Crystalline bacterial cell surface layers

Summary Crystalline arrays of proteinaceous subunits forming surface layers (S‐layers) are one of the most commonly observed prokaryotic cell envelope structures. They are ubiquitous amongst Gram‐positive and Gram‐negative archaeobacteria and eubacteria and, if present, account for the major protein species produced by the cells. S‐layers can provide organisms with a selection advantage by providing various functions including protective coats, molecular sieves, ion traps and structures involved in cell surface interactions. S‐layers were identified as contributing to virulence when present as a structural component of pathogens. In Gram‐negative archaeobacteria they are involved in determining cell shape and cell division. The crystalline arrays reveal a broad‐application potential in biotechnology, vaccine development and molecular nanotechnology.