Koedding Jiri, Howard Peter, Kaufmann Lindsay, Polzer Patrick, Lustig Ariel, Welte Wolfram
Fakultaet fuer Biologie, Universitaet Konstanz, Germany.
J Biol Chem. 2004 Mar 12;279(11):9978-86. doi: 10.1074/jbc.M311720200. Epub 2003 Dec 8.
FhuA belongs to a family of specific siderophore transport systems located in the outer membrane of Escherichia coli. The energy required for the transport process is provided by the proton motive force of the cytoplasmic membrane and is transmitted to FhuA by the protein TonB. Although the structure of full-length TonB is not known, the structure of the last 77 residues of a fragment composed of the 86 C-terminal amino acids was recently solved and shows an intertwined dimer (Chang, C., Mooser, A., Pluckthun, A., and Wlodawer, A. (2001) J. Biol. Chem. 276, 27535-27540). We analyzed the ability of truncated C-terminal TonB fragments of different lengths (77, 86, 96, 106, 116, and 126 amino acid residues, respectively) to bind to the receptor FhuA. Only the shortest TonB fragment, TonB-77, could not effectively interact with FhuA. We have also observed that the fragments TonB-77 and TonB-86 form homodimers in solution, whereas the longer fragments remain monomeric. TonB fragments that bind to FhuA in vitro also inhibit ferrichrome uptake via FhuA in vivo and protect cells against attack by bacteriophage Phi80.
FhuA属于位于大肠杆菌外膜的特定铁载体转运系统家族。转运过程所需的能量由细胞质膜的质子动力提供,并通过蛋白质TonB传递给FhuA。尽管全长TonB的结构尚不清楚,但最近解析了由86个C端氨基酸组成的片段的最后77个残基的结构,该结构显示为一个缠绕的二聚体(Chang, C., Mooser, A., Pluckthun, A., and Wlodawer, A. (2001) J. Biol. Chem. 276, 27535 - 27540)。我们分析了不同长度(分别为77、86、96、106、116和126个氨基酸残基)的截短C端TonB片段与受体FhuA结合的能力。只有最短的TonB片段TonB - 77不能有效地与FhuA相互作用。我们还观察到,片段TonB - 77和TonB - 86在溶液中形成同型二聚体,而较长的片段保持单体状态。在体外与FhuA结合的TonB片段在体内也抑制通过FhuA的高铁色素摄取,并保护细胞免受噬菌体Phi80的攻击。