Department of Medicine, University of Virginia, Charlottesville, Virginia, United States of America.
PLoS One. 2011;6(9):e24611. doi: 10.1371/journal.pone.0024611. Epub 2011 Sep 8.
The lipoprotein encoded by the Francisella tularensis subsp. tularensis locus FTT1103 is essential for virulence; an FTT1103 deletion mutant is defective in uptake and intracellular survival, and mice survive high dose challenges of greater than 10(8) bacteria. This protein has two conserved domains; one is found in a class of virulence proteins called macrophage infectivity potentiator (Mip) proteins, and the other in oxidoreductase Disulfide Bond formation protein A (DsbA)-related proteins. We have designated the protein encoded by FTT1103 as FipB for Francisellainfectivity potentiator protein B. The locus FTT1102 (fipA), which is upstream of fipB, also has similarity to same conserved Mip domain. Deletion and site-specific mutants of fipA and fipB were constructed in the Schu S4 strain, and characterized with respect to intracellular replication and in vivo virulence. A nonpolar fipA mutant demonstrated reduced survival in host cells, but was only slightly attenuated in vivo. Although FipB protein was present in a fipA mutant, the abundance of the three isoforms of FipB was altered, suggesting that FipA has a role in post-translational modification of FipB. Similar to many DsbA homologues, FipB contains a cysteine-any amino acid-any amino acid-cysteine (CXXC) motif. This motif was found to be important for FipB's role in virulence; a deletion mutant complemented with a gene encoding a FipB protein in which the first cysteine was changed to an alanine residue (AXXC) failed to restore intracellular survival or in vivo virulence. Complementation with a gene that encoded a CXXA containing FipB protein was significantly defective in intracellular growth; however, only slightly attenuated in vivo.
弗朗西斯氏菌亚种 Francisella tularensis 编码的脂蛋白 FTT1103 对毒力至关重要；FTT1103 缺失突变体在摄取和细胞内生存方面存在缺陷，并且在高剂量大于 10(8)细菌的挑战中，老鼠得以存活。该蛋白具有两个保守结构域；一个存在于一类称为巨噬细胞感染增强蛋白（Mip）的毒力蛋白中，另一个存在于氧化还原酶二硫键形成蛋白 A（DsbA）相关蛋白中。我们将 FTT1103 编码的蛋白命名为 FipB，即 Francisellainfectivity potentiator protein B。FTT1102（fipA）位于 fipB 上游，与相同的保守 Mip 结构域也具有相似性。在 Schu S4 株中构建了 fipA 和 fipB 的缺失和定点突变体，并对其在细胞内复制和体内毒力进行了研究。fipA 非极性突变体在宿主细胞中的存活率降低，但在体内仅略微减弱。尽管 FipB 蛋白存在于 fipA 突变体中，但三种 FipB 同工型的丰度发生了改变，表明 FipA 在 FipB 的翻译后修饰中起作用。与许多 DsbA 同源物一样，FipB 包含一个半胱氨酸-任意氨基酸-任意氨基酸-半胱氨酸（CXXC）基序。该基序对于 FipB 的毒力作用非常重要；用编码一个 FipB 蛋白的基因进行互补，其中第一个半胱氨酸被改变为丙氨酸残基（AXXC）的缺失突变体不能恢复细胞内生存或体内毒力。用编码含有 CXXA 的 FipB 蛋白的基因进行互补的能力显著受损，在细胞内生长；然而，在体内仅略微减弱。
