Bacterial and archaeal S-layers as object of bionanotechnology

Many species of Bacteria and Archaea posses a regularly structured surface layers (S-layers) as outermost cell envelope component. S-layers composed of a single protein or glycoprotein species. The individual subunits of S-layers interact with each other and with the supporting bacterial envelope component through non-covalent forces. Pores in the crystalline protein network are with mean diameter of 2-6 nm, the thickness of S-layer is 5-10 nm. The isolated S-layer subunits reassemble into two-dimensional crystalline arrays in solution, on solid supports, on planar lipid films. These unique features of S-layers have led to a broad spectrum applications. This review focuses on the structural properties S-layers and S-proteins and their applications with accent to using this structures in nanobiotechnology.     

细菌表面S-层的结构及其功能和应用前景

细菌的细胞外壁一般由细胞壁和细胞膜组成,除此之外,在许多古细菌和真细菌中还有一层表面结构,称为表面层(Surface layers)或称为S-层(S-layers),它们是由蛋白质组成的晶格状结构,位于细胞壁或细胞膜外层,是生物进化过程中最简单的一种生物膜[1,2].     

S-layers as a tool kit for nanobiotechnological applications

Crystalline bacterial cell surface layers (S-layers) have been identified in a great number of different species of bacteria and represent an almost universal feature of archaea. Isolated native S-layer proteins and S-layer fusion proteins incorporating functional sequences self-assemble into monomolecular crystalline arrays in suspension, on a great variety of solid substrates and on various lipid structures including planar membranes and liposomes. S-layers have proven to be particularly suited as building blocks and patterning elements in a biomolecular construction kit involving all major classes of biological molecules (proteins, lipids, glycans, nucleic acids and combinations of them) enabling innovative approaches for the controlled 'bottom-up' assembly of functional supramolecular structures and devices. Here, we review the basic principles of S-layer proteins and the application potential of S-layers in nanobiotechnology and biomimetics including life and nonlife sciences.     

Two-dimensional protein crystals (S-layers): Fundamentals and applications

Two-diminsional crystalline surface layers (S-layers) composed of prtein or glucoprotein subunits are one of the most commonly observed prokaryotic cell envelope structures. lsolated S-layer Subunits are endowed with the ability to assemble into monomolecular arrays in suspension, on surfaces or interface by an entropy-driven process. S-layer lattices are isoporous structures with functional groups located on the surface in an identical position and orientation. These characteristic featupes have alreadu led to applicatioinns of S-layers as (1) ultrafilration membranes with well-defiled mmlecular weight cut -ooffs and excellent antifouling characteristics, (2) immobilization matrices for functional molecules as required for affiviy and enzyme memberanes, affiniy micricarriers and biosensors, (3) conjugate vaaines, (4) carriers for Langmuir-Blodgett films and reconstituted biological memberanes, and (5) patterning elements in molecular nanotechnology.     

Mechanism of osmoprotection by archaeal S-layers: a theoretical study

Many Archaea possess protein surface layers (S-layers) as the sole cell wall component. S-layers must therefore integrate the basic functions of mechanical and osmotic cell stabilisation. While the necessity is intuitively clear, the mechanism of structural osmoprotection by S-layers has not been elucidated yet. The theoretical analysis of a model S-layer-membrane assembly, derived from the typical cell envelope of Crenarchaeota, explains how S-layers impart lipid membranes with increased resistance to internal osmotic pressure and offers a quantitative assessment of S-layer stability. These considerations reveal the functional significance of S-layer symmetry and unit cell size and shed light on the rationale of S-layer architectures.     

Structural and chemical characterization of S-layers of selected strains ofBacillus stearothermophilus andDesulfotomaculum nigrificans

The structures, amino acid- and neutral sugar compositions of the crystalline surface layers (S-layers) of four selected strains each ofBacillus stearothermophilus andDesulfotomaculum nigrificans were compared. Among the four strains of each species a remarkable diversity in the molecular weights of the S-layer subunits and in the geometry and constants of the S-layer lattices was apparent. The crystalline arrays included hexagonal (p6), square (p4) and oblique (p2) lattices. In vitro self-assembly of isolated S-layer subunits (or S-layer fragments) led to the formation of flat sheets or open-ended cylindrical assembly products. The amino acid composition of the S-layers exhibited great similarities and was predominantly acidic. With the exception of the S-layers of two strains ofB. stearothermophilus (where only traces of neutral sugars could be detected), all other S-layer proteins seemed to be glycosylated. Among these strains significant differences in the amount and composition of the glycan portions were found. Based on this diversity interesting questions may be asked about the biological significance of the carbohydrate units of glycoproteins in prokaryotic organisms.     

Bacterial nitrite-reducing enzymes.

The enzymic reduction of nitrite takes place in a wide range of bacteria and is found to occur in denitrifying, assimilatory and dissimilatory pathways. In this review we describe the major molecular characteristics of the various enzymes employed in each of these processes.     

Bacterial phospholipases C.

A variety of pathogenic bacteria produce phospholipases C, and since the discovery in 1944 that a bacterial toxin (Clostridium perfringens alpha-toxin) possessed an enzymatic activity, there has been considerable interest in this class of proteins. Initial speculation that all phospholipases C would have lethal properties has not been substantiated. Most of the characterized enzymes fall into one of four groups of structurally related proteins: the zinc-metallophospholipases C, the sphingomyelinases, the phosphatidylinositol-hydrolyzing enzymes, and the pseudomonad phospholipases C. The zinc-metallophospholipases C have been most intensively studied, and lethal toxins within this group possess an additional domain. The toxic phospholipases C can interact with eukaryotic cell membranes and hydrolyze phosphatidylcholine and sphingomyelin, leading to cell lysis. However, measurement of the cytolytic potential or lethality of phospholipases C may not accurately indicate their roles in the pathogenesis of disease. Subcytolytic concentrations of phospholipase C can perturb host cells by activating the arachidonic acid cascade or protein kinase C. Nonlethal phospholipases C, such as the Listeria monocytogenes PLC-A, appear to enhance the release of the organism from the host cell phagosome. Since some phospholipases C play important roles in the pathogenesis of disease, they could form components of vaccines. A greater understanding of the modes of action and structure-function relationships of phospholipases C will facilitate the interpretation of studies in which these enzymes are used as membrane probes and will enhance the use of these proteins as models for eukaryotic phospholipases C.     

Bacterial phospholipases C.

A variety of pathogenic bacteria produce phospholipases C, and since the discovery in 1944 that a bacterial toxin (Clostridium perfringens alpha-toxin) possessed an enzymatic activity, there has been considerable interest in this class of proteins. Initial speculation that all phospholipases C would have lethal properties has not been substantiated. Most of the characterized enzymes fall into one of four groups of structurally related proteins: the zinc-metallophospholipases C, the sphingomyelinases, the phosphatidylinositol-hydrolyzing enzymes, and the pseudomonad phospholipases C. The zinc-metallophospholipases C have been most intensively studied, and lethal toxins within this group possess an additional domain. The toxic phospholipases C can interact with eukaryotic cell membranes and hydrolyze phosphatidylcholine and sphingomyelin, leading to cell lysis. However, measurement of the cytolytic potential or lethality of phospholipases C may not accurately indicate their roles in the pathogenesis of disease. Subcytolytic concentrations of phospholipase C can perturb host cells by activating the arachidonic acid cascade or protein kinase C. Nonlethal phospholipases C, such as the Listeria monocytogenes PLC-A, appear to enhance the release of the organism from the host cell phagosome. Since some phospholipases C play important roles in the pathogenesis of disease, they could form components of vaccines. A greater understanding of the modes of action and structure-function relationships of phospholipases C will facilitate the interpretation of studies in which these enzymes are used as membrane probes and will enhance the use of these proteins as models for eukaryotic phospholipases C.     

Bacterial tracheitis in children.

We examined the records of 14 patients aged 7 months to 10 1/4 years who were treated for bacterial tracheitis from May 1982 to December 1987; the management protocol for 13 of the patients included the use of nasotracheal intubation. The infection was caused by Staphylococcus aureus in seven, Haemophilus influenzae in three, Branhamella catarrhalis in one and Streptococcus pneumoniae in one. Both H. influenzae and B. catarrhalis were isolated in another patient, and no organism was found in the remaining patient. In addition to the bacteria, viruses were cultured from the tracheal secretions of two patients. The mean duration of intubation was 7.6 days and of hospital stay 9.2 days. Twelve of the cases occurred during the cold months of the year (October to March). Of the three deaths only one occurred in the pediatric intensive care unit and was due to severe bronchospasm and an air leak that caused bilateral pneumothorax and pneumomediastinum. In one patient subglottic stenosis developed that necessitated tracheostomy. Healing began 5 to 9 days after the onset of symptoms, as demonstrated with the use of repeated fibreoptic bronchoscopy. We found that the airway could be safely managed with the use of a nasotracheal tube. Bronchoscopy helped to confirm the diagnosis, to remove adherent secretions and to monitor the course of the disease. The ventilation tube can be removed after the patient''s temperature returns to normal, if there is an air leak around the tube, if the quantity and viscosity of the secretions decrease and if healing is observed at bronchoscopy.