A procedure for protein elution from reverse-stained polyarcylamide gels applicable at the low picomole level: An alternative route to the preparation of low abundance proteins for microanalysis

Ningnanmycin inhibits tobacco mosaic virus virulence by binding directly to its coat protein discs

Tobacco mosaic virus (TMV) causes severe plant diseases worldwide; however, effective antiviral agents for controlling TMV infections are not available. This lack of effective antiviral agents is mainly due to the poor understanding of potential targets associated with TMV infections. During infection, the coat protein (CP), which is delivered by viral particles into susceptible host cells, provides protection for viral RNA. Here, we found that Ningnanmycin (NNM), a commercially used plant antibacterial agent, inhibits the assembly of the CP by directly binding several residues. These interactions cause the disassembly of the CP from discs into monomers, leading to an almost complete loss of pathogenicity. Substitutions in the involved binding residues resulted in mutants that were significantly less sensitive to NNM. Thus, targeting the binding of viral CPs through small molecular agents offers an effective strategy to study the mechanism of NNM.

Analytical purification of a 60-kDa target protein of artemisinin detected in Trypanosoma brucei brucei

Here we describe the isolation and purity determination of Trypanosoma brucei (T. b.) brucei candidate target proteins of artemisinin. The candidate target proteins were detected and purified from their biological source (T. b. brucei lysate) using the diazirine-free biotinylated probe 5 for an affinity binding to a streptavidin-tagged resin and, subsequently, the labeled target proteins were purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). We herein showed the electrophoresis gel and the immunoblotting film containing the 60-kDa trypanosomal candidate target protein of artemisinin as a single band, which was visualized on-gel by the reverse-staining method and on a Western blotting film by enhanced chemiluminescence. The data provided in this article are related to the original research article "Biotinylated probes of artemisinin with labeling affinity toward Trypanosoma brucei brucei target proteins", by Konziase (Anal. Biochem., vol. 482, 2015, pp. 25-31. http://dx.doi.org/10.1016/j.ab.2015.04.020).

Crystal structure of a four-layer aggregate of engineered TMV CP implies the importance of terminal residues for oligomer assembly

Background

Crystal structures of the tobacco mosaic virus (TMV) coat protein (CP) in its helical and disk conformations have previously been determined at the atomic level. For the helical structure, interactions of proteins and nucleic acids in the main chains were clearly observed; however, the conformation of residues at the C-terminus was flexible and disordered. For the four-layer aggregate disk structure, interactions of the main chain residues could only be observed through water–mediated hydrogen bonding with protein residues. In this study, the effects of the C-terminal peptides on the interactions of TMV CP were investigated by crystal structure determination.

Methodology/Principal Findings

The crystal structure of a genetically engineered TMV CP was resolved at 3.06 Å. For the genetically engineered TMV CP, a six-histidine (His) tag was introduced at the N-terminus, and the C-terminal residues 155 to 158 were truncated (N-His-TMV CP¹⁹). Overall, N-His-TMV CP¹⁹ protein self-assembled into the four-layer aggregate form. The conformations of residues Gln36, Thr59, Asp115 and Arg134 were carefully analyzed in the high radius and low radius regions of N-His-TMV CP¹⁹, which were found to be significantly different from those observed previously for the helical and four-layer aggregate forms. In addition, the aggregation of the N-His-TMV CP¹⁹ layers was found to primarily be mediated through direct hydrogen-bonding. Notably, this engineered protein also can package RNA effectively and assemble into an infectious virus particle.

Conclusion

The terminal sequence of amino acids influences the conformation and interactions of the four-layer aggregate. Direct protein–protein interactions are observed in the major overlap region when residues Gly155 to Thr158 at the C-terminus are truncated. This engineered TMV CP is reassembled by direct protein–protein interaction and maintains the normal function of the four-layer aggregate of TMV CP in the presence of RNA.

Quantitative proteomics: assessing the spectrum of in-gel protein detection methods

Proteomics research relies heavily on visualization methods for detection of proteins separated by polyacrylamide gel electrophoresis. Commonly used staining approaches involve colorimetric dyes such as Coomassie Brilliant Blue, fluorescent dyes including Sypro Ruby, newly developed reactive fluorophores, as well as a plethora of others. The most desired characteristic in selecting one stain over another is sensitivity, but this is far from the only important parameter. This review evaluates protein detection methods in terms of their quantitative attributes, including limit of detection (i.e., sensitivity), linear dynamic range, inter-protein variability, capacity for spot detection after 2D gel electrophoresis, and compatibility with subsequent mass spectrometric analyses. Unfortunately, many of these quantitative criteria are not routinely or consistently addressed by most of the studies published to date. We would urge more rigorous routine characterization of stains and detection methodologies as a critical approach to systematically improving these critically important tools for quantitative proteomics. In addition, substantial improvements in detection technology, particularly over the last decade or so, emphasize the need to consider renewed characterization of existing stains; the quantitative stains we need, or at least the chemistries required for their future development, may well already exist.

Inhibition of neutrophil migration by hemopexin leads to increased mortality due to sepsis in mice

RATIONALE

The reduction of neutrophil migration to the bacterial focus is associated with poor outcome in sepsis.

OBJECTIVES

The objective of this study was to identify soluble substances in the blood of septic mice that inhibit neutrophil migration.

METHODS

A pool of serum obtained from mice 2 hours after the induction of severe sepsis by cecal ligation and puncture inhibited the neutrophil migration. The proteins with inhibitory activity on neutrophil migration were isolated by Blue-Sepharose chromatography, high-performance liquid chromatography, and electrophoresis, and identified by mass spectrometry.

MEASUREMENTS AND MAIN RESULTS

Hemopexin was identified as the serum component responsible for the inhibition of neutrophil migration. In sepsis, the pretreatment of wild-type mice with hemopexin inhibited neutrophil migration to the focus of infection and decreased the survival rate from 87.5 to 50.0%. Hemopexin-null mice subjected to severe sepsis presented normal neutrophil migration, low bacteremia, and an improvement of 40% in survival rate. Moreover, hemopexin inhibited the neutrophil chemotaxis response evoked by C5a or macrophage inflammatory protein-2 and induced a reduction of CXCR2 and L-selectin as well as the up-regulation of CD11b expression in neutrophil membranes. The inhibitory effect of hemopexin on neutrophil chemotaxis was prevented by serine protease inhibitors or ATP. In addition, serum levels of ATP were decreased 2 hours after severe sepsis.

CONCLUSIONS

These data demonstrate for the first time the inhibitory role of hemopexin in neutrophil migration during sepsis and suggest that the therapeutic inhibition of hemopexin or its protease activity could improve neutrophil migration to the focus of infection and survival in sepsis.

Purification and characterization of lipopolysaccharides

Lipopolysaccharides are the major components on the surface of most Gram-negative bacteria, and recognized by immune cells as a pathogen-associated molecule. They can cause severe diseases like sepsis and therefore known as endotoxins. Lipopolysaccharide consists of lipid A, core oligosaccharide and O-antigen repeats. Lipid A is responsible for the major bioactivity of endotoxin. Because of their specific structure and amphipathic property, purification and analysis of lipopolysaccharides are difficult. In this chapter, we summarize the available approaches for extraction, purification and analysis of lipopolysaccharides.

Acute-phase protein alpha-1-acid glycoprotein mediates neutrophil migration failure in sepsis by a nitric oxide-dependent mechanism

The reduction of circulating neutrophil migration to infection sites is associated with a poor outcome of severe sepsis. alpha-1-Acid glycoprotein (AGP) was isolated from the sera of severely septic patients by HPLC and acrylamide gel electrophoresis and identified by mass spectrometry. Both the isolated protein and commercial AGP inhibited carrageenin-induced neutrophil migration into the rat peritoneal cavity when administered i.v. at a dose of 4.0 microg per rat (95 pmol per rat). Analysis by intravital microscopy demonstrated that both proteins inhibited the rolling and adhesion of leukocytes in the mesenteric microcirculation. The inhibitory activity was blocked by 50 mg/kg aminoguanidine, s.c., and was not demonstrable in inducible nitric oxide synthase (iNOS) knockout mice. Incubation of AGP with neutrophils from healthy subjects induced the production of NO and inhibited the neutrophil chemotaxis by an iNOS/NO/cyclic guanosine 3,5-monophosphate-dependent pathway. In addition, AGP induced the l-selectin shedding by neutrophils. The administration of AGP to rats with mild cecal ligation puncture sepsis inhibited neutrophil migration and reduced 7-day survival from approximately 80% to 20%. These data demonstrate that AGP, an acute-phase protein, inhibits neutrophil migration by an NO-dependent process and suggest that AGP also participates in human sepsis.

Negative detection of biomolecules separated in polyacrylamide electrophoresis gels

Here we describe the protocols for negative or reverse detection of proteins, nucleic acids and lipopolysaccharides separated in polyacrylamide electrophoresis gels. These protocols are based on the selective synthesis and precipitation of a white imidazole-zinc complex in the gel, which is absent from those zones where biomolecules are located. These methods are highly sensitive (1-10 ng of biomolecules per band), very cheap as they use inexpensive, common laboratory reagents (imidazole and a Zn II salt), rapid (less than 20 min after gel washing), robust and simple (two steps). Reverse-stained biomolecules are reversibly fixed in the gel. After brief incubation in a zinc chelating agent, biomolecules can be recovered from the gel with the same efficiency as from unstained gels. In consequence, they are procedures of choice for micropreparative applications. References covering typical applications are included.

Structure of a high-affinity "mimotope" peptide bound to HIV-1-neutralizing antibody b12 explains its inability to elicit gp120 cross-reactive antibodies

The human antibody b12 recognizes a discontinuous epitope on gp120 and is one of the rare monoclonal antibodies that neutralize a broad range of primary human immunodeficiency virus type 1 (HIV-1) isolates. We previously reported the isolation of B2.1, a dimeric peptide that binds with high specificity to b12 and competes with gp120 for b12 antibody binding. Here, we show that the affinity of B2.1 was improved 60-fold over its synthetic-peptide counterpart by fusing it to the N terminus of a soluble protein. This affinity, which is within an order of magnitude of that of gp120, probably more closely reflects the affinity of the phage-borne peptide. The crystal structure of a complex between Fab of b12 and B2.1 was determined at 1.8 A resolution. The structural data allowed the differentiation of residues that form critical contacts with b12 from those required for maintenance of the antigenic structure of the peptide, and revealed that three contiguous residues mediate B2.1's critical contacts with b12. This single region of critical contact between the B2.1 peptide and the b12 paratope is unlikely to mimic the discontinuous key binding residues involved in the full b12 epitope for gp120, as previously identified by alanine scanning substitutions on the gp120 surface. These structural observations are supported by experiments that demonstrate that B2.1 is an ineffective immunogenic mimic of the b12 epitope on gp120. Indeed, an extensive series of immunizations with B2.1 in various forms failed to produce gp120 cross-reactive sera. The functional and structural data presented here, however, suggest that the mechanism by which b12 recognizes the two antigens is very different. Here, we present the first crystal structure of peptide bound to an antibody that was originally raised against a discontinuous protein epitope. Our results highlight the challenge of producing immunogens that mimic discontinuous protein epitopes, and the necessity of combining complementary experimental approaches in analyzing the antigenic and immunogenic properties of putative molecular mimics.

Protein stains for proteomic applications: which, when, why?

This review recollects literature data on sensitivity and dynamic range for the most commonly used colorimetric and fluorescent dyes for general protein staining, and summarizes procedures for the most common PTM-specific detection methods. It also compiles some important points to be considered in imaging and evaluation. In addition to theoretical considerations, examples are provided to illustrate differential staining of specific proteins with different detection methods. This includes a large body of original data on the comparative evaluation of several pre- and post-electrophoresis stains used in parallel on a single specimen, horse serum run in 2-DE (IPG-DALT). A number of proteins/protein spots are found to be over- or under-revealed with some of the staining procedures.

Multiple gene copy number enhances insulin precursor secretion in the yeast Pichia pastoris

We have found a direct relationship between protein production in Pichia pastoris and the number of introduced synthetic genes of miniproinsulin (MPI), fused to the Saccharomyces cerevisiae pre-pro alpha factor used as secretion signal, and inserted between the alcohol oxidase 1 (AOX1) promoter and terminator sequences. Two consecutive approaches were followed to increase the number of integrated cassettes: the head-to-tail expression cassette multimerization procedure and re-transformation with a dominant selection marker. This increased expression from 19 to 250 mg l(-1) when about 11 copies have been integrated. Further, the correct position of one of the disulphide bridges of the purified molecule was verified by digestion with Glu-C endoprotease, followed by mass spectrometry of the isolated fragments.

"Reverse-staining" of biomolecules in electrophoresis gels: analytical and micropreparative applications

Negative or reverse staining using imidazole and zinc salts for protein detection in electrophoresis gels was originally introduced in 1990. The method is based on the selective precipitation of zinc imidazolate in the gel except in the zones where proteins are located. The method was later adapted to allow high-sensitivity negative detection of nucleic acids and bacterial lipopolysaccharides. It provides a practically quantitative recovery of intact biomolecules and is a method of choice for micropreparative applications of gel electrophoresis to proteomics and similar structural studies. Zinc-mediated protein fixation in the gel is fully reversible and the eluted biomolecules are neither chemically modified nor contaminated with organic dyes. Here we present a detailed compilation of practical methods for implementing these techniques with emphasis in their analytical or micropreparative applications.

Senescence marker protein-30 regulates Akt activity and contributes to cell survival in Hep G2 cells

Senescence marker protein-30 (SMP30) is highly expressed in cytosol of hepatocytes, and its amount decreases with aging. Human hepatocellular carcinoma cell line was transfected with pcDNA3/SMP30 (SMP30 transfectants), or as a control with pcDNA3 (mock transfectants). When cells were exposed to 20 ng/ml tumor necrosis factor-alpha (TNF-alpha) plus 10 ng/ml actinomycin D (Act-D) for 15 h, the viability of cells was decreased in both SMP30 and mock transfectants. However, the viability of cells was threefold higher in SMP30 transfectants than mock transfectants. Cell death was confirmed as apoptosis by TUNEL assay. The presence of trifluoperazine, a calmodulin (CaM) inhibitor, attenuated anti-apoptotic effect of SMP30 in both transfectants, but the effect was more prominent in SMP30 transfectants. Western blot analyses revealed that Akt, which acts as a survival factor in cells, was activated in SMP30, but not mock, transfectants either in the presence or absence of TNF-alpha plus Act-D. Further, trifluoperazine inhibited Akt activation in SMP30 transfectants. We therefore propose that interplay between CaM and SMP30 regulates Akt activity, and thus SMP30 acts as a survival factor in hepatocytes.

Linking Mass Spectrometry and Slab-Polyacrylamide Gel Electrophoresis by Passive Elution of Lipopolysaccharides from Reverse-Stained Gels: Analysis of Gel-Purified Lipopolysaccharides from Haemophilus influenzae Strain Rd

Haemophilus influenzae is an important cause of human disease, and its lipopolysaccharide (LPS) is known to be a major virulence factor. H. influenzae produces short-chain LPS of which the heterogeneity is often visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) using silver staining for detection. Individual bands have not previously been recovered by this method in quantities sufficient for mass spectrometry. In an attempt toward the development of sensitive mass spectrometrical strategies to be used in structural studies of H. influenzae LPS and LPS from other bacteria, we have applied here our previously described slab-PAGE-based micropurification method to obtain unmodified LPS fractions of high purity (>95%) from a crude LPS preparation of H. influenzae strain Rd. Two LPS-fractions were obtained which, after a procedure including mild acid hydrolysis, dephosphorylation, and permethylation of the resulting oligosaccharides, were subjected to tandem electrospray ionization mass spectrometry (ESI-MS/MS). The quantities of micropurified LPS fractions-the recovery of LPS in terms of total mass was 30%-were found sufficient to allow the characterization of LPS glycoforms. The ESI-MS spectra of the individual bands showed reduced heterogeneity. Furthermore, the integrity of the micropurified LPS was confirmed. The spectra-displayed molecular ions showed improved intensity, increased respective signal-to-noise ratios demonstrating the sensitivity of analysis. Consequently, both the direct determination of the molecular masses of the gel-separated LPS glycoforms and sequence analyses using ESI-MS/MS were possible.

Detection technologies in proteome analysis

Common strategies employed for general protein detection include organic dye, silver stain, radiolabeling, reverse stain, fluorescent stain, chemiluminescent stain and mass spectrometry-based approaches. Fluorescence-based protein detection methods have recently surpassed conventional technologies such as colloidal Coomassie blue and silver staining in terms of quantitative accuracy, detection sensitivity, and compatibility with modern downstream protein identification and characterization procedures, such as mass spectrometry. Additionally, specific detection methods suitable for revealing protein post-translational modifications have been devised over the years. These include methods for the detection of glycoproteins, phosphoproteins, proteolytic modifications, S-nitrosylation, arginine methylation and ADP-ribosylation. Methods for the detection of a range of reporter enzymes and epitope tags are now available as well, including those for visualizing beta-glucuronidase, beta-galactosidase, oligohistidine tags and green fluorescent protein. Fluorescence-based and mass spectrometry-based methodologies are just beginning to offer unparalleled new capabilities in the field of proteomics through the performance of multiplexed quantitative analysis. The primary objective of differential display proteomics is to increase the information content and throughput of proteomics studies through multiplexed analysis. Currently, three principal approaches to differential display proteomics are being actively pursued, difference gel electrophoresis (DIGE), multiplexed proteomics (MP) and isotope-coded affinity tagging (ICAT). New multiplexing capabilities should greatly enhance the applicability of the two-dimensional gel electrophoresis technique with respect to addressing fundamental questions related to proteome-wide changes in protein expression and post-translational modification.

Mass measurements of C-terminally truncated alpha-crystallins from two-dimensional gels identify Lp82 as a major endopeptidase in rat lens

Molecular chaperone activity of lens alpha-crystallins is reduced by loss of the C terminus. The purpose of this experiment was to 1) determine the cleavage sites produced in vitro by ubiquitous m-calpain and lens-specific Lp82 on alpha-crystallins, 2) identify alpha-crystallin cleavage sites produced in vivo during maturation and cataract formation in rat lens, and 3) estimate the relative activities of Lp82 and m-calpain by appearance of protease-specific cleavage products in vivo. Total soluble protein from young rat lens was incubated with recombinant m-calpain or Lp82 and 2 mM Ca2+. Resulting fragmented alpha-crystallins were separated by two-dimensional gel electrophoresis. Eluted alpha-crystallin spots were analyzed by mass spectrometry. Cleavage sites on insoluble alpha-crystallins were determined similarly in mature rat lens nucleus and in cataractous rat lens nucleus induced by selenite. In vitro proteolysis of alphaA-crystallin by Lp82 and m-calpain produced unique cleavage sites by removing 5 and 11 residues, respectively, from the C terminus. In vivo, the protease-specific truncations removing 5 and 11 residues from alphaA were both found in maturing lens, whereas only the truncation removing 5 residues was found in cataractous lens. Other truncation sites, common to both calpain isoforms, resulted from the removal of 8, 10, 16, 17, and 22 residues from the C terminus of alphaA. Using uniquely truncated alphaA-crystallins as in vivo markers, Lp82 and m-calpain were both found to be active during normal maturation of rat lens, whereas Lp82 seemed especially active during selenite cataract formation. These C-terminal truncations decrease chaperone activity of alpha-crystallins, possibly leading to the observed increases in insoluble proteins during aging and cataract. The methodology that allowed accurate mass measurements of proteins eluted from 2D gels should be useful to examine rapidly other post-translational modifications.

Detection of biomolecules in electrophoresis gels with salts of imidazole and zinc II: a decade of research

The proven ability of gel electrophoresis to simultaneously resolve, in a single experiment, many components from complex biological samples, has determined its preference over a variety of well-established chromatographic methods. Therefore, procedures placed at the interface between gel separation and microanalysis have earned increasing significance with respect to the overall success of the microanalytical strategy. The first of these procedures is the detection technique. The most important requirement for compatibility with further analysis or bioapplications is that the staining method does not compromise the chemical integrity and the biological properties of micropurified biomolecules. Procedures for negative detection of proteins with metal salts that have been proven to comply with this condition have been known for about 15 years. Only recently have these procedures been extended to the field of nucleic acids and lipopolysaccharides. The focus of this review is to chronicle the development and current status of the negative or reverse stain procedure based on the in-gel reaction of imidazole with zinc salts and its applications forthe micropurification and analysis of unmodified proteins, nucleic acids and bacterial lipopolysaccharides. We highlight the common aspects in the detection of the three types of biomolecules, and their applications to structural and biological analyses. Emphasis is given on the mechanism underlying imidazole-zinc staining, as it contributes to a deeper understanding of a general detection mechanism with metal salts. Finally, we discuss the latest applications of the techniques in proteomics and their possible impact on the characterization of gel-separated single components from complex lipopolysaccharides.

Proteome mapping by two-dimensional polyacrylamide gel electrophoresis in combination with mass spectrometric protein sequence analysis

The high resolving power of two-dimensional polyacrylamide gel electrophoresis 2D-PAGE and its full analytical and preparative potential have been described with special emphasis on reproducibility and standardization of protein spot patterns, enhanced protein detection sensitivity, and computer analysis database development. New methodologies for peptide mass fingerprinting, peptide, sequence, and fragmentation tagging have been highlighted. Major challenges associated with 2D-PAGE/mass spectrometric protein sequencing were outlined which need to be addressed in the future, including sample enrichment, use of alternative gel matrices, improvements in separation systems interfaced directly to the mass spectrometer, and design of high-sensitivity instruments with very high mass ranges. It is hoped that comparative studies to identify, quantitate, and characterize proteins differentially expressed in normal versus diseased cells would give insight into mechanisms of pathogenesis and allow the development of a way to control both the etiology and the course of diseases.

A thousand points of light: the application of fluorescence detection technologies to two-dimensional gel electrophoresis and proteomics

As proteomics evolves into a high-throughput technology for the study of global protein regulation, new demands are continually being placed upon protein visualization and quantitation methods. Chief among these are increased detection sensitivity, broad linear dynamic range and compatibility with modern methods of microchemical analyses. The limitations of conventional protein staining techniques are increasingly being encountered as high sensitivity electrophoresis methods are interfaced with automated gel stainers, image analysis workstations, robotic spot excision instruments, protein digestion work stations, and mass spectrometers. Three approaches to fluorescence detection of proteins in two-dimensional (2-D) gels are currently practiced: covalent derivatization of proteins with fluorophores, intercalation of fluorophores into the sodium dodecyl sulfate (SDS) micelle, and direct electrostatic interaction with proteins by a Coomassie Brilliant Blue-type mechanism. This review discusses problems encountered in the analysis of proteins visualized with conventional stains and addresses advances in fluorescence protein detection, including immunoblotting, as well as the use of charge-coupled device (CCD) camera-based and laser-scanner-based image acquisition devices in proteomics.

Post-translational modification of p53 protein in response to ionizing radiation analyzed by mass spectrometry

The p53 tumor suppressor protein promotes cell cycle arrest or apoptosis in response to DNA damage and other forms of stress. p53 protein functions as a transcription factor by binding to specific DNA sequences and regulating the transcription of target genes. This activity of p53 is reported to be regulated by phosphorylation and acetylation occuring at various sites on the molecule. Here, we have used a direct and non-radioactive approach involving mass spectrometric analysis of p53 protein to identify sites that are covalently modified in vivo, either constitutively or in response to ionizing radiation. Following partial purification by immuno-affinity chromatography and enzymatic in-gel digestion, the resulting p53 peptides were analyzed by MALDI-TOF and nanoelectrospray mass spectrometry. Mass spectrometry analyses identified four sites at the N terminus that were phosphorylated in response to irradiation, a single constitutive phosphorylation site at serine 315 and several acetylation sites.

Applications of mass spectrometry to signal transduction

Advances in mass spectrometry instrumentation, protocols for sample handling, and computational methods provide powerful new approaches to solving problems in analytical biochemistry. This review summarizes recent work illustrating ways in which mass spectrometry has been used to address questions relevant to signal transduction. Rather than encompass all of the instruments or methodologies that might be brought to bear on these problems, we present an overview of commonly used techniques, promising new methodologies, and some applications.

Proteome analysis of polyacrylamide gel-separated proteins visualized by reversible negative staining using imidazole-zinc salts

Identification and characterization of proteins isolated from natural sources by polyacrylamide gel electrophoresis has become a routine technique. However, efficient sample proteolysis and subsequent peptide extraction is still problematic. Here, we present an improved protocol for the rapid detection of polyacrylamide gel-separated proteins, in situ protein modification, proteolytic digestion and peptide extraction for subsequent protein identification and characterization by capillary high-performance liquid chromatography/tandem mass spectrometry. This simple technique employs the rapid imidazole-zinc reverse stain, in-gel S-pyridylethylation and proteolytic digestion of microcrushed polyacrylamide gel pieces with proteases. This technique obviates the need for buffer exchange or gel lyophilisation due to all of the sample manipulation steps being carried out at near neutral pH and thus lends itself readily to automation.

Elution of lipopolysaccharides from polyacrylamide gels

A simple procedure for elution in water of bacterial lipopolysaccharides (LPS) from sodium dodecyl sulfate-polyacrylamide gels is described. It consists of the combination of three principal steps: first, highly sensitive on-gel LPS detection (1-10 ng/band) with zinc-imidazole (negative or reverse staining); second, washing of the individual LPS band in a solution of a zinc-complexing agent (e.g., 100 mM EDTA); and finally, elution of the LPS (100-200 microliters water for a 0.5-microgram LPS band) from gel microparticles for 3 h at room temperature. Using this procedure, we have successfully eluted a variety of LPS forms from Bordetella pertussis, Escherichia coli 0111:B4, E. coli K-235, Salmonella enteritidis, and Pseudomonas aeruginosa. Elution recovery of rough or semismooth LPS was about 70-80%, while that of smooth LPS was only about 10%. Eluted LPS was biologically active as tested by limulus amebocyte lysate and TNF-alpha assays.