Department of Microbiology, University of Washington, Seattle, Washington, USA
School of Life Sciences, University of Nevada Las Vegas, Las Vegas, Nevada, USA.
mBio. 2018 Apr 10;9(2):e00543-18. doi: 10.1128/mBio.00543-18.
produces an extracellular biofilm matrix that consists of nucleic acids, exopolysaccharides, lipid vesicles, and proteins. In general, the protein component of the biofilm matrix is poorly defined and understudied relative to the other major matrix constituents. While matrix proteins have been suggested to provide many functions to the biofilm, only proteins that play a structural role have been characterized thus far. Here we identify proteins enriched in the matrix of biofilms. We then focused on a candidate matrix protein, the serine protease inhibitor ecotin (PA2755). This protein is able to inhibit neutrophil elastase, a bactericidal enzyme produced by the host immune system during biofilm infections. We show that ecotin binds to the key biofilm matrix exopolysaccharide Psl and that it can inhibit neutrophil elastase when associated with Psl. Finally, we show that ecotin protects both planktonic and biofilm cells from neutrophil elastase-mediated killing. This may represent a novel mechanism of protection for biofilms to increase their tolerance against the innate immune response. Proteins associated with the extracellular matrix of bacterial aggregates called biofilms have long been suggested to provide many important functions to the community. To date, however, only proteins that provide structural roles have been described, and few matrix-associated proteins have been identified. We developed a method to identify matrix proteins and characterized one. We show that this protein, when associated with the biofilm matrix, can inhibit a bactericidal enzyme produced by the immune system during infection and protect biofilm cells from death induced by the enzyme. This may represent a novel mechanism of protection for biofilms, further increasing their tolerance against the immune response. Together, our results are the first to show a nonstructural function for a confirmed matrix-interacting protein.
产生一种细胞外生物膜基质，由核酸、胞外多糖、脂囊泡和蛋白质组成。一般来说，生物膜基质的蛋白质成分相对于其他主要基质成分定义不明确，研究也较少。虽然已经提出基质蛋白对生物膜有许多功能，但迄今为止仅对具有结构作用的蛋白进行了表征。在这里，我们鉴定了生物膜基质中丰富的蛋白质。然后，我们将重点放在候选基质蛋白丝氨酸蛋白酶抑制剂 ecotin（PA2755）上。这种蛋白质能够抑制中性粒细胞弹性蛋白酶，这是宿主免疫系统在生物膜感染期间产生的一种杀菌酶。我们表明，ecotin 结合到关键的生物膜基质胞外多糖 Psl 上，并且当与 Psl 结合时，它可以抑制中性粒细胞弹性蛋白酶。最后，我们表明 ecotin 可以保护浮游和生物膜细胞免受中性粒细胞弹性蛋白酶介导的杀伤。这可能代表生物膜增加其对先天免疫反应的耐受性的一种新的保护机制。长期以来，人们一直认为聚集在一起的细菌的细胞外基质中的蛋白质（称为生物膜）可以为群落提供许多重要的功能。然而，迄今为止，仅描述了提供结构作用的蛋白质，并且仅鉴定了少数基质相关蛋白。我们开发了一种鉴定基质蛋白的方法，并对其中一种进行了表征。我们表明，这种蛋白质与生物膜基质结合时，可以抑制感染过程中免疫系统产生的一种杀菌酶，并保护生物膜细胞免受该酶诱导的死亡。这可能代表了生物膜的一种新的保护机制，进一步提高了它们对免疫反应的耐受性。总的来说，我们的结果首次表明一种已确认的基质相互作用蛋白具有非结构功能。
