Nakamura ; Masahiro Fukuhara ; Toshio Yamaguchi
• 刊名：Biochemistry
• 出版年：2012
• 出版时间：October 2, 2012
• 年：2012
• 卷：51
• 期：39
• 页码：7766-7774
• 全文大小：469K
• 年卷期：v.51,no.39(October 2, 2012)
• ISSN：1520-4995

文摘

It has been well established that VaNhaB, a NhaB-type Na⁺/H⁺ antiporter found in Vibrio alginolyticus, exhibits a striking acid sensitivity. However, the molecular basis of the pH-dependent regulatory mechanism of the antiport activity is yet to be investigated. In this study, we generated various chimeric proteins composed of VaNhaB and a pH insensitive ortholog found in Escherichia coli (EcNhaB) and analyzed the pH responses of their Na⁺/H⁺ antiport activities to search for the key residues or domains that are involved in the pH sensitivity of VaNhaB. Our results revealed the significant importance of a stretch of amino acid residues within the loop 8鈥搇oop 9 regions (E373鈥揇434) responsible for the acid sensitivity of VaNhaB, along with the possible involvement of other unidentified residues that are widely spread in the primary structure of VaNhaB. Moreover, we demonstrated that the E373鈥揇434 region of VaNhaB was able to confer some degree of acid sensitivity on our pH insensitive chimeric antiporter that is mainly composed of EcNhaB except for seven amino acid substitutions at the N-terminal end. This result strongly suggested the possibility that the E373鈥揇434 region is able to act, at least partially, as machinery that diminishes the activity of the NhaB-type antiporter at an acidic pH.