Kampfenkel K, Braun V
Universität Tübingen, Germany.
J Bacteriol. 1992 Aug;174(16):5485-7. doi: 10.1128/jb.174.16.5485-5487.1992.
The ExbD protein is involved in the energy-coupled transport of ferric siderophores, vitamin B12, and B-group colicins across the outer membrane of Escherichia coli. In order to study ExbD membrane topology, ExbD-beta-lactamase fusion proteins were constructed. Cells expressing beta-lactamase fusions to residues 53, 57, 70, 76, 78, 80, 92, 121, and 134 of ExbD displayed high levels of ampicillin resistance, whereas fusions to residues 9 and 19 conferred no ampicillin resistance. It is concluded that the only hydrophobic segment of ExbD, encompassing residues 23 to 43, forms a transmembrane domain and that residues 1 to 22 are located in the cytoplasm and residues 44 to 141 are located in the periplasm.
ExbD蛋白参与铁载体、维生素B12和B族大肠杆菌素跨大肠杆菌外膜的能量偶联转运。为了研究ExbD的膜拓扑结构，构建了ExbD-β-内酰胺酶融合蛋白。表达ExbD第53、57、70、76、78、80、92、121和134位残基与β-内酰胺酶融合蛋白的细胞表现出高水平的氨苄青霉素抗性，而与第9和19位残基的融合蛋白则不具有氨苄青霉素抗性。得出的结论是，ExbD唯一的疏水片段（包含第23至43位残基）形成一个跨膜结构域，第1至22位残基位于细胞质中，第44至141位残基位于周质中。
