Günter K, Braun V
Mikrobiologie II, Universität Tübingen, Federal Republic of Germany.
Mol Gen Genet. 1988 Dec;215(1):69-75. doi: 10.1007/BF00331305.
The FhuA protein (formerly TonA) is located in the outer membrane of Escherichia coli K12. Fusions between fhuA and phoA genes were constructed. They determined proteins containing a truncated but still active alkaline phosphatase of constant size and a variable FhuA portion which ranged from 11%-90% of the mature FhuA protein. The fusion sites were nearly randomly distributed along the FhuA protein. The FhuA segments directed the secretion of the truncated alkaline phosphatase across the cytoplasmic membrane. The fusion proteins were proteolytically degraded up to the size of alkaline phosphatase and no longer reacted with anti-FhuA antibodies. The fusion proteins were more stable in lon and pep mutants lacking cytoplasmic protease and peptidases, respectively. The larger fusion proteins above a molecular weight of 64,000 dalton were predominantly found in the outer membrane fraction. They were degraded by trypsin when cells were converted to spheroplasts so that trypsin gained access to the periplasm. In contrast, FhuA protein in the outer membrane was largely resistant to trypsin. It is concluded that the larger FhuA'-'PhoA fusion proteins were associated with, but not properly integrated into, the outer membrane.
FhuA蛋白（以前称为TonA）位于大肠杆菌K12的外膜中。构建了fhuA和phoA基因之间的融合体。他们确定了含有截短但仍具活性的恒定大小碱性磷酸酶以及可变FhuA部分的蛋白质，该FhuA部分占成熟FhuA蛋白的11%-90%。融合位点几乎随机分布在FhuA蛋白上。FhuA片段引导截短的碱性磷酸酶穿过细胞质膜进行分泌。融合蛋白被蛋白水解降解至碱性磷酸酶大小，不再与抗FhuA抗体反应。融合蛋白在分别缺乏细胞质蛋白酶和肽酶的lon和pep突变体中更稳定。分子量高于64,000道尔顿的较大融合蛋白主要存在于外膜部分。当细胞转化为原生质球时，它们会被胰蛋白酶降解，从而使胰蛋白酶能够进入周质。相比之下，外膜中的FhuA蛋白对胰蛋白酶具有很大抗性。得出的结论是，较大的FhuA'-'PhoA融合蛋白与外膜相关，但未正确整合到外膜中。
