Kaminski Lina, Guan Ziqiang, Abu-Qarn Mehtap, Konrad Zvia, Eichler Jerry
Department of Life Sciences, Ben Gurion University of the Negev, Beersheva 84105, Israel.
Biochim Biophys Acta. 2012 Oct;1820(10):1664-70. doi: 10.1016/j.bbagen.2012.06.014. Epub 2012 Jun 27.
Recent studies of Haloferax volcanii have begun to elucidate the steps of N-glycosylation in Archaea, where this universal post-translational modification remains poorly described. In Hfx. volcanii, a series of Agl proteins catalyzes the assembly and attachment of a N-linked pentasaccharide to the S-layer glycoprotein. Although roles have been assigned to the majority of Agl proteins, others await description. In the following, the contribution of AglR to N-glycosylation was addressed.
A combination of bioinformatics, gene deletion, mass spectrometry and metabolic radiolabeling served to show a role for AglR in archaeal N-glycosylation at both the dolichol phosphate and reporter glycoprotein levels.
The modified behavior of the S-layer glycoprotein isolated from cells lacking AglR points to an involvement of this protein in N-glycosylation. In cells lacking AglR, glycan-charged dolichol phosphate, including mannose-charged dolichol phosphate, accumulates. At the same time, the S-layer glycoprotein does not incorporate mannose, the final subunit of the N-linked pentasaccharide decorating this protein. AglR is a homologue of Wzx proteins, annotated as flippases responsible for delivering lipid-linked O-antigen precursor oligosaccharides across the bacterial plasma membrane during lipopolysaccharide biogenesis.
The effects resulting from aglR deletion are consistent with AglR interacting with dolichol phosphate-mannose, possibly acting as a dolichol phosphate-mannose flippase or contributing to such activity.
Little is known of how lipid-linked oligosaccharides are translocated across membrane during N-glycosylation. The possibility of Hfx. volcanii AglR mediating or contributing to flippase activity could help address this situation.
最近对嗜盐栖热袍菌（Haloferax volcanii）的研究已开始阐明古菌中N-糖基化的步骤，而这种普遍的翻译后修饰在古菌中仍描述甚少。在嗜盐栖热袍菌中，一系列Agl蛋白催化N-连接五糖组装并连接到S层糖蛋白上。虽然大多数Agl蛋白的作用已明确，但其他蛋白的作用仍有待描述。以下研究了AglR对N-糖基化的作用。
综合运用生物信息学、基因缺失、质谱分析和代谢性放射性标记技术，以揭示AglR在磷酸多萜醇和报告糖蛋白水平上对古菌N-糖基化的作用。
从缺乏AglR的细胞中分离出的S层糖蛋白的修饰行为表明该蛋白参与N-糖基化。在缺乏AglR的细胞中，带聚糖的磷酸多萜醇，包括带甘露糖的磷酸多萜醇会积累。与此同时，S层糖蛋白不掺入甘露糖，而甘露糖是修饰该蛋白的N-连接五糖的最后一个亚基。AglR是Wzx蛋白的同源物，在脂多糖生物合成过程中，Wzx蛋白被认为是负责将脂质连接的O抗原前体寡糖转运穿过细菌质膜的翻转酶。
缺失aglR所产生的影响与AglR与磷酸多萜醇 - 甘露糖相互作用一致，可能作为磷酸多萜醇 - 甘露糖翻转酶或促进这种活性。
关于脂质连接的寡糖在N-糖基化过程中如何跨膜转运知之甚少。嗜盐栖热袍菌AglR介导或促进翻转酶活性的可能性有助于解决这一问题。
