Sweet New Roles for Protein Glycosylation in Prokaryotes

Long-held to be a post-translational modification unique to Eukarya, it is now clear that both Bacteria and Archaea also perform protein glycosylation, namely the covalent attachment of mono- to polysaccharides to specific protein targets. At the same time, many of the roles assigned to this protein-processing event in eukaryotes, such as guiding protein folding/quality control, intracellular trafficking, dictating cellular recognition events and others, do not apply or are even irrelevant to prokaryotes. As such, protein glycosylation must serve novel functions in Bacteria and Archaea. Recent efforts have begun to elucidate some of these prokaryote-specific roles, which are addressed in this review. Because many of the roles assumed by protein glycosylation in eukaryotes are not applicable to Bacteria or Archaea, this postmodification likely serves distinct roles in prokaryotes. In Bacteria, protein glycosylation systems are found in nonpathogenic species, pointing to roles beyond virulence. In Bacteria and Archaea, protein glycosylation contributes to the integrity and proper architecture of glycoprotein-containing assemblies. Changes in protein glycosylation offers prokaryotes a rapid and reversible manner in which to respond to environmental changes.