Braun V, Killmann H, Benz R
Mikrobiologie/Membranphysiologie, Universität Tübingen, Germany.
FEBS Lett. 1994 Jun 6;346(1):59-64. doi: 10.1016/0014-5793(94)00431-5.
Active transport of Fe3+ as ferrichrome complex through the outer membrane of Escherichia coli is mediated by the FhuA outer membrane protein and the TonB-ExbB-ExbD protein complex in the cytoplasmic membrane. The required energy is provided by the electrochemical potential of the cytoplasmic membrane which is assumed to induce a conformation of the TonB protein that causes a conformational change in FhuA so that bound ferrichrome is released into the periplasmic space located between the outer and the cytoplasmic membrane. Excision of segments as small as 12 amino acids in the largest surface loop of FhuA converted FhuA into an open channel through which ferrichrome and antibiotics diffused independent of TonB-ExbB-ExbD. It is proposed that FhuA forms a closed channel which is opened by movement of the gating loop through a kind of allosteric interaction with TonB. The gating loop is also involved in binding of all FhuA ligands which in addition to ferrichrome are the phages T1, T5, phi 80, colicin M and the antibiotic albomycin.
作为铁载体复合物的Fe3+通过大肠杆菌外膜的主动运输由外膜蛋白FhuA和细胞质膜中的TonB-ExbB-ExbD蛋白复合物介导。所需能量由细胞质膜的电化学势提供，该电化学势被认为会诱导TonB蛋白的构象，从而导致FhuA发生构象变化，使结合的铁载体释放到位于外膜和细胞质膜之间的周质空间中。在FhuA最大表面环中切除小至12个氨基酸的片段，会将FhuA转化为一个开放通道，铁载体和抗生素可通过该通道独立于TonB-ExbB-ExbD进行扩散。有人提出，FhuA形成一个封闭通道，该通道通过门控环与TonB的一种变构相互作用而打开。门控环还参与所有FhuA配体的结合，除了铁载体外，这些配体还包括噬菌体T1、T5、phi 80、大肠菌素M和抗生素白霉素。
