Studies on archaebacterial S-layers

Abstract

The S-layers of Methanococcus vannielii, Methanococcus thermolithotropbicus and Methanococcus jannaschii , organisms exhibiting optimal growth at temperature conditions ranging from the mesophilic to the extremely thermophilic, are composed of hexagonally arranged protein subunits of different molecular weights. Glycosylated proteins were not found to be present. The amino acid compositions of the main S-layer proteins of these species were not significantly different. Non-polar amino acids were predominant in the acidic proteins. The cell envelope of the aggregate-forming methanogen Methanolobus tindarius consists of hexagonally arranged subunits exhibiting a center-to-center distance of 12 nm. The largest periodate-Schiff positive envelope protein, which has a molecular weight of 156000, was isolated. It is composed of 23 mol% acidic, 12 mol% basic, 17 mol% polar and 48 mol% nonpolar amino acids. In contrast to the corresponding protein isolated from the methanococci, this protein contains about 3.0% (w/v) carbohydrate. As revealed by immunological studies incorporating ferritin-labeling, the protein is located on the cell surface and is probably involved in cell-cell adhesion. The S-layer of Thermoproteus tenax and the striated sheath-like S-layer of Methanothrix soehngenii possess considerable resistance to sodium dodecyl sulfate. These layers are composed of amino acids and neutral sugars. Amino sugars were additionally found in the case of Thermoproteus tenax . The S-layers of Sulfolobus soifataricus and Sulfolobus brierieyi disintegrate in SDS solution at 60 °C. This is not the case with the corresponding structure from Sulfolobus acidocaldarius . Immunoenzymatic analysis revealed a low degree of relatedness between the S-layers of Sulfolobus acidocaldarius and Sulfolobus soifataricus , but Sulfolobus brierieyi shows no antigenic relationship to either of these species in this regard.