近日，美国耶鲁大学Nikhil S. Malvankar团队揭示地杆菌纳米线的分泌基础。相关论文于2021年9月1日在线发表于国际学术期刊《自然》。
研究人员表示，地杆菌物种通过被称为微生物纳米线的表面附属物进行细胞外电子转移，这在一系列全球重要的环境现象中非常重要，并且在生物修复、生物能源、生物燃料和生物电子学方面也有应用。自2005年以来，这些纳米线一直被认为是仅由PilA-N蛋白组成的4型纤毛。然而，以前的结构分析表明，在细胞外电子转移过程中，细胞不产生纤毛，而是由细胞色素OmcS和OmcZ组成的纳米线。
研究人员发现，硫还原地杆菌将PilA-N与PilA-C结合在一起，从而组装异源纤毛，在需要细胞外电子转移的纳米线生产条件下，这些纤毛保持在外延状态。冷冻电子显微镜显示，PilA-N的C端残基通过静电和疏水相互作用使其与PilA-C的共聚稳定（形成PilA-N-C），使PilA-C沿着细丝的外表面定位。PilA-N-C丝缺乏芳香族侧链的π堆积，显示出比OmcZ纳米线低20,000倍的导电性。与表面显示的4型纤毛相比，PilA-N-C丝显示出与2型分泌假纤毛相似的结构、功能和定位。当pilA-N被删除时，OmcS和OmcZ纳米线的分泌就会消失，而当PilA-N-C细丝被重组时则会恢复。用其他微生物的4型纤毛替代pilA-N也会导致OmcZ纳米线的分泌损失。由于所有主要门类的原核生物都使用与4型纤毛类似的系统，这种纳米线的转移机制可能在确定不同的电子转移微生物的进化和流行方面具有广泛的影响，并为设计合成蛋白质纳米线来确定纳米线的组装结构。
附：英文原文
Title: Structure of Geobacter pili reveals secretory rather than nanowire behaviour
Author: Gu, Yangqi, Srikanth, Vishok, Salazar-Morales, Aldo I., Jain, Ruchi, OBrien, J. Patrick, Yi, Sophia M., Soni, Rajesh Kumar, Samatey, Fadel A., Yalcin, Sibel Ebru, Malvankar, Nikhil S.
Issue&Volume: 2021-09-01
Abstract: Extracellular electron transfer by Geobacter species through surface appendages known as microbial nanowires1 is important in a range of globally important environmental phenomena2, as well as for applications in bio-remediation, bioenergy, biofuels and bioelectronics. Since 2005, these nanowires have been thought to be type 4 pili composed solely of the PilA-N protein1. However, previous structural analyses have demonstrated that, during extracellular electron transfer, cells do not produce pili but rather nanowires made up of the cytochromes OmcS2,3 and OmcZ4. Here we show that Geobacter sulfurreducens binds PilA-N to PilA-C to assemble heterodimeric pili, which remain periplasmic under nanowire-producing conditions that require extracellular electron transfer5. Cryo-electron microscopy revealed that C-terminal residues of PilA-N stabilize its copolymerization with PilA-C (to form PilA-N–C) through electrostatic and hydrophobic interactions that position PilA-C along the outer surface of the filament. PilA-N–C filaments lack π-stacking of aromatic side chains and show a conductivity that is 20,000-fold lower than that of OmcZ nanowires. In contrast with surface-displayed type 4 pili, PilA-N–C filaments show structure, function and localization akin to those of type 2 secretion pseudopili6. The secretion of OmcS and OmcZ nanowires is lost when pilA-N is deleted and restored when PilA-N–C filaments are reconstituted. The substitution of pilA-N with the type 4 pili of other microorganisms also causes a loss of secretion of OmcZ nanowires. As all major phyla of prokaryotes use systems similar to type 4 pili, this nanowire translocation machinery may have a widespread effect in identifying the evolution and prevalence of diverse electron-transferring microorganisms and in determining nanowire assembly architecture for designing synthetic protein nanowires.
DOI: 10.1038/s41586-021-03857-w
Source: https://www.nature.com/articles/s41586-021-03857-w
Nature：《自然》，创刊于1869年。隶属于施普林格·自然出版集团，最新IF：69.504
官方网址：http://www.nature.com/
投稿链接：http://www.nature.com/authors/submit_manuscript.html
本期文章：《自然》：Online/在线发表
