Biosynthesis and Role of N-Linked Glycosylation in Cell Surface Structures of Archaea with a Focus on Flagella and S Layers

Abstract

The genetics and biochemistry of the N-linked glycosylation system of Archaea have been investigated over the past 5 years using flagellins and S layers as reporter proteins in the model organisms, Methanococcus voltae, Methanococcus maripaludis, and Haloferax volcanii. Structures of archaeal N-linked glycans have indicated a variety of linking sugars as well as unique sugar components. In M. voltae, M. maripaludis, and H. volcanii, a number of archaeal glycosylation genes (agl) have been identified by deletion and complementation studies. These include many of the glycosyltransferases and the oligosaccharyltransferase needed to assemble the glycans as well as some of the genes encoding enzymes required for the biosynthesis of the sugars themselves. The N-linked glycosylation system is not essential for any of M. voltae, M. maripaludis, or H. volcanii, as demonstrated by the successful isolation of mutants carrying deletions in the oligosaccharyltransferase gene aglB (a homologue of the eukaryotic Stt3 subunit of the oligosaccharyltransferase complex). However, mutations that affect the glycan structure have serious effects on both flagellation and S layer function.

Identification of Genes Involved in the Acetamidino Group Modification of the Flagellin N-Linked Glycan of Methanococcus maripaludis

“…The N-linked glycosylation process in archaea is thought to be similar to that reported for bacteria (3,22,43), where the glycan is first assembled on a lipid carrier on the cytoplasmic side of the cytoplasmic membrane. However, archaea use dolichol mono-or pyrophosphate as the lipid carrier (like eukaryotes), while bacteria use undecaprenol pyrophosphate (18,19,31).…”

Archaeosortases and Exosortases Are Widely Distributed Systems Linking Membrane Transit with Posttranslational Modification

“…This is a subfamily of AglB (archaeal glycosylation B) (18), a homolog of the oligosaccharyltransferase complex STT3 subunit from the endoplasmic reticulum of eukaryotes, and is defined by model TIGR04154. Because of the apparent monophyly of the PGF-CTERM-encoding species, BLAST cutoffs can be chosen to select proteins from exactly that species list, for an average of 30 (but as few as 6) proteins per genome.…”

“…Its HMM produces sharply lower scores for even the top-scoring homolog outside this set of genomes. Many proteins with PGF-CTERM regions, such as S-layer glycoproteins, are known or thought to be targets of N-glycosylation involving AglB (18).…”

N-Linked Glycosylation in Archaea: a Structural, Functional, and Genetic Analysis

“…Our current understanding of N-glycosylation in the methanogens has come from a significant body of work addressing the structure and genetics of this PTM in two species of Methanococcus, namely, M. voltae and M. maripaludis (104)(105)(106)(107). In addition, in vitro biochemical work using purified enzymes has further con-tributed to our understanding of the process in this group of Archaea (108)(109)(110).…”