Surface display of antibodies

To screen antibody libraries that contain many millions of different clones, a selection system is required with an efficiency comparable to that of the immune system. This can be achieved by displaying antibodies on the surface of microorganisms containing the antibody's gene, analogous to the expression of the IgM antigen receptor on the surface of unactivated B-lymphocytes. Specific clones can then be selected using immobilized antigens. The minor coat protein of filamentous phages, pIII, which initiates the infection of E.coli by binding to their F-pili, and the major coat protein, pVIII, have been used as carriers for displaying antibodies on the phage surface. Recombinant antibodies have also been targeted to the cell surface of bacteria by fusing them with outer membrane components derived from lipoproteins, OmpA and an IgA protease. However, only the pIII system has been routinely used for screening antibody libraries. Here we describe the various antibody surface display systems and the screening of antibody libraries generated from the gene repertoire of lymphocytes and by gene synthesis. Finally, we have made a short comparison of the bacterial production of Fabs versus single chain antibodies (scFv).     

Surface areas of lipid membranes

Upon photolysis, alkyl pentacyanocobaltate complexes generate alkyl radicals which react rapidly and specifically with nitroxide radicals, and which do not penetrate phospholipid bilayers. By measuring the loss of paramagnetic resonance signal intensity when multilamellar liposomes containing a small amount of spin-labeled lipid are exposed to these radicals, we have measured the proportion of lipid on the external surface of liposomes. We have shown that liposomes prepared under specified conditions from dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine, and binary mixtures of dipalmitoylphosphatidylcholine and cholesterol all have the same proportion of external lipid.     

Surface recognition elements of membrane protein oligomerization

Although certain membrane proteins are functional as monomeric polypeptides, others must assemble into oligomers to carry out their biological roles. High-resolution membrane protein structures provide a valuable resource for examining the sequence features that facilitate-or preclude-assembly of membrane protein monomers into multimeric structures. Here we have utilized a data set of 28 high-resolution alpha-helical membrane protein structures comprising 32 nonredundant polypeptides to address this issue. The lipid-exposed surfaces of membrane proteins that have reached their fully assembled and functional biological units have been compared with those of the individual subunits that build quaternary structures. Though the overall amino acid composition of each set of surfaces is similar, a key distinction-the distribution of small-xxx-small motifs-delineates subunits from membrane proteins that have reached a functioning oligomeric state. Quaternary structure formation may therefore be dictated by small-xxx-small motifs that are not satisfied by intrachain contacts.     

Microbial Etiology of Root Surface Caries

Available knowledge relating to the microbiology of root surface caries was reviewed. This included direct information from microbiological observations on human and animal material as well as subsidiary information derived from pertinent dietary studies and histological examination of cemental lesions. Early investigations on root surface caries in experimental animals have provided valuable insight into some of the dietobacterial interactions involved. However, these ideas have not been completely validated at the human level. It was concluded that interactions between oral bacteria and other factors involved in the development of root surface dental caries may be broader in scope and more difficult to interpret than the bacterial activities which result in coronal caries.     

Mineral Surface Directed Membrane Assembly

The transition from non-living to living matter may have resulted from the self-organizing properties of organic molecules and their interactions with a chemically rich inorganic environment. We have shown that a solution containing RNA, fatty acids and clay produces structures that contain a potentially catalytic surface (clay) and a potential informational biopolymer (RNA) encapsulated within a membrane. This highlights the ability of mineral surfaces to bring together and organize key components of primordial life. We have extended our analysis of mineral-mediated vesicle catalysis to include other natural minerals and synthetic surfaces of varying shape, size, and charge density. Our results show that while RNA polymerization on minerals may be restricted to the surface environment provided by montmorillonite, vesicle formation is enhanced in the presence of disparate types of surfaces. A model is presented in which new sheets of amphiphiles form just proximal to a surface. Similar interactions between amphiphiles and minerals on early Earth may have resulted in the encapsulation of a diverse array of mineral particulates with catalytic properties.     

Imaging of Surfaces by Concurrent Surface Plasmon Resonance and Surface Plasmon Resonance-Enhanced Fluorescence

Surface plasmon resonance imaging and surface plasmon induced fluorescent are sensitive tools for surface analysis. However, existing instruments in this area have provided limited capability for concurrent detection, and may be large and expensive. We demonstrate a highly cost-effective system capable of concurrent surface plasmon resonance microscopy (SPRM) and surface plasmon resonance-enhanced fluorescence (SPRF) imaging, allowing for simultaneous monitoring of reflectivity and fluorescence from discrete spatial regions. The instrument allows for high performance imaging and quantitative measurements with surface plasmon resonance, and surface plasmon induced fluorescence, with inexpensive off-the-shelf components.     

Surface appendages of bacterial spores

Bacilli and Clostridia generate dormant, highly resistant cells, called spores, in response to stress. Spores of many species are decorated by morphologically diverse structures of unknown function called appendages that have yet to be studied at the molecular level. In this issue, Walker et al. employ reverse genetics to identify genes encoding protein components of the ornate ribbon-like appendages of the spores of Clostridium taeniosporum. Their results reveal striking commonalities between these genes and those encoding outer structures in phylogenetically and taxonomically distinct spore-forming species. The insights gained from this work demonstrate the value of analysis of non-model spore formers.     

The Surface of the African Trypanosomes1,2

The African trypanosomes bear on the outside of their cell membrane a single 10–15 nm thick coat of a glycoprotein. This glycoprotein may differ in structure in the predominant populations of parasitemic waves found in relapsing infections. Variant Specific Glycoprotein (VSG) range in MW between 53,000–63,000 d and may have variable amounts of carbohydrate attached at one, two, or several loci. Such differences in carbohydrate content may account in part for their range in molecular size. Approximately 30 C-terminal residues demonstrate isotypy; i.e. these regions fall into classes having similar amino acid sequence. Modest homology has been demonstrated in two VSGs of T. congolense arising in relapsing infections although comparison of many VSG show little or no obvious homology. More recently, lipid-associated forms of VSG have been described and it is believed that these forms may be transmembrane proteins. Different VSGs appear to have different amounts of the primary sequence which have alpha-helix-forming potential. In some VSG, in excess of 80% of the structure is helical as judged by both Chou-Fasman calculations and by circular dichroism. This raises the possibility that different VSG may have different folding patterns. The arrangement of VSG on the trypanosome surface probably places the basic amino acid-rich carbohydrate-bearing C-terminus of the polypeptide chain close to the membrane. There is some protein-protein association between VSGs for which (in T. evansi) the C-terminal tail is not required. The importance of VSG structure lies not only in the fact that the molecule mediates the phenomenon of antigenic variation but also in the recent observation that VSG may act on the cellular immune system to suppress the humoral immune responses of the host.     

Surface immobilization of plant cells

A novel technique has been developed to immobilize plant cells. The cells are deposited on a surface of manmade fibrous material that provides for strong binding of the plant tissue biomass growing in the submerged culture. The immobilized plant cells remain fully viable. Relatively uniform biomass loadings of up to 20 mg d.w. plant cells/cm(2) support material have been attained. All plant cells from the inoculum suspension became attached within the first 24-48 h depending on the support matrix configuration and hydraulic culture conditions. The advantages and scale-up potential of this technique are discussed and compared to other culturing modes.     

Surface deformation tracking and modelling of soft materials

Biomechanics and Modeling in Mechanobiology - Many computer vision algorithms have been presented to track surface deformations, but few have provided a direct comparison of measurements with other...     

Surface microwave discharges in air

A microwave discharge excited on the outer surface of a dielectric antenna has been investigated. The transverse and longitudinal dimensions and propagation velocities of the discharge have been measured as functions of the air pressure and the power and duration of the exciting microwave pulse. The spatial distributions and time evolution of the gas temperature, electron density, and radiation intensity of the discharge have been determined. It is shown that the degree of ionization of the discharge plasma can exceed 10%. The spatial distribution of the electron density is found to depend strongly on the air pressure.     

Surface Rodlets of Tilletia indica Teliospores

Tilletia indica teliospores were studied by use of thin sections and freeze-etch replicas. Surfaces of these spores have rodlet patterns which differ from those previously reported for spores of other fungi. The rodlets on T. indica teliospores average 240 nm in length and are not grouped into fascicles.     

Cell Response to Surface Stimulation

The injection of anti-D into Rh-negative subjects who have Rh-positive red cells in the circulation results in the inhibition of immunization against the D-antigen¹. On the other hand, subjects who have had a primary anti-D response to Rh-positive red cells frequently give a good secondary response to small doses of red cells despite the presence of anti-D in their plasma. The difference in action between the passively-administered and the actively-produced anti-D might lie in the fact that the injected IgG anti-D is derived from a pool of donors and therefore contains a number of IgG antigens which are foreign to the recipient, compared with the autologous nature of the anti-D present after a primary response.     

Surface charges on membranes

Summary The equations of membrane potential developed by Kobatake and coworkers have been applied to the literature data on the resting membrane potential of the crayfish andMyxicola axons to derive values for the surface charge density present on the axon membranes. Some shortcomings of the method are briefly discussed. The value for the surface charge density derived for the squid axon membrane agreed with a similar value derived from measurements of shifts in Na and/or potassium conductance-voltage relations following changes in the concentration of calcium in the solutions bathing the axons.     

Surface properties of Vibrio vulnificus

AIMS: Vibrio vulnificus adheres to a diverse range of surfaces, ranging from the chitinous exoskeleton of mollusks to human tissue. To determine whether environmental and human clinical isolates exhibit different adhesion traits, we studied the ability of 10 environmental isolates and 10 clinical isolates to adhere to human epithelial cells and hydrocarbons with log P values ranging from 3.1 to 8.2. METHODS AND RESULTS: All isolates adhered to varying levels to epithelial cells, and were inhibited to various extents from adherence by mannose and fructose. There was a lack of correlation between adherence to either hydrocarbons or cells and colony opacity. Adherence to hydrocarbons was optimal for solvents with a log P < 8.2. CONCLUSIONS: Vibrio vulnificus clinical and environmental isolates exhibit differential adherence to epithelial cells and hydrocarbons. SIGNIFICANCE AND IMPACT OF THE STUDY: The differential adherence of organisms to hydrocarbons based on log P may have utility in drug design and enhancement of food safety.     

Surface Plasmon Resonances of Clustered Nanoparticles

Linear clusters made by tightly connecting two or more metallic nanoparticles have new types of surface plasmon resonances as compared with isolated nanoparticles. These new resonances are sensitive to the size of the junction and to the number of interconnected particles and are described by eigenmodes of a boundary integral equation. This formulation allows effective separation of geometric and shape contribution from electric properties of the constituents. Results for particles covered by a thin shell are also provided highlighting ultrasensitive sensing applications. The present analysis sheds a new light on the interpretation of recent experiments.     

Staphylococcal Surface Display of Metal-Binding Polyhistidyl Peptides

Recombinant Staphylococcus xylosus and Staphylococcus carnosus strains were generated with surface-exposed chimeric proteins containing polyhistidyl peptides designed for binding to divalent metal ions. Surface accessibility of the chimeric surface proteins was demonstrated and the chimeric surface proteins were found to be functional in terms of metal binding, since the recombinant staphylococcal cells were shown to have gained Ni²⁺- and Cd²⁺-binding capacity, suggesting that such bacteria could find use in bioremediation of heavy metals. This is, to our knowledge, the first time that recombinant, surface-exposed metal-binding peptides have been expressed on gram-positive bacteria. Potential environmental or biosensor applications for such recombinant staphylococci as biosorbents are discussed.     

Surface modification of bioresorbable polymer scaffolds by laser treatment

The effect of laser irradiation on the properties of the surface of films prepared from a bioresorbable polymer poly(hydroxybuturate) has been studied. To determine the spectral region of the polymer optimal for the effective action of radiation on electron molecular bonds, theoretical investigations have been performed, which have shown that, for modifying the surface of PHB scaffolds, it is expedient to use a vacuum laser at a wavelength of 160 nm. Using laser irradiation at a power from 3 to 30 W, a series of films with modified surface, from roughnesses to perforations, have been obtained. The microstructure and properties of the film surface depending on the mode of irradiation have been examined, and conditions have been found under which the contact marginal angles of film wetting with water can be decreased to 50° (compared with 76–80° in starting products). Thus, conditions of laser treatment of PHB scaffolds have been theoretically substantiated and experimentally realized that provide a beneficial effect on the properties of the surface without destroying the structure of the material.     

All-Optical Surface Plasmonic Universal Logic Gate Devices

We have introduced optically controlled two-stage cascaded surface plasmonic two-mode interference waveguide structure (having silicon core and silver upper and lower cladding) as universal gates. GaAsInP cladding is used in left and right side of core for optical pulse controlled cladding refractive index modulation which controls propagation of excited modes. The universal logic gate operations have been shown with this structure. These universal gates have potential in development of large-scale integrated optical processor due to its compactness and high fabrication tolerance.