As for many bacteria the S-layer represents the outermost interaction zone with their respective environment, its functions are very diverse and vary from species to species. In Gram-negative archaea the S-layer is the only cell wall component and therefore is important for mechanical stabilisation. Additional functions associated with S-layers include:
- protection against bacteriophages and phagocytosis
- resistance against low pH
- barrier against high molecular weight substances (e.g. lytic enzymes)
- adhesion (for glycosylated S-layers)
- stabilisation of the membrane
- provide adhesion sites for exoproteins
- provide a periplasmic compartment in Gram-positive prokaryotes together with the peptidoglycan and the
- cytoplasmic membrane
