Herrmann L, Schwan D, Garner R, Mobley H L, Haas R, Schäfer K P, Melchers K
Department of Molecular Biology, Byk Gulden Pharmaceuticals, D-78462 Konstanz, Germany.
Mol Microbiol. 1999 Aug;33(3):524-36. doi: 10.1046/j.1365-2958.1999.01496.x.
Inactivation of Helicobacter pylori cadA, encoding a putative transition metal ATPase, was only possible in one of four natural competent H. pylori strains, designated 69A. All tested cadA mutants showed increased growth sensitivity to Cd(II) and Zn(II). In addition, some of them showed both reduced 63Ni accumulation during growth and no or impaired urease activity, which was not due to lack of urease enzyme subunits. Gene complementation experiments with plasmid (pY178)-derived H. pylori cadA failed to correct the deficiencies, whereas resistance to Cd(II) and Zn(II) was restored. Moreover, pY178 conferred increased Co(II) resistance to both the cadA mutants and the wild-type strain 69A. Heterologous expression of H. pylori cadA in an Escherichia coli zntA mutant resulted in an elevated resistance to Cd(II) and Zn(II). Expression of cadA in E. coli SE5000 harbouring H. pylori nixA, which encodes a divalent cation importer along with the H. pylori urease gene cluster, led to about a threefold increase in urease activity compared with E. coli control cells lacking the H. pylori cadA gene. These results suggest that H. pylori CadA is an essential resistance pump with ion specificity towards Cd(II), Zn(II) and Co(II). They also point to a possible role of H. pylori CadA in high-level activity of H. pylori urease, an enzyme sensitive to a variety of metal ions.
编码一种假定的过渡金属ATP酶的幽门螺杆菌cadA的失活仅在四种自然感受态幽门螺杆菌菌株之一（命名为69A）中实现。所有测试的cadA突变体对Cd(II)和Zn(II)的生长敏感性均增加。此外，其中一些突变体在生长期间63Ni积累减少，并且脲酶活性没有或受损，这并非由于缺乏脲酶亚基。用源自质粒（pY178）的幽门螺杆菌cadA进行的基因互补实验未能纠正这些缺陷，而对Cd(II)和Zn(II)的抗性得以恢复。此外，pY178赋予cadA突变体和野生型菌株69A对Co(II)的抗性增加。幽门螺杆菌cadA在大肠杆菌zntA突变体中的异源表达导致对Cd(II)和Zn(II)的抗性升高。在携带幽门螺杆菌nixA（其编码一种二价阳离子转运体）以及幽门螺杆菌脲酶基因簇的大肠杆菌SE5000中表达cadA，与缺乏幽门螺杆菌cadA基因的大肠杆菌对照细胞相比，脲酶活性提高了约三倍。这些结果表明，幽门螺杆菌CadA是一种对Cd(II)、Zn(II)和Co(II)具有离子特异性的必需抗性泵。它们还指出幽门螺杆菌CadA在幽门螺杆菌脲酶（一种对多种金属离子敏感的酶）的高水平活性中可能发挥的作用。
