A universal homogeneous assay for high-throughput determination of binding kinetics

There is an increasing demand for assay technologies that enable accurate, cost-effective, and high-throughput measurements of drug–target association and dissociation rates. Here we introduce a universal homogeneous kinetic probe competition assay (kPCA) that meets these requirements. The time-resolved fluorescence energy transfer (TR–FRET) procedure combines the versatility of radioligand binding assays with the advantages of homogeneous nonradioactive techniques while approaching the time resolution of surface plasmon resonance (SPR) and related biosensors. We show application of kPCA for three important target classes: enzymes, protein–protein interactions, and G protein-coupled receptors (GPCRs). This method is capable of supporting early stages of drug discovery with large amounts of kinetic information.     

A surface display yeast two-hybrid screening system for high-throughput protein interactome mapping

Despite the wide acceptance of yeast two-hybrid (Y2H) system for protein-protein interaction analysis and discovery, conventional Y2H assays are not well suited for high-throughput screening of the protein interaction network (“interactome”) on a genomic scale due to several limitations, including labor-intensive agar plating and colony selection methods associated with the use of nutrient selection markers, complicated reporter analysis methods associated with the use of LacZ enzyme reporters, and incompatibility of the liquid handling robots. We recently reported a robust liquid culture Y2H system based on quantitative analysis of yeast-enhanced green fluorescent protein (yEGFP) reporters that greatly increased the analysis throughput and compatibility with liquid handling robots. To further advance its utility in high-throughput complementary DNA (cDNA) library screening, we report the development of a novel surface display Y2H (sdY2H) library screening system with uniquely integrated surface display hemagglutination (sdHA) antigen and yEGFP reporters. By introduction of a surface reporter sdHA into the yEGFP-based Y2H system, positive Y2H targets are quickly isolated from library cells by a simple magnetic separation without a large plating effort. Moreover, the simultaneous scoring of multiple reporters, including sdHA, yEGFP, and conventional nutrient markers, greatly increased the specificity of the Y2H assay. The feasibility of the sdY2H assay on large cDNA library screening was demonstrated by the successful recovery of positive P53/T interaction pairs at a target-to-background ratio of 1:1,000,000. Together with the massive parallel DNA sequencing technology, it may provide a powerful proteomic tool for high-throughput interactome mapping on a genomic scale.     

PRISM: a data management system for high-throughput proteomics

Advanced proteomic research efforts involving areas such as systems biology or biomarker discovery are enabled by the use of high level informatics tools that allow the effective analysis of large quantities of differing types of data originating from various studies. Performing such analyses on a large scale is not feasible without a computational platform that performs data processing and management tasks. Such a platform must be able to provide high-throughput operation while having sufficient flexibility to accommodate evolving data analysis tools and methodologies. The Proteomics Research Information Storage and Management system (PRISM) provides a platform that serves the needs of the accurate mass and time tag approach developed at Pacific Northwest National Laboratory. PRISM incorporates a diverse set of analysis tools and allows a wide range of operations to be incorporated by using a state machine that is accessible to independent, distributed computational nodes. The system has scaled well as data volume has increased over several years, while allowing adaptability for incorporating new and improved data analysis tools for more effective proteomics research.     

Surface plasmon resonance imaging-based protein arrays for high-throughput screening of protein-protein interaction inhibitors

The E7 protein produced by high-risk human papillomavirus (HPV) induces a degradation of the retinoblastoma tumor suppressor RB through direct interaction, which suggests that an inhibitor for the interaction can be a potential anticancer drug. A surface plasmon resonance (SPR) imaging-based protein array chip was developed for the high-throughput screening of inhibitor molecules targeting RB-E7 interaction. The glutathione S-transferase-fused E7 protein (GST-E7) was first layered onto a glutathionylated gold chip surface that had been designed to specifically bind to GST-fused proteins. Subsequently, a microarrayer was used to spot the hexa-histidine-tagged RB proteins (His(6)-RB) onto the GST-E7-layered gold chip surface, and the resulting SPR image was analyzed. Upon increased His(6)-RB concentration in the spotting solution, the SPR signal intensity increased proportionally, indicating that His(6)-RB bound to GST-E7 in a concentration-dependent manner. The His(6)-RB/GST-E7 interaction was challenged by spotting the His(6)-RB solution in the presence of a RB binding peptide (PepC) derived from a motif on E7. The SPR imaging data showed that PepC inhibited the His(6)-RB/GST-E7 interaction in a concentration-dependent manner. Our results show that the SPR imaging-based protein array chip can be applied to screen small molecule inhibitors that target protein-protein interaction.     

Microarray TRAP--a high-throughput assay to quantitate telomerase activity

Telomeric repeat amplification protocol (TRAP)--a sensitive, PCR-based assay to detect telomerase activity was quintessential to the evaluation of telomerase role in telomere maintenance, cell proliferation, tumour development, and cell immortalization. The assay, however, suffers from many limitations. The most significant are: lack of telomerase activity quantification, changes of the enzyme activity product size and/or ratio, and complex post-amplification procedures which limit the assay throughput. Here we report the development of the microarray TRAP (MTRAP) assay which combines advantages of microarray technology with a modified TRAP assay. The MTRAP was designed and optimized on rice cell suspension telomerase extract to enable telomerase specific, reliable, and linear quantification in high throughput mode, with sensitivity comparable to those of radioisotope-based TRAP assays. The MTRAP has a built-in system guaranteeing the amplification of telomerase activity products unchanged in length and/or ratio and built-in control for false negatives. Thus, our MTRAP assay provides new reliable tool for experiments requiring massive quantitation of telomerase activity.     

Optimized beadmilling of tissues for high-throughput RNA production and microarray-based analyses

The preparation of RNA samples has become the rate-limiting step when performing genome-scale analyses by DNA microarrays. Methods to improve throughput of RNA isolation from tissues are needed. The effects of bead size and composition for disrupting mouse tissues have been evaluated in small centrifuge tubes and optimized for RNA production. The resulting process is inexpensive, resistant to cross-contamination, and amenable to robotic processing. After optimization, very-high-quality RNA can be produced. Comparisons between RNAs isolated by beadmilling (followed by solid-phase purification) and those by conventional isolation processes show that RNA produced by beadmilling is suitable for microarray analyses. Parallel implementation of beadmilling will enable a high-throughput tissue-to-RNA processing system for large-scale microarray analyses.     

Automated high-throughput process for site-directed mutagenesis, production, purification, and kinetic characterization of enzymes

Site-directed mutagenesis followed by functional characterization is a widely used approach to obtain information on the structure-function relationship of proteins. Due to time and cost considerations, the number of amino acids studied is frequently reduced. To address the need for convenient parallel production of numerous point mutants of a protein, we developed an automated method to perform classical site-directed mutagenesis, protein purification, and characterization in a high-throughput manner. The process consists of a succession of six fully automated protocols that can be adapted to any automated liquid handling systems. Our procedure allows construction, validation, and characterization of hundreds of site-directed mutants of a given protein in just 4 days. The method is especially adapted to projects aiming at the study of unique or multiple mutants without the need to construct and screen large libraries of random mutants. The usefulness of the technique is illustrated by the construction and characterization of tens of single mutants of the penicillin-binding protein 2x (PBP2x) from Streptococcus pneumoniae. Moreover, seven mutations of PBP2x were obtained simultaneously in a single experiment with efficiency close to 90%.     

Protein and peptide identification algorithms using MS for use in high-throughput, automated pipelines

Current proteomics experiments can generate vast quantities of data very quickly, but this has not been matched by data analysis capabilities. Although there have been a number of recent reviews covering various aspects of peptide and protein identification methods using MS, comparisons of which methods are either the most appropriate for, or the most effective at, their proposed tasks are not readily available. As the need for high-throughput, automated peptide and protein identification systems increases, the creators of such pipelines need to be able to choose algorithms that are going to perform well both in terms of accuracy and computational efficiency. This article therefore provides a review of the currently available core algorithms for PMF, database searching using MS/MS, sequence tag searches and de novo sequencing. We also assess the relative performances of a number of these algorithms. As there is limited reporting of such information in the literature, we conclude that there is a need for the adoption of a system of standardised reporting on the performance of new peptide and protein identification algorithms, based upon freely available datasets. We go on to present our initial suggestions for the format and content of these datasets.     

A thin quartz cell suitable for vacuum ultraviolet absorption and circular dichroism measurements

The design of a thin quartz cell suitable for absorption and circular dichroism measurements in the vacuum ultraviolet is described. Important features of the cell are (1) that it can be disassembled for cleaning and reproducibly reassembled with path lengths up to 0.3 mm, and (2) that strain in the windows from the compressed sample can be relieved by a sample overflow port. The latter feature allows the cell to be used for circular dichroism as well as absorption measurements.     

A high-throughput screening fluorescence polarization assay for fatty acid adenylating enzymes in Mycobacterium tuberculosis

Mycobacterium tuberculosis, the etiological agent of tuberculosis (TB), encodes for an astonishing 34 fatty acid adenylating enzymes (FadDs), which play key roles in lipid metabolism. FadDs involved in lipid biosynthesis are functionally nonredundant and serve to link fatty acid and polyketide synthesis to produce some of the most architecturally complex natural lipids including the essential mycolic acids as well as the virulence-conferring phthiocerol dimycocerosates, phenolic glycolipids, and mycobactins. Here we describe the systematic development and optimization of a fluorescence polarization assay to identify small molecule inhibitors as potential antitubercular agents. We fluorescently labeled a bisubstrate inhibitor to generate a fluorescent probe/tracer, which bound with a K_D of 245 nM to FadD28. Next, we evaluated assay performance by competitive binding experiments with a series of known ligands and assessed the impact of control parameters including incubation time, stability of the signal, temperature, and DMSO concentration. As a final level of validation the LOPAC1280 library was screened in a 384-well plate format and the assay performed with a Z-factor of 0.75, demonstrating its readiness for high-throughput screening.     

Screening for lysine-specific demethylase-1 inhibitors using a label-free high-throughput mass spectrometry assay

Posttranslational modifications on the N terminus of histone H3 act in a combinatorial fashion to control epigenetic responses to extracellular stimuli. Lysine-specific demethylase-1 (LSD1) represents an emerging epigenetic target class for the discovery of novel antitumor therapies. In this study, a high-throughput mass spectrometry (HTMS) assay was developed to measure LSD1-catalyzed demethylation of lysine-4 on several H3 substrates. The assay leverages RapidFire chromatography in line with a triple stage quadrupole detection method to measure multiple LSD1 substrate and product reactions from an assay well. This approach minimizes artifacts from fluorescence interference and eliminates the need for antibody specificity to methylated lysines. The assay was robust in a high-throughput screen of a focused library consisting of more than 56,000 unique chemical scaffolds with a median Z′ of 0.76. Validated hits from the primary screen were followed up by successive rounds of virtual and HTMS screening to mine for related structures in a parent library consisting of millions of compounds. The screen resulted in the rapid discovery of multiple chemical classes amenable to medicinal chemistry optimization. This assay was further developed into a generic platform capable of rapidly screening epigenetic targets that use the N-terminal tail of histone H3 as a substrate.     

New vectors for co-expression of proteins: structure of Bacillus subtilis ScoAB obtained by high-throughput protocols

The Bacillus subtilis genes scoA and scoB encode subunits of the heteromeric enzyme ScoAB, a putative succinyl-CoA:acetoacetate coenzyme A transferase. High-throughput, ligation-independent cloning (LIC) vectors used extensively for production and purification of single proteins were modified to allow simultaneous expression of interacting proteins and selective purification of functional complexes. Transfer of the LIC region of vector pMCSG7 (L. Stols, M. Gu, L. Dieckman, R. Raffen, F.R. Collart, M.I. Donnelly. A new vector for high-throughput, ligation-independent cloning encoding a tobacco etch virus protease cleavage site. Protein Expr. Purif. (2002) 25, 8–15) into commercial vectors with alternative, compatible origins of replication allowed introduction of standard LIC PCR products into the vectors by uniform protocols. Replacement of the His-tag encoding region of pMCSG7 with a sequence encoding the S-tag enabled selective purification of interacting proteins based on the His-tag associated with one member of the complex. When expressed separately and mixed, the ScoAB subunits failed to interact productively; no transferase activity was detected, and S-tagged ScoB failed to co-purify with His-tagged ScoA. Co-expression, in contrast, generated active transferase that catalyzed the predicted reaction. The ScoAB complex was purified by standard high-throughput metal-ion affinity chromatography procedures, crystallized robotically, and its structure was determined by molecular replacement.     

Microplate assay for endo-polygalacturonase activity determination based on ruthenium red method

Endo-polygalacturonase (endo-PGase) activity determinations generally rely on viscosity changes or reducing sugar ends produced by this activity over polygalacturonic acid. Torres and coworkers [Enzyme Microb. Technol. 48 (2011) 123–128] showed that ruthenium red (RR) is useful for endo-PGase determination. In this article, we present a high-throughput liquid-based endo-PGase assay based on the RR method and compare it with the viscosity determination method. The reduced assay uses a small volume of enzyme solution, 40 μg of polygalacturonic acid, and 45 μg of RR for each sample determination. Furthermore, we obtained an interconversion factor for RR and viscosity activities.     

A novel assay for monoacylglycerol hydrolysis suitable for high-throughput screening

A simple assay for monoacylglycerol hydrolysis suitable for high-throughput screening is described. The assay uses [(3)H]2-oleoylglycerol as substrate, with the tritium label in the glycerol part of the molecule and the use of phenyl sepharose gel to separate the hydrolyzed product ([(3)H]glycerol) from substrate. Using cytosolic fractions derived from rat cerebella as a source of hydrolytic activity, the assay gives the appropriate pH profile and sensitivity to inhibition with compounds known to inhibit hydrolysis of this substrate. The assay could also be adapted to a 96-well plate format, using C6 cells as the source of hydrolytic activity. Thus the assay is simple and appropriate for high-throughput screening of inhibitors of monoacylglycerol hydrolysis.     

A protocol for high-throughput phenotyping, suitable for quantitative trait analysis in mice

Whole-genome genetic association studies in outbred mouse populations represent a novel approach to identifying the molecular basis of naturally occurring genetic variants, the major source of quantitative variation between inbred strains of mice. Measuring multiple phenotypes in parallel on each mouse would make the approach cost effective, but protocols for phenotyping on a large enough scale have not been developed. In this article we describe the development and deployment of a protocol to collect measures on three models of human disease (anxiety, type II diabetes, and asthma) as well as measures of mouse blood biochemistry, immunology, and hematology. We report that the protocol delivers highly significant differences among the eight inbred strains (A/J, AKR/J, BALBc/J, CBA/J, C3H/HeJ, C57BL/6 J, DBA/2 J, and LP/J), the progenitors of a genetically heterogeneous stock (HS) of mice. We report the successful collection of multiple phenotypes from 2000 outbred HS animals. The phenotypes measured in the protocol form the basis of a large-scale investigation into the genetic basis of complex traits in mice designed to examine interactions between genes and between genes and environment, as well as the main effects of genetic variants on phenotypes.     

Structural and functional changes in complement protein C4 under UV irradiation

The influence of ultraviolet (UV) light on the structural and functional states of the complement factor C4 was investigated using hemolytic and acid-base titration, PAG electrophoresis, and IR and UV spectrophotometry. UV doses of 75.5 and 755 J/m² initiated C4 activation through changes in the globule structure (increased number of aromatic amino acids and ionogenic groups at the surface). The maximal dose of 2265 J/m² has a destructive effect and decreases its C4 activity in the cascade of hemolytic reactions of the complement system.     

Simplified high-throughput screening of AOX1-expressed laccase enzyme in Pichia pastoris

The heterologous protein expression in Pichia pastoris under the control of alcohol oxidase (AOX1)promoter comprises two steps, the growth and induction phases, which are time-consuming and technically demanding. Here, we describe an alternate method where expression is carried out directly in the methanol-containing medium. Using this method, we were successful in screening high-activity laccase clones from a library of laccase mutants generated by random mutagenesis. This simplified method not only saves time but also is highly efficient and can be used for screening a large number of clones.