Peptide microarrays for serum antibody diagnostics.

Peptide microarrays are useful instruments for miniaturized high-throughput, high-content immunoassays. The substitution of linear epitopes of the protein antigen with short, synthetic peptides is virtually a straightforward approach to capture antigen-specific antibodies from serum samples; however, both the biologically active surface display of peptides and the establishment of a solidly performing peptide microarray immunoassay are often troublesome in detail. The following protocols aim to provide facilitated access to the production of a robust peptide microarray platform and an optimized analytical processing of peptide microarrays in serological diagnosis. The functional surface display is accomplished by site-specific immobilization of peptide probes in a two-step procedure first by coupling of biotinylated peptides to hydrazide-modified streptavidin and then utilizing a subsequent chemoselective reaction between the hydrazide linkers of the streptavidin and an aldehyde-coated substrate for microstructured surface immobilization of the probe complexes. The serological assay is based on the specific capture of primary antibodies in a sandwich complex between the surface-immobilized peptides and a fluorescently labelled secondary antibody. A proposal for the diagnostic evaluation of fluorescence data obtained with the peptide microarray is also made.

Development of peptide microarrays for epitope mapping of antibodies against the human TSH receptor.

Accurate characterization of the antigen binding region of antibodies is of great value in many fields of research, assay development and clinical diagnostics. Up to now, there is an unmet clinical need to use antibodies as diagnostic markers for the prediction of both prognosis and therapeutic response. To this end, comprehensive but differentiated immunoassays need to be generated. We have developed a peptide microarray for the diagnosis and epitope mapping of anti-thyrotropin receptor antibodies. The primary sequence of the human thyrotropin receptor (hTSHR) was represented by a library of 251 synthetic peptides. The peptides were site-specifically immobilized in a two-step procedure first by coupling of biotinylated peptides to hydrazide-modified streptavidin and then utilizing a subsequent chemoselective reaction between the hydrazide linkers of the streptavidin and an aldehyde coated glass surface. The technology was used to map the epitopes of seven commercially available murine monoclonal antibodies specific for the human TSH receptor (mTSHRAb). A previously unknown epitope recognized by mTSHRAb 4C1 was identified at amino acids (AA) 379 through 384 and the epitope recognized by mTSHRAb A9 was also localized (AA 214-222). Previously identified epitopes recognized by mTSHRAbs 2C11 (AA 349-360), 28 (AA 34-39), 49 (AA 289-297), A7 (AA 406-411) and A10 (AA 34-39) were confirmed. The peptide microarray exhibited excellent performance in single and multiplex antibody analysis and high specificity. This technology may have potential as a multi-determinate in vitro diagnostic assay for the differential analysis of a heterogeneity of antibodies involved in the pathogenesis of autoimmune diseases.

Peptide microarrays with site-specifically immobilized synthetic peptides for antibody diagnostics.

Peptide microarrays bear the potential to discover molecular recognition events on protein level, particularly in the field of molecular immunology, in a manner and with an efficiency comparable to the performance of DNA microarrays. We developed a novel peptide microarray platform for the detection of antibodies in liquid samples. The system comprises site-specific solution phase coupling of biotinylated peptides to NeutrAvidin, localized microdispensing of peptide-NeutrAvidin conjugates onto activated glass slides and a fluorescence immuno sandwich assay format for antibody capture and detection. Our work includes synthetic peptides deduced from amino acid sequences of immunodominant linear epitopes, such as the T7 phage capsid protein, Herpes simplex virus glycoprotein D, c-myc protein and three domains of the Human coronavirus 229E polymerase polyprotein. We demonstrate that our method produces peptide arrays with excellent spot morphology which are capable of specific and sensitive detection of monoclonal antibodies from fluid samples.

Identification of pathogenic microbial cells and spores by electrochemical detection on a biochip.

BACKGROUND: Bacillus cereus constitutes a significant cause of acute food poisoning in humans. Despite the recent development of different detection methods, new effective control measures and better diagnostic tools are required for quick and reliable detection of pathogenic micro-organisms. Thus, the objective of this study was to determine a simple method for rapid identification of enterotoxic Bacillus strains. Here, a special attention is given to an electrochemical biosensor since it meets the requirements of minimal size, lower costs and decreased power consumption. RESULTS: A bead-based sandwich hybridization system was employed in conjugation with electric chips for detection of vegetative cells and spores of Bacillus strains based on their toxin-encoding genes. The system consists of a silicon chip based potentiometric cell, and utilizes paramagnetic beads as solid carriers of the DNA probes. The specific signals from 20 amol of bacterial cell or spore DNA were achieved in less than 4 h. The method was also successful when applied directly to unpurified spore and cell extract samples. The assay for the haemolytic enterotoxin genes resulted in reproducible signals from B. cereus and B. thuringiensis while haemolysin-negative B. subtilis strain did not yield any signal. CONCLUSIONS: The sensitivity, convenience and specificity of the system have shown its potential. In this respect an electrochemical detection on a chip enabling a fast characterization and monitoring of pathogens in food is of interest. This system can offer a contribution in the rapid identification of bacteria based on the presence of specific genes without preceding nucleic acid amplification.

Kinetic investigation of bioresponsive nanoparticle assembly as a function of ligand design.

Homogeneous and heterogeneous nanoparticle (NP) assembly induced by ligand-specific immunorecognition is commonly used for biosensing applications. We investigated how the structural design of the peptide ligands used to functionalise gold NPs affected the kinetics of NP assembly and hence biodetection. We observed that aggregation rates varied up to 20-fold for the surface binding and 120-fold for the solution-phase assembly of NPs as a function of peptide design. Our results show how the fundamental difference in NP assembly on surfaces and in solution requires different optimised ligand designs. This increased understanding of the specifics of ligand-triggered NP aggregation should help in the design of faster and more efficient bioassays in the future.

SPOT synthesis as a tool to study protein-protein interactions.

Peptide arrays are a widely used tool in proteomic research for investigations of drug development and molecular interactions including protein-protein or protein-peptide interactions. Most peptide synthesis techniques are able to simultaneously synthesize only up to a few hundred single peptides. Using the SPOT™ technique, it is possible to synthesize and screen in parallel up to 8,000 peptides or peptide mixtures. In addition, such peptides can be released from the membrane and transferred onto peptide microarrays. Here we present protocols for the peptides synthesis on cellulose including the preparation of different cellulose membranes and easy-to-use detection methods on these peptide macroarrays. In addition, a protocol to produce and screen peptide microarray using the SPOT technology is provided.

Single-step kinase inhibitor screening using a peptide-modified gold nanoparticle platform.

Two complementary formats for kinase inhibitor screening are presented in which peptide-modified gold nanoparticles are enzymatically phosphorylated and rapidly aggregate on a surface or in solution by action of phosphospecific antibodies. The simple and rapid colourimetric response of the assays makes them an attractive approach for drug-screening applications.

Functional peptide microarrays for specific and sensitive antibody diagnostics.

Peptide microarrays displaying biologically active small synthetic peptides in a high-density format provide an attractive technology to probe complex samples for the presence and/or function of protein analytes. We present a new approach for manufacturing functional peptide microarrays for molecular immune diagnostics. Our method relies on the efficiency of site-specific solution-phase coupling of biotinylated synthetic peptides to NeutrAvidin (NA) and localized microdispensing of peptide-NA-complexes onto activated glass surfaces. Antibodies are captured in a sandwich manner between surface immobilized peptide probes and fluorescence-labeled secondary antibodies. Our work includes a total of 54 peptides derived from immunodominant linear epitopes of the T7 phage capsid protein, Herpes simplex virus glycoprotein D, c-myc protein, and three domains of the Human coronavirus polymerase polyprotein and their cognate mAbs. By using spacer molecules of different type and length for NA-mediated peptide presentation, we show that the incorporation of a minimum spacer length is imperative for antibody binding, whereas the peptide immobilization direction has only secondary importance for antibody affinity and binding. We further demonstrate that the peptide array is capable of detecting low-picomolar concentrations of mAbs in buffered solutions and diluted human serum with high specificity.