6533b7d9fe1ef96bd126d5c8

RESEARCH PRODUCT

Proteinaceous Surface Layers ofArchaea: Ultrastructure and Biochemistry

subject

description

The cell walls of the Archaea are composed of different polymers such as glutaminylglycan, heterosaccharide, methanochondroitin, pseudomurein, protein, glycoprotein, or glycocalyx. The S-layer glycoprotein of Halobacterium salinarum was the first glycoprotein discovered in bacteria and archaea. Initially, the novel cell wall structures were viewed as curiosities, and their taxonomic significance was not realized until the concept of the Archaea was published. At this time, the results of cell wall studies supported the new view of the phylogeny of the Bacteria and Archaea. Many archaea possess proteinaceous surface layers (S layers), which form two-dimensional regular arrays. The chemical structure of archaeal S-layer glycoproteins has been determined in detail for a few archaeal species, e.g., Methanothermus fervidus, H. salinarum and Haloferax volcanii, and Staphylothermus marinus. The filamentous chains of Methanospirillum hungatei and Methanosaeta concilii (formerly Methanothrix soehngenii) are held together by a proteinaceous fibrillary sheath. The majority of bacterial and archaeal exopolymers are polysaccharides, but exopolymers composed of L-or D-glutamate are also formed. The ultrastructure of N. equitans is similar to many archaea. Future investigations of the unusual symbiosis of these two hyperthermophilic archaea aim at elucidating which proteins of both cell envelopes are directly involved in the physical interaction and in the exchange of metabolites from one cell to the other. The cell envelopes of the Archaea are often directly exposed to extreme environmental conditions, and they cannot be stabilized by cellular factors. S layers represent the most common cell surface layer of Archaea.