The Gram-negative bacterium Pseudomonas aeruginosa secretes many proteins into the extracellular medium. At least two distinct secretion pathways can be discerned. The majority of the exoproteins are secreted via a two-step mechanism. These proteins are first translocated across the inner membrane in a signal sequence-dependent fashion. The subsequent translocation across the outer membrane requires the products of at least 12 distinct xcp genes. The exact role of one of these proteins, the XcpA protein, has been resolved. It is a peptidase that is required for the processing of the precursors of four other Xcp proteins, thus allowing their assembly into the secretion apparatus. This peptidase is also required for the processing of the precursors of type IV pili subunits. Two other Xcp proteins, XcpR and XcpS, display extensive homology to proteins involved in pili biogenesis, which suggests that the assembly of the secretion apparatus and the biogenesis of type IV pili are related processes. The secretion of alkaline protease does not require the xcp gene products. This enzyme, which is encoded by the aprA gene, is not synthesized in a precursor form with an N-terminal signal sequence. Secretion across the two membranes probably takes place in one step at adhesion zones that may be constituted by three accessory proteins, designated AprD, AprE and AprF. The two secretion pathways found in P. aeruginosa appear to have disseminated widely among Gram-negative bacteria.

中文翻译：

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铜绿假单胞菌中的蛋白质分泌。

革兰氏阴性细菌铜绿假单胞菌将许多蛋白质分泌到细胞外培养基中。可以识别至少两种不同的分泌途径。大多数外泌蛋白是通过两步机制分泌的。这些蛋白质首先以信号序列依赖性方式跨内膜转运。随后跨外膜的移位需要至少12个不同的xcp基因的产物。这些蛋白之一XcpA蛋白的确切作用已得到解决。这是肽酶，是加工其他四种Xcp蛋白前体所必需的，因此可以将它们组装到分泌设备中。该肽酶对于加工IV型菌毛亚基的前体也是必需的。另外两个Xcp蛋白XcpR和XcpS，与菌毛生物发生有关的蛋白质显示出广泛的同源性，这表明分泌装置的组装和IV型菌毛的生物发生是相关的过程。碱性蛋白酶的分泌不需要xcp基因产物。这种由aprA基因编码的酶不是以具有N端信号序列的前体形式合成的。跨两层膜的分泌可能一步发生在黏附区域，黏附区域可能由三种辅助蛋白质（称为AprD，AprE和AprF）构成。铜绿假单胞菌中发现的两个分泌途径似乎已在革兰氏阴性细菌中广泛传播。碱性蛋白酶的分泌不需要xcp基因产物。这种由aprA基因编码的酶不是以具有N端信号序列的前体形式合成的。跨两层膜的分泌可能一步发生在黏附区域，黏附区域可能由三种辅助蛋白质（称为AprD，AprE和AprF）构成。铜绿假单胞菌中发现的两个分泌途径似乎已在革兰氏阴性细菌中广泛传播。碱性蛋白酶的分泌不需要xcp基因产物。这种由aprA基因编码的酶不是以具有N端信号序列的前体形式合成的。跨两层膜的分泌可能一步发生在黏附区域，黏附区域可能由三种辅助蛋白质（称为AprD，AprE和AprF）构成。铜绿假单胞菌中发现的两个分泌途径似乎已在革兰氏阴性细菌中广泛传播。