S-Layer Glycoproteins and Flagellins: Reporters of Archaeal Posttranslational Modifications

Abstract

Many archaeal proteins undergo posttranslational modifications. S-layer proteins and flagellins have been used successfully to study a variety of these modifications, including N-linked glycosylation, signal peptide removal and lipid modification. Use of these well-characterized reporter proteins in the genetically tractable model organisms, Haloferax volcanii, Methanococcus voltae and Methanococcus maripaludis, has allowed dissection of the pathways and characterization of many of the enzymes responsible for these modifications. Such studies have identified archaeal-specific variations in signal peptidase activity not found in the other domains of life, as well as the enzymes responsible for assembly and biosynthesis of novel N-linked glycans. In vitro assays for some of these enzymes have already been developed. N-linked glycosylation is not essential for either Hfx. volcanii or the Methanococcus species, an observation that allowed researchers to analyze the role played by glycosylation in the function of both S-layers and flagellins, by generating mutants possessing these reporters with only partial attached glycans or lacking glycan altogether. In future studies, it will be possible to consider questions related to the heterogeneity associated with given modifications, such as differential or modulated glycosylation.

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).…”

“…volcanii and S. acidocaldarius, the S-layer glycoprotein has been used extensively as the model reporter of N-glycosylation (6,107,118,222). This protein is particularly important in Archaea, as opposed to Bacteria, since most Archaea, including these two organisms (63,223), have a cell envelope consisting solely of an S-layer overlying a cytoplasmic membrane without the benefit of an intermediate peptidoglycan equivalent, a situation never found in S-layer-bearing Bacteria (224,225).…”

Flagellar Glycosylation: Current Advances

“…A deletion mutant analysis of three glycosyltransferases and an oligosaccharyltransferase (Stt3p homologue) from M. maripaludis revealed that these genes were responsible for flagellin glycosylation supported by the fact that glycan reduced flagellins were not assembled into the flagella filament . The structural and genetic analysis of archaeal flagellin glycosylation is frequently linked with S-layer protein glycosylation, and the reader is referred to a recent detailed review (Jarrell et al, 2010).…”

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

“…-linked glycosylation of proteins is a posttranslational modification found in all three domains of life (12,23,43). While its distribution is apparently rather limited throughout the domain Bacteria, N-linked glycosylation is widespread in the Archaea.…”