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.

Figure 1

Immunoblot of wild-type M. maripaludis cells and mutants carrying deletions in various agl genes. Blots were developed with anti-flagellin antisera. Blot shows almost quantitative transfer of truncated glycans occurs.

Figure 2

Structures of N-linked glycans in various Archaea.

Figure 3

Stage of action of various glycosyltransferases and oligosaccharyltransferase in the N-linked glycan assembly of Haloferax volcanii, Methanococcus maripaludis, and Methanococcus voltae.

Figure 4

Model of assembly of M. maripaludis flagella, incorporating glycan synthesis and signal peptide removal.