MOLECULAR-BIOLOGY OF S-LAYERS

In this chapter we report on the molecular biology of crystalline surf ace layers of different bacterial groups. The limited information indi cates that there are many variations on a common theme. Sequence varie ty, antigenic diversity, gene expression, rearrangements, influence of environmental factors and applied aspects are addressed. There is con siderable variety in the S-layer composition, which was elucidated by sequence analysis of the corresponding genes. In Corynebacterium gluta micum one major cell wall protein is responsible for the formation of a highly ordered, hexagonal array. In contrast, two abundant surface p roteins form the S-layer of Bacillus anthracis. Each protein possesses three S-layer homology motifs and one protein could be a virulence fa ctor. The antigenic diversity and ABC transporters are important featu res, which have been studied in methanogenic archaea. The expression o f the S-layer components is controlled by three genes in the case of T hermus thermophilus. One has repressor activity on the S-layer gene pr omoter, the second codes for the S-layer protein. The rearrangement by reciprocal recombination was investigated in Campylobacter fetus. 7-8 S-layer proteins with a high degree of homology at the 5' and 3' ends were found. Environmental changes influence the surface properties of Bacillus stearothermophilus. Depending on oxygen supply, this species produces different S-layer proteins. Finally, the molecular bases for some applications are discussed. Recombinant S-layer fusion proteins have been designed for biotechnology.