AglQ Is a Novel Component of the Haloferax volcanii N-Glycosylation Pathway

Adi Arbiv,Jerry Eichler,Sophie Yurist-Doutsch,Ziqiang Guan,Mario F Feldman

doi:10.1371/journal.pone.0081782

Adi Arbiv, Jerry Eichler + Show 3 more

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https://doi.org/10.1371/journal.pone.0081782

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Journal: PloS one	Publication Date: Nov 13, 2013
Citations: 28	License type: CC BY 3.0

Affiliation: Ben-Gurion University of the Negev, Duke Medical Center

Abstract

N-glycosylation is a post-translational modification performed by members of all three domains of life. Studies on the halophile Haloferax volcanii have offered insight into the archaeal version of this universal protein-processing event. In the present study, AglQ was identified as a novel component of the pathway responsible for the assembly and addition of a pentasaccharide to select Asn residues of Hfx. volcanii glycoproteins, such as the S-layer glycoprotein. In cells deleted of aglQ, both dolichol phosphate, the lipid carrier used in Hfx. volcanii N-glycosylation, and modified S-layer glycoprotein Asn residues only presented the first three pentasaccharide subunits, pointing to a role for AglQ in either preparing the third sugar for attachment of the fourth pentasaccharide subunit or processing the fourth sugar prior to its addition to the lipid-linked trisaccharide. To better define the precise role of AglQ, shown to be a soluble protein, bioinformatics tools were recruited to identify sequence or structural homologs of known function. Site-directed mutagenesis experiments guided by these predictions identified residues important for AglQ function. The results obtained point to AglQ acting as an isomerase in Hfx. volcanii N-glycosylation.

Highlights

The ability of Archaea to perform protein Nglycosylation in Archaea was first reported in 1976 [1], it was only in the last decade that efforts focused on delineating the pathways involved in the archaeal version of this universal post-translational modification, thanks to the development of appropriate molecular tools
In Hfx. volcanii, dolichol phosphate (DolP) serves as the lipid carrier upon which a pentasaccharide N-linked to the S-layer glycoprotein is assembled
The same profile revealed a major peak at the m/z 1055.765, corresponding to a previously described Hfx. volcanii sulfoglycolipid, S-GL-1 [19]. [M-2H]2- ions of the C55 and C60 dolichol phosphate species modified by a hexose and a hexuronic acid (Figure 1C) and by a hexose and two hexuronic acids (Figure 1D) were observed

Summary

Introduction

The ability of Archaea to perform protein Nglycosylation in Archaea was first reported in 1976 [1], it was only in the last decade that efforts focused on delineating the pathways involved in the archaeal version of this universal post-translational modification, thanks to the development of appropriate molecular tools. In Hfx. volcanii, a series of agl (archaeal glycosylation) genes encode proteins involved in the assembly and attachment of a pentasaccharide to select Asn residues of the reporter glycoprotein, the surface (S)-layer glycoprotein. Acting at the cytoplasmic face of the plasma membrane, AglJ, AglG, AglI, AglE sequentially add the first four pentasaccharide residues (i.e. a hexose, two hexuronic acids and the methyl ester of a hexuronic acid) onto a common dolichol phosphate (DolP) carrier, while AglD adds the final pentasaccharide residue, mannose, to a distinct DolP [2,3,4,5,6,7,8]. The terminal pentasaccharide residue, mannose, is transferred from its DolP carrier to the protein-bound tetrasaccharide by the actions of AglS [11]

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