Sweet to the extreme: protein glycosylation in Archaea

Abstract

SummaryPost-translational modifications account for much of the biological diversity generated at the proteome level. Of these, glycosylation is the most prevalent. Long thought to be unique to Eukarya, it is now clear that both Bacteria and Archaea are also capable of N-glycosylation, namely the covalent linkage of oligosaccharides to select target asparagine residues. However, while the eukaryal and bacterial Nglycosylation pathways are relatively well defined, little is known of the parallel process in Archaea. Of late, however, major advances have been made in describing the process of archaeal N-glycosylation. Such efforts have shown, as is often the case in archaeal biology, that protein N-glycosylation in Archaea combines particular aspects of the eukaryal and bacterial pathways along with traits unique to this life form. For instance, while the oligosaccharides of archaeal glycoproteins include nucleotideactivated sugars formed by bacterial pathways, the lipid carrier on which such oligosaccharides are assembled is the same as used in eukaryal Nglycosylation. By contrast, transfer of assembled oligosaccharides to their protein targets shows Archaea-specific properties. Finally, addressing N-glycosylation from an archaeal perspective is providing new general insight into this event, as exemplified by the solution of the first crystal structure of an oligosaccharide transferase from an archaeal source.

AglC and AglK Are Involved in Biosynthesis and Attachment of Diacetylated Glucuronic Acid to the N-Glycan in Methanococcus voltae

“…In this system, AglH has been proposed as the glycosyl transferase responsible for the attachment of the linking N-acetylglucosamine (33), while AglA is responsible for the terminal sugar attachment (9). In the moderate halophile Haloferax volcanii, a pentasaccharide is found on the S-layer protein that requires the activities of at least five glycosyl transferases, with AglD, AglE, AglF, AglG, and AglI identified as involved so far (1,3,4,41,42). The next step in the process is to translocate the glycan from the cytoplasmic to the extracellular side of the membrane.…”

A filamentous phage display system for N‐linked glycoproteins

“…Long considered exclusive to eukaryotes, N-linked glycoproteins have now been found in archea 5 and more recently in certain bacteria such as Campylobacter jejuni. 6 In C. jejuni, the genes required for N-linked glycosylation comprise a single 17-kb locus named pgl for protein glycosylation.…”

“…6 In C. jejuni, the genes required for N-linked glycosylation comprise a single 17-kb locus named pgl for protein glycosylation. 7,8 More than 40 periplasmic and membrane glycoproteins have been identified in C. jejuni, 7,9,10 and the N-linked glycan on these proteins is the heptasaccharide GalNAc 5 GlcBac (where Bac is bacillosamine). 10 Similar to the process in eukaryotes, the bacterial glycan is synthesized by sequential addition of nucleotide-activated sugars on a lipid carrier on the cytoplasmic side of the inner membrane 11 and, once assembled, is transferred across the membrane by a flippase enzyme called WlaB.…”

Cellular and organellar membrane-associated proteins in haloarchaea: Perspectives on the physiological significance and biotechnological applications

“…The N-glycosylation sites are scattered throughout the sequence; however, O-glycosylation sites are usually found clustered in a threonine-rich region. At least two of the seven putative N-glycosylation sites of the S-layer glycoprotein in the haloarchaeaon H. volcanii are modified by a pentasaccharide, which comprises a hexose, two hexuronic acids, a methyl ester of hexuronic acid and a mannose [31]. Five glycosyltransferases named AglJ, AglG, AglI, AglE and AglD are sequentially involved in the transfer of five residues to the dolichol phosphate carrier directly or indirectly [3235].…”