Roberts Cameron S, Gura Colby, Sandkvist Maria
bioRxiv. 2025 Sep 10:2025.09.09.675180. doi: 10.1101/2025.09.09.675180.
Gram-negative bacteria employ the Type II Secretion System (T2SS) to not only secrete an array of soluble effectors such as toxins to the extracellular space, but also to facilitate the surface localization of enzymes and adhesins that are beneficial to life in different environments. For example, the pullulan degrading enzyme pullulanase (PulA) from and the recently discovered adhesin InvL from are initially expressed with a lipobox containing signal peptide, resulting in their N-terminal acylation and subsequent surface anchoring after T2SS mediated export. While outer membrane translocation of both soluble and surface associated T2SS effectors depends on the T2SS secretin GspD, it is unclear how lipoproteins are accommodated by the T2SS during transport to the cell surface. Here, we identify a role for GspN in the outer membrane translocation of InvL in the opportunistic pathogen . Additional putative lipoproteins are found to have a similar GspN dependence for secretion, while soluble proteins are secreted independently of GspN. We demonstrate that a specific sorting motif C-terminal to the lipobox is required for GspN-dependent surface localization. Based on structural predictions, GspN belongs to the larger AsmA-like protein family that includes both eukaryotic and prokaryotic members. This protein family has been implicated in phospholipid transport, but here we expand the role for this family to include transport of lipoproteins. We also confirm that the GspN homolog PulN is required for PulA surface localization in .
The Type II Secretion (T2SS) is considered a virulence factor of gram-negative pathogens such as . The role of one of the components of the T2SS, GspN, has been unclear and many studies across multiple model systems have reported that GspN is dispensable for protein secretion. Here, we characterize the transport of a subset of proteins t by the T2SS and show that GspN is required for their outer membrane translocation and surface localization. GspN belongs to the AsmA-like protein family, which to date has only been implicated in the transport of phospholipids. This study demonstrates that, in addition to transport of phospholipids, this class of proteins also facilitates the secretion of proteins.
革兰氏阴性菌利用Ⅱ型分泌系统（T2SS）不仅将一系列可溶性效应蛋白（如毒素）分泌到细胞外空间，还促进酶和黏附素在表面的定位，这些对在不同环境中的生存有益。例如，来自[具体菌名1]的支链淀粉酶降解酶支链淀粉酶（PulA）和最近发现的来自[具体菌名2]的黏附素InvL最初表达时带有含信号肽的脂盒，导致其N端酰化，并在T2SS介导的输出后进行表面锚定。虽然可溶性和表面相关的T2SS效应蛋白的外膜转运都依赖于T2SS分泌素GspD，但脂蛋白在转运到细胞表面过程中如何被T2SS容纳尚不清楚。在这里，我们确定了GspN在机会致病菌[具体菌名3]中InvL外膜转运中的作用。发现其他推定的脂蛋白在分泌方面对GspN有类似的依赖性，而可溶性蛋白的分泌则不依赖于GspN。我们证明脂盒C端的特定分选基序是GspN依赖性表面定位所必需的。基于结构预测，GspN属于更大的AsmA样蛋白家族，该家族包括真核和原核成员。这个蛋白家族与磷脂转运有关，但在这里我们将这个家族的作用扩展到包括脂蛋白的转运。我们还证实GspN同源物PulN是[具体菌名4]中PulA表面定位所必需的。
Ⅱ型分泌（T2SS）被认为是革兰氏阴性病原体（如[具体菌名5]）的毒力因子。T2SS的一个组成部分GspN的作用尚不清楚，多个模型系统的许多研究报告称GspN对于蛋白质分泌是可有可无的。在这里，我们描述了T2SS对一部分蛋白质的转运，并表明GspN是它们外膜转运和表面定位所必需的。GspN属于AsmA样蛋白家族，迄今为止该家族仅与磷脂转运有关。这项研究表明，除了磷脂转运外，这类蛋白还促进蛋白质的分泌。
