Long believed to be restricted to Eukarya, it is now clear that cells of all three domains of life perform N-glycosylation, namely the covalent attachment of glycans to select target protein asparagine residues. Yet, while N-glycosylation is apparently restricted to a limited sub-population of Bacteria, almost all Archaea possess the ability for such protein processing. Still, it is only in the last decade that pathways of N-glycosylation in Archaea have been delineated. In the haloarchaeon Haloferax volcanii originally isolated from the Dead Sea, a series of Agl (archaeal glycosylation) proteins is responsible for the addition of an N-linked pentasaccharide to modified proteins, including the surface (S)-layer glycoprotein, the sole component of the S-layer surrounding the cell. The N-linked glycosylation profile of the Hfx. volcanii S-layer glycoprotein changes, however, as a function of surrounding salinity. Depending on environmental salt concentrations, the S-layer glycoprotein is either decorated by the N-linked pentasaccharide introduced above or by both this pentasaccharide as well as a tetrasaccharide of distinct composition. Accordingly, the components of a second Hfx. volcanii N-glycosylation pathway responsible for generating the tetrasaccharide attached to the S-layer glycoprotein when growth occurs in 1.75 M but not 3.4 M NaCl-containing medium have been identified. In my talk, these and other recents findings related to Hfx. volcanii N-glycosylation will be addressed.
