Lasica Anna M, Ksiazek Miroslaw, Madej Mariusz, Potempa Jan
Department of Oral Immunology and Infectious Diseases, University of Louisville School of DentistryLouisville, KY, United States.
Department of Bacterial Genetics, Faculty of Biology, Institute of Microbiology, University of WarsawWarsaw, Poland.
Front Cell Infect Microbiol. 2017 May 26;7:215. doi: 10.3389/fcimb.2017.00215. eCollection 2017.
Protein secretion systems are vital for prokaryotic life, as they enable bacteria to acquire nutrients, communicate with other species, defend against biological and chemical agents, and facilitate disease through the delivery of virulence factors. In this review, we will focus on the recently discovered type IX secretion system (T9SS), a complex translocon found only in some species of the phylum. T9SS plays two roles, depending on the lifestyle of the bacteria. It provides either a means of movement (called gliding motility) for peace-loving environmental bacteria or a weapon for pathogens. The best-studied members of these two groups are , a commensal microorganism often found in water and soil, and , a human oral pathogen that is a major causative agent of periodontitis. In and some other periodontopathogens, T9SS translocates proteins, especially virulence factors, across the outer membrane (OM). Proteins destined for secretion bear a conserved C-terminal domain (CTD) that directs the cargo to the OM translocon. At least 18 proteins are involved in this still enigmatic process, with some engaged in the post-translational modification of T9SS cargo proteins. Upon translocation across the OM, the CTD is removed by a protease with sortase-like activity and an anionic LPS is attached to the newly formed C-terminus. As a result, a cargo protein could be secreted into the extracellular milieu or covalently attached to the bacterial surface. T9SS is regulated by a two-component system; however, the precise environmental signal that triggers it has not been identified. Exploring unknown systems contributing to bacterial virulence is exciting, as it may eventually lead to new therapeutic strategies. During the past decade, the major components of T9SS were identified, as well as hints suggesting the possible mechanism of action. In addition, the list of characterized cargo proteins is constantly growing. The actual structure of the translocon, situated in the OM of bacteria, remains the least explored area; however, new technical approaches and increasing scientific attention have resulted in a growing body of data. Therefore, we present a compact up-to-date review of this topic.
蛋白质分泌系统对原核生物的生存至关重要，因为它们使细菌能够获取营养、与其他物种交流、抵御生物和化学因子，并通过传递毒力因子促进疾病发生。在本综述中，我们将聚焦于最近发现的IX型分泌系统（T9SS），这是一种仅在该菌门某些物种中发现的复杂转运体。T9SS发挥两种作用，这取决于细菌的生活方式。它为爱好和平的环境细菌提供一种运动方式（称为滑行运动），或者为病原体提供一种武器。这两组中研究得最透彻的成员分别是，一种常在水和土壤中发现的共生微生物，以及，一种人类口腔病原体，是牙周炎的主要致病因子。在和其他一些牙周病原体中，T9SS将蛋白质，尤其是毒力因子，转运穿过外膜（OM）。 destined for secretion bear a conserved C-terminal domain (CTD) that directs the cargo to the OM translocon. At least 18 proteins are involved in this still enigmatic process, with some engaged in the post-translational modification of T9SS cargo proteins. Upon translocation across the OM, the CTD is removed by a protease with sortase-like activity and an anionic LPS is attached to the newly formed C-terminus. As a result, a cargo protein could be secreted into the extracellular milieu or covalently attached to the bacterial surface. T9SS由一个双组分系统调控；然而，尚未确定触发它的确切环境信号。探索有助于细菌毒力的未知系统令人兴奋，因为这最终可能会带来新的治疗策略。在过去十年中，T9SS的主要成分已被确定，同时也有线索暗示其可能的作用机制。此外，已鉴定的货物蛋白列表也在不断增加。位于细菌外膜中的转运体的实际结构仍是研究最少的领域；然而，新的技术方法和越来越多的科学关注已产生了越来越多的数据。因此，我们对这一主题进行了简洁的最新综述。 （注：原文中存在部分不完整表述，翻译时尽量按照原文呈现，但这可能会影响译文的连贯性和逻辑性。）
