Biogenesis and functions of bacterial S-layers

• Published in: Nature reviews. Microbiology Vol. 12; no. 3; pp. 211 - 222
• Main Authors: Fagan, Robert P., Fairweather, Neil F.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.03.2014; Nature Publishing Group
• Subjects: 631/326/41/1969; 631/326/41/2180; 631/326/41/2536; 631/326/88; Animals; Archaea; Archaea - genetics; Archaea - metabolism; Arrays; Bacteria; Bacteria - genetics; Bacteria - metabolism; Bacterial proteins; Biosynthesis; Cell culture; Cell division; Cell research; Cell survival; Cell Wall - metabolism; Cell walls; Cellular control mechanisms; Crystallography; Crystals; Effector cells; Fetuses; Functionals; Genes; Genetic analysis; Genetic diversity; Genetic Variation; Genomics; Glycan; Glycosylation; Gram-positive bacteria; Humans; Immune system; Infectious Diseases; Life Sciences; Medical Microbiology; Membrane Glycoproteins - genetics; Membrane Glycoproteins - metabolism; Membrane Glycoproteins - secretion; Microbiology; Microscopy; Models, Biological; Morphology; Multigene Family - physiology; Parasitology; Pathogens; Properties; Protein arrays; Protein biosynthesis; Protein Structure, Tertiary; Proteins; review-article; Structural analysis; Structure-function relationships; Surface layers; Survival; Swimming; Two dimensional analysis; Virology; United Kingdom > UK
• ISSN: 1740-1526; 1740-1534; 1740-1534
• DOI: 10.1038/nrmicro3213

Key Points S-layers are two-dimensional (2D) protein arrays that are frequently found on the surface of bacteria and archaea. Genetic analysis reveals a wide diversity of genes that encode S-layer proteins (SLPs) in some species, and several mechanisms are found to facilitate gene switching and regulation. Secretion of S-layer proteins often involves a dedicated secretion system, such as accessory Sec systems in Bacillus anthracis and Clostridium difficile , and a wide range of mechanisms for anchoring S-layers to the underlying cell envelope have been identified. Gram-positive species, including B. anthracis and C. difficile , possess large families of genes encoding proteins that are related to the S-layer protein and that share a common anchoring mechanism. In many species, the SLPs are glycosylated. Dedicated glycosylation loci are found that specify all the genes that are necessary for the synthesis of glycan, its secretion across the membrane and ligation to the SLP via N- or O- linkages. S-layers have been the subject of intensive structural analysis since their identification in the 1950s. Recent efforts are gradually improving our high-resolution structural knowledge of various S-layer proteins and finally enabling reasonable quality models of an entire S-layer to be made. SLPs have evolved to mediate a broad range of functions, including biogenesis of the cell wall, control of cell division and specialized activities, such as swimming. In pathogens, SLPs can interfere with the immune system and can aid survival via adhesion to host cells. In Gram-positive bacteria, functions are often associated with an effector domain that can confer properties that are distinct from the ability to form a 2D array. Paracrystalline arrays of proteins decorate the surface of many bacteria. In this Review, Fagan and Fairweather discuss recent insights into the structural and functional properties of these surface layers, which are beginning to reveal their importance for the growth and survival of many species. The outer surface of many archaea and bacteria is coated with a proteinaceous surface layer (known as an S-layer), which is formed by the self-assembly of monomeric proteins into a regularly spaced, two-dimensional array. Bacteria possess dedicated pathways for the secretion and anchoring of the S-layer to the cell wall, and some Gram-positive species have large S-layer-associated gene families. S-layers have important roles in growth and survival, and their many functions include the maintenance of cell integrity, enzyme display and, in pathogens and commensals, interaction with the host and its immune system. In this Review, we discuss our current knowledge of S-layer and related proteins, including their structures, mechanisms of secretion and anchoring and their diverse functions.