Killmann H, Herrmann C, Wolff H, Braun V
Mikrobiologie/Membranphysiologie, Universität Tübingen, D-72076 Tübingen, Germany.
J Bacteriol. 1998 Aug;180(15):3845-52. doi: 10.1128/JB.180.15.3845-3852.1998.
The fhuA genes of Salmonella paratyphi B, Salmonella typhimurium, and Pantoea agglomerans were sequenced and compared with the known fhuA sequence of Escherichia coli. The highly similar FhuA proteins displayed the largest difference in the predicted gating loop, which in E. coli controls the permeability of the FhuA channel and serves as the principal binding site for the phages T1, T5, and phi80. All the FhuA proteins contained the region in the gating loops required in E. coli for ferrichrome and albomycin transport. The three subdomains required for phage binding were contained in the gating loop of S. paratyphi B which is infected by the E. coli phages, whereas two of the subdomains were deleted in S. typhimurium and P. agglomerans which are resistant to the E. coli phages. Small deletions in a surface loop adjacent to the gating loop, residues 236 to 243 and 236 to 248, inactivated E. coli FhuA with regard to transport of ferrichrome and albomycin, but sensitivity to T1 and T5 was fully retained and sensitivity to phi80 and colicin M was reduced 10-fold. Full-size FhuA hybrid proteins of S. paratyphi B and S. typhimurium displayed S. paratyphi B FhuA activity when the hybrids contained two-thirds of either the N- or the C-terminal portions of S. paratyphi B and displayed S. typhimurium FhuA activity to phage ES18 when the hybrid contained two-thirds of the N-terminal region of the S. typhimurium FhuA. The central segment of the S. paratyphi B FhuA flanked on both sides by S. typhimurium FhuA regions conferred full sensitivity only to phage T5. The data support the essential role of the gating loop for the transport of ferrichrome and albomycin, identified an additional loop for ferrichrome and albomycin uptake, and suggest that several segments and their proper conformation, determined by the entire FhuA protein, contribute to the multiple FhuA activities.
对副伤寒沙门氏菌B、鼠伤寒沙门氏菌和成团泛菌的fhuA基因进行了测序，并与已知的大肠杆菌fhuA序列进行了比较。高度相似的FhuA蛋白在预测的门控环中显示出最大差异，在大肠杆菌中，该环控制FhuA通道的通透性，并作为噬菌体T1、T5和phi80的主要结合位点。所有FhuA蛋白在门控环中都含有大肠杆菌中铁转运菌素和阿波霉素转运所需的区域。被大肠杆菌噬菌体感染的副伤寒沙门氏菌B的门控环中包含噬菌体结合所需的三个亚结构域，而对大肠杆菌噬菌体具有抗性的鼠伤寒沙门氏菌和成团泛菌中两个亚结构域缺失。与门控环相邻的一个表面环（残基236至243和236至248）中的小缺失使大肠杆菌FhuA在铁转运菌素和阿波霉素转运方面失活，但对T1和T5的敏感性完全保留，对phi80和大肠杆菌素M的敏感性降低了10倍。当杂种包含副伤寒沙门氏菌B三分之二的N端或C端部分时，副伤寒沙门氏菌B和鼠伤寒沙门氏菌的全长FhuA杂合蛋白表现出副伤寒沙门氏菌B FhuA活性；当杂种包含鼠伤寒沙门氏菌FhuA三分之二的N端区域时，对噬菌体ES18表现出鼠伤寒沙门氏菌FhuA活性。副伤寒沙门氏菌B FhuA的中央片段两侧为鼠伤寒沙门氏菌FhuA区域，仅对噬菌体T5具有完全敏感性。这些数据支持了门控环在铁转运菌素和阿波霉素转运中的重要作用，确定了另一个铁转运菌素和阿波霉素摄取环，并表明由整个FhuA蛋白决定的几个片段及其正确构象有助于多种FhuA活性。
