Agl28 and Agl29 are key components of a Halobacterium salinarum N-glycosylation pathway

Two key components of a pathway used for N-glycosylation in the halophilic archaea Halobacterium salinarum are described. Although Halobacterim salinarum provided the first example of N-glycosylation outside the Eukarya, only recently has attention focused on delineating the pathway responsible for the assembly of the N-linked tetrasaccharide decorating selected proteins in this haloarchaeon. In the present report, the roles of VNG1053G and VNG1054G, two proteins encoded by genes clustered together with a set of genes demonstrated to encode N-glycosylation pathway components, were considered. Relying on both bioinformatics and gene deletion and subsequent mass spectrometry analysis of known N-glycosylated proteins, VNG1053G was determined to be the glycosyltransferase responsible for addition of the linking glucose, while VNG1054G was deemed to be the flippase that translocates the lipid-bound tetrasaccharide across the plasma membrane to face the cell exterior, or to contribute to such activity. As observed with Hbt. salinarum lacking other components of the N-glycosylation machinery, both cell growth and motility were compromised in the absence of VNG1053G or VNG1054G. Thus, given their demonstrated roles in Hbt. salinarum N-glycosylation, VNG1053G and VNG1054G were re-annotated as Agl28 and Agl29, according to the nomenclature used to define archaeal N-glycosylation pathway components.

Automated summary

This article describes two key components of the N-glycosylation pathway in the halophilic archaea Halobacterium salinarum. The roles of VNG1053G and VNG1054G, two proteins encoded by genes clustered together with a set of genes demonstrated to encode N-glycosylation pathway components, were investigated. It was determined that VNG1053G is the glycosyltransferase responsible for adding the linking glucose, while VNG1054G is the flippase that translocates the lipid-bound tetrasaccharide across the plasma membrane. The absence of VNG1053G or VNG1054G compromises cell growth and motility in Hbt. salinarum, highlighting their importance in N-glycosylation.