Nair Divya B, Jarrell Ken F
Department of Biomedical and Molecular Sciences, Queen's University, Kingston, ON K7L 3N6, Canada.
Life (Basel). 2015 Jan 5;5(1):85-101. doi: 10.3390/life5010085.
Methanococcus maripaludis has two different surface appendages: type IV-like pili and archaella. Both structures are believed to be assembled using a bacterial type IV pilus mechanism. Each structure is composed of multiple subunits, either pilins or archaellins. Both pilins and archaellins are made initially as preproteins with type IV pilin-like signal peptides, which must be removed by a prepilin peptidase-like enzyme. This enzyme is FlaK for archaellins and EppA for pilins. In addition, both pilins and archaellins are modified with N-linked glycans. The archaellins possess an N-linked tetrasaccharide while the pilins have a pentasaccharide which consists of the archaellin tetrasaccharide but with an additional sugar, an unidentified hexose, attached to the linking sugar. In this report, we show that archaellins can be processed by FlaK in the absence of N-glycosylation and N-glycosylation can occur on archaellins that still retain their signal peptides. In contrast, pilins are not glycosylated unless they have been acted on by EppA to have the signal peptide removed. However, EppA can still remove signal peptides from non-glycosylated pilins. These findings indicate that there is a difference in the order of the posttranslational modifications of pilins and archaellins even though both are type IV pilin-like proteins.
类IV型菌毛和古菌鞭毛。这两种结构都被认为是利用细菌IV型菌毛机制组装而成的。每种结构都由多个亚基组成，即菌毛蛋白或古菌鞭毛蛋白。菌毛蛋白和古菌鞭毛蛋白最初都是带有IV型菌毛蛋白样信号肽的前体蛋白，必须由一种类前菌毛蛋白酶的酶将其去除。这种酶对于古菌鞭毛蛋白来说是FlaK，对于菌毛蛋白来说是EppA。此外，菌毛蛋白和古菌鞭毛蛋白都用N - 连接聚糖进行修饰。古菌鞭毛蛋白具有一个N - 连接的四糖，而菌毛蛋白有一个五糖，它由古菌鞭毛蛋白的四糖组成，但在连接糖上还连接有一个额外的糖，一种未鉴定的己糖。在本报告中，我们表明古菌鞭毛蛋白在没有N - 糖基化的情况下也能被FlaK加工，并且N - 糖基化可以发生在仍保留其信号肽的古菌鞭毛蛋白上。相比之下，菌毛蛋白除非被EppA作用去除信号肽，否则不会被糖基化。然而，EppA仍然可以从非糖基化的菌毛蛋白上去除信号肽。这些发现表明，尽管菌毛蛋白和古菌鞭毛蛋白都是类IV型菌毛蛋白，但它们翻译后修饰的顺序存在差异。
