Department of Life Sciences, Ben Gurion University of the Negev Beersheva, Israel.
Front Microbiol. 2013 Dec 24;4:403. doi: 10.3389/fmicb.2013.00403.
Long believed to be restricted to Eukarya, it is now known that cells of all three domains of life perform N-glycosylation, the covalent attachment of glycans to select target protein asparagine residues. Still, it is only in the last decade that pathways of N-glycosylation in Archaea have been delineated. In the haloarchaeon Haloferax volcanii, a series of Agl (archaeal glycosylation) proteins is responsible for the addition of an N-linked pentasaccharide to modified proteins, including the surface (S)-layer glycoprotein, the sole component of the surface layer surrounding the cell. The S-layer glycoprotein N-linked glycosylation profile changes, however, as a function of surrounding salinity. Upon growth at different salt concentrations, the S-layer glycoprotein is either decorated by the N-linked pentasaccharide introduced above or by both this pentasaccharide as well as a tetrasaccharide of distinct composition. Recent efforts have identified Agl5-Agl15 as components of a second Hfx. volcanii N-glycosylation pathway responsible for generating the tetrasaccharide attached to S-layer glycoprotein when growth occurs in 1.75 M but not 3.4 M NaCl-containing medium.
长期以来，人们一直认为 N-糖基化是真核生物所特有的，现在人们已经知道，所有三个生命领域的细胞都能进行 N-糖基化，即将聚糖共价连接到选定的靶蛋白天冬酰胺残基上。尽管如此，直到最近十年，古菌中的 N-糖基化途径才被描绘出来。在产甲烷菌 Haloferax volcanii 中，一系列 Agl（古菌糖基化）蛋白负责将 N-连接的五糖添加到修饰蛋白上，包括表面（S）层糖蛋白，这是细胞周围表面层的唯一成分。然而，S-层糖蛋白的 N-连接糖基化谱会随着周围盐度的变化而变化。在不同盐浓度下生长时，S-层糖蛋白要么被上述 N-连接的五糖修饰，要么被这种五糖以及组成不同的四糖修饰。最近的研究努力已经确定了 Agl5-Agl15 是第二个 Hfx. volcanii N-糖基化途径的组成部分，当在含有 1.75 M 但不含 3.4 M NaCl 的培养基中生长时，该途径负责生成与 S-层糖蛋白相连的四糖。
