Barbat Brice, Douzi Badreddine, Ball Geneviève, Tribout Mathilde, El Karkouri Khalid, Kellenberger Christine, Voulhoux Romé
LCB-UMR7283, CNRS, Aix Marseille Université, IMM, Marseille, France.
Université de Lorraine, INRAE, DynAMic, Nancy, F-54000 France.
Sci Adv. 2023 Oct 6;9(40):eadg6996. doi: 10.1126/sciadv.adg6996. Epub 2023 Oct 4.
Secretins are outer membrane (OM) channels found in various bacterial nanomachines that secrete or assemble large extracellular structures. High-resolution 3D structures of type 2 secretion system (T2SS) secretins revealed bimodular channels with a C-module, holding a conserved central gate and an optional top gate, followed by an N-module for which multiple structural organizations have been proposed. Here, we perform a structure-driven in vivo study of the XcpD secretin, which validates one of the organizations of the N-module whose flexibility enables alternative conformations. We also show the existence of the central gate in vivo and its required flexibility, which is key for substrate passage and watertightness control. Last, functional, genomic, and phylogenetic analyses indicate that the optional top gate provides a gain of watertightness. Our data illustrate how the gating properties of T2SS secretins allow these large channels to overcome the duality between the necessity of preserving the OM impermeability while simultaneously promoting the secretion of large, folded effectors.
分泌素是存在于各种细菌纳米机器中的外膜通道，这些纳米机器可分泌或组装大型细胞外结构。2型分泌系统（T2SS）分泌素的高分辨率三维结构揭示了双模块通道，其具有一个C模块，包含一个保守的中央门和一个可选的顶门，随后是一个N模块，人们已提出了该模块的多种结构组织形式。在此，我们对XcpD分泌素进行了一项基于结构的体内研究，该研究验证了N模块的一种组织形式，其灵活性使得能够形成不同的构象。我们还展示了中央门在体内的存在及其所需的灵活性，这是底物通过和水密性控制的关键。最后，功能、基因组和系统发育分析表明，可选的顶门提高了水密性。我们的数据说明了T2SS分泌素的门控特性如何使这些大型通道克服在保持外膜不透性的同时促进大型折叠效应蛋白分泌的必要性之间的矛盾。
