%0 Journal Article
%T Biosynthesis and Role of N-Linked Glycosylation in Cell Surface Structures of Archaea with a Focus on Flagella and S Layers
%A Ken F. Jarrell
%A Gareth M. Jones
%A Divya B. Nair
%J International Journal of Microbiology
%D 2010
%I Hindawi Publishing Corporation
%R 10.1155/2010/470138
%X 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. 1. Introduction N-linked glycosylation is one of the most common posttranslational modifications found on proteins in eukaryotic cells [1] and has now been documented in both prokaryotic domains as well [2, 3]. Searches of complete genome sequences can readily identify homologues to the oligosaccharyltransferase STT3 subunit that transfers the assembled glycan from a lipid carrier to the target motif (amide linkage to asparagine within the sequon N-X-S/T) on the protein. This gene would be required in all organisms where N-linked glycosylation occurs and is readily found in eukarya and a limited number of bacteria but in almost all sequenced archaeal genomes. Of greater than 50 completed archaeal genomes, only 2 appear to lack this gene (Aeropyrum pernix and Methanopyrus kandleri) [4], suggesting that this posttranslational modification is much more common in archaea than in bacteria. Indeed, while many glycans associated with S layers in Bacteria have been reported, all are exclusively O-linked [5]. In Archaea, where glycosylation of S layers is more common than in Bacteria, most glycan linkages are of the N variety [6], although S layers containing glycans attached by both O and N linkage occur [7]. Extremely little is known of the O-linked process in Archaea. In Archaea, N-linked glycosylation is most commonly found on S layer proteins [3, 6, 8¨C12] and flagellins [7, 9, 10, 13, 14] and,
%U http://www.hindawi.com/journals/ijmicro/2010/470138/