Archaeal Cell Walls

Next to the bacterial and eukaryal domains, Archaea form the third domain of life. One major difference to bacteria is the composition of the cell wall. The cell wall of most Archaea is formed by a proteinaceous surface (S-) layer. S-layer proteins have the intrinsic ability to form two-dimensional crystals, which can have an oblique (p2), square (p4) or hexagonal (p3 or p6) symmetry. All currently studied archaeal S-layer proteins were found to be modified by the attachment of N-linked and, in some cases, additionally by O-linked glycans. Next to the S-layer (glyco-)proteins, sugar polymers like pseudomurein, methanochondroitin or heteropolysaccharides are also found in archaeal cell walls. These polymeric cell wall structures can either form the sole cell wall structure or be supported by an additional S-layer cover. A few archaeal species even completely lack a cell wall. Key Concepts: Archaeal cell envelopes lack murein or a lipopolysaccharide (LPS)-containing outer membrane. Most Archaea posses a glycosylated proteinaceous surface layer (S-layer) as their sole cell wall structure. In some Archaea, the cell wall is composed of glycan polymers, like glutaminylglycan, heterosaccharide, methanochondroitin or pseudomurein. Keywords: archaea; cell envelope; glutaminylglycan; glycosylation; heteropolysaccharide; methanochondroitin; pseudomurein; S-layer (glyco-)protein