Department of Microbiology and Immunology, School of Medicine, University of North Carolina, Chapel Hill, NC 27599-7290, USA.
Mol Microbiol. 2012 Nov;86(4):988-1006. doi: 10.1111/mmi.12036. Epub 2012 Oct 5.
Two-partner secretion (TPS) systems use β-barrel proteins of the Omp85-TpsB superfamily to transport large exoproteins across the outer membranes of Gram-negative bacteria. The Bordetella FHA/FhaC proteins are prototypical of TPS systems in which the exoprotein contains a large C-terminal prodomain that is removed during translocation. Although it is known that the FhaB prodomain is required for FHA function in vivo, its role in FHA maturation has remained mysterious. We show here that the FhaB prodomain is required for the extracellularly located mature C-terminal domain (MCD) of FHA to achieve its proper conformation. We show that the C-terminus of the prodomain is retained intracellularly and that sequences within the N-terminus of the prodomain are required for this intracellular localization. We also identify sequences at the C-terminus of the MCD that are required for release of mature FHA from the cell surface. Our data support a model in which the intracellularly located prodomain affects the final conformation of the extracellularly located MCD. We hypothesize that maturation triggers cleavage and degradation of the prodomain.
双伙伴分泌（TPS）系统使用 Omp85-TpsB 超家族的β-桶蛋白将大的外分泌蛋白穿过革兰氏阴性细菌的外膜运输。博德特氏菌 FHA/FhaC 蛋白是 TPS 系统的典型代表，其中外分泌蛋白含有一个大的 C 端前导序列，在转运过程中被切除。虽然已知 FhaB 前导序列对于 FHA 在体内的功能是必需的，但它在 FHA 成熟中的作用仍然是神秘的。我们在这里表明，FhaB 前导序列对于 FHA 的成熟 C 端结构域（MCD）在细胞外达到其适当构象是必需的。我们表明，前导序列的 C 端在细胞内被保留，并且前导序列的 N 端内的序列对于这种细胞内定位是必需的。我们还鉴定了 MCD 的 C 端上的序列，这些序列对于成熟 FHA 从细胞表面的释放是必需的。我们的数据支持这样一种模型，即细胞内定位的前导序列影响细胞外定位的 MCD 的最终构象。我们假设成熟触发前导序列的切割和降解。
