Sonani Ravi R, Liu Ying, Xiang Jialin, Cvirkaite-Krupovic Virginija, Du Shishen, Chen Xiangdong, Krupovic Mart, Egelman Edward H
Department of Biochemistry and Molecular Genetics, University of Virginia Medical School, Charlottesville, VA 22903.
Cell Biology and Virology of Archaea Unit, Institut Pasteur, Université Paris Cité, CNRS UMR6047, Paris 75015, France.
Proc Natl Acad Sci U S A. 2025 Aug 5;122(31):e2514980122. doi: 10.1073/pnas.2514980122. Epub 2025 Jul 30.
Diverse extracellular filaments present on the surface of archaea mediate multiple key processes, such as motility, adhesion, and biofilm formation. Although several archaeal filament types have been characterized in considerable detail, many remain understudied, particularly those utilizing noncanonical secretion systems. Here, we describe the Tafi bundling pilus that facilitates biofilm formation in the haloarchaeon sp. J7-2. Unlike previously characterized archaeal pili, Tafi is secreted via the twin-arginine translocation (Tat) pathway, which transports fully folded proteins across the cytoplasmic membrane. Structural analysis reveals that although Tafi pili assemble via a canonical strand-donation mechanism, the pilin subunit (TafE) adopts a distinct structural topology that sets it apart from the previously characterized Sec-dependent pilins that form bundling pili in archaea. Sequence analyses show that TafE homologs are also present in thermophilic archaea from different phyla, but Tat-signal sequences are exclusive to pilins of halophilic archaea. Nevertheless, we find that Tat signal peptides in haloarchaeal TafE-like pili were exchanged back to the Sec signal peptides on multiple independent occasions. These findings expand our understanding of the diversity and evolution of archaeal extracellular filaments and highlight the Tat pathway as a route for pilus assembly in halophilic archaea.
古菌表面存在的多种细胞外丝介导多种关键过程，如运动性、黏附以及生物膜形成。尽管几种古菌丝状类型已得到相当详细的表征，但许多仍未得到充分研究，尤其是那些利用非经典分泌系统的丝状类型。在此，我们描述了促进嗜盐古菌J7 - 2菌株生物膜形成的塔菲（Tafi）成束菌毛。与先前表征的古菌菌毛不同，Tafi通过双精氨酸转运（Tat）途径分泌，该途径可将完全折叠的蛋白质转运穿过细胞质膜。结构分析表明，尽管Tafi菌毛通过典型的链捐赠机制组装，但菌毛蛋白亚基（TafE）采用了独特的结构拓扑结构，使其有别于先前表征的在古菌中形成成束菌毛的依赖Sec的菌毛蛋白。序列分析表明，TafE同源物也存在于来自不同门的嗜热古菌中，但Tat信号序列仅存在于嗜盐古菌的菌毛蛋白中。然而，我们发现嗜盐古菌中类似TafE的菌毛中的Tat信号肽在多个独立情况下被交换回Sec信号肽。这些发现扩展了我们对古菌细胞外丝的多样性和进化的理解，并突出了Tat途径作为嗜盐古菌中菌毛组装的一条途径。
