BIOCHEMISTRY OF S-LAYERS

During evolution prokaryotes have developed different envelope structu res exterior to the cell wall proper. Among these surface components a re regularly arranged S-layers and capsules. The structural characteri zation and the detailed chemical analysis of these surface molecules i s a prerequisite to understand their biosynthesis and functional role( s) at the molecular level. Of particular interest are the glycosylated S-layer proteins which belong to the first prokaryotic glycoproteins ever described. Their characterization was performed on strains belong ing to the thermophilic Bacillaceae and included structural studies an d experiments to learn about the pathways for the glycan biosynthesis of S-layer glycoproteins. As an example for non-glycosylated S-layer p roteins those of Lactobacillus helveticus strains are described in det ail. Recently, a novel type of bacterial glycoconjugate was observed i n the cell envelope of the extremely halophilic archaeon Natronococcus occultus which consists of a glycosylated polyglutamyl polymer. Besid e the conventional biochemical techniques for the analysis new sophist icated instrumental methods such as X-ray photoelectron spectroscopy a nd matrix-assisted laser desorption ionization or electrospray ionizat ion mass spectrometry have been introduced for the analysis of the pro tein and glycan portions of these cell surface macromolecules.