Substrates Modulate Charge-Reorganization Allosteric Effects in Protein-Protein Association

Protein function may be modulated by an event occurring far away from the functional site, a phenomenon termed allostery. While classically allostery involves conformational changes, we recently observed that charge redistribution within an antibody can also lead to an allosteric effect, modulating the kinetics of binding to target antigen. In the present work, we study the association of a polyhistidine tagged enzyme (phosphoglycerate kinase, PGK) to surface-immobilized anti-His antibodies, finding a significant Charge-Reorganization Allostery (CRA) effect. We further observe that PGK's negatively charged nucleotide substrates modulate CRA substantially, even though they bind far away from the His-tag-antibody interaction interface. In particular, binding of ATP reduces CRA by more than 50%. The results indicate that CRA is affected by the binding of charged molecules to a protein and provide further insight into the significant role that charge redistribution can play in protein function.

Polydisperse molecular architecture of connexin 26/30 heteromeric hemichannels revealed by atomic force microscopy imaging

Connexin (Cx) protein forms hemichannels and gap junctional channels, which play diverse and profound roles in human physiology and diseases. Gap junctions are arrays of intercellular channels formed by the docking of two hemichannels from adjacent cells. Each hexameric hemichannel contains the same or different Cx isoform. Although homomeric Cxs forms have been largely described functionally and structurally, the stoichiometry and arrangement of heteromeric Cx channels remain unknown. The latter, however, are widely expressed in human tissues and variation might have important implications on channel function. Investigating properties of heteromeric Cx channels is challenging considering the high number of potential subunit arrangements and stoichiometries, even when only combining two Cx isoforms. To tackle this problem, we engineered an HA tag onto Cx26 or Cx30 subunits and imaged hemichannels that were liganded by Fab-epitope antibody fragments via atomic force microscopy. For Cx26-HA/Cx30 or Cx30-HA/Cx26 heteromeric channels, the Fab-HA binding distribution was binomial with a maximum of three Fab-HA bound. Furthermore, imaged Cx26/Cx30-HA triple liganded by Fab-HA showed multiple arrangements that can be derived from the law of total probabilities. Atomic force microscopy imaging of ringlike structures of Cx26/Cx30-HA hemichannels confirmed these findings and also detected a polydisperse distribution of stoichiometries. Our results indicate a dominant subunit stoichiometry of 3Cx26:3Cx30 with the most abundant subunit arrangement of Cx26-Cx26-Cx30-Cx26-Cx30-Cx30. To our knowledge, this is the first time that the molecular architecture of heteromeric Cx channels has been revealed, thus providing the basis to explore the functional effect of these channels in biology.

[Preparation of monoclonal antibodies against His-tag and epitope analysis of cross antigens]

OBJECTIVE

To explore the influence of His-tag on recombinant proteins in vaccination, immunization and pathogenesis.

METHODS

Multiple mouse monoclonal antibodies (mAb) against His-tag were prepared. The biological and immunoreactive characteristics of these mAbs and their cross-reactivity with the normal human tissues were investigated by ELISA, Western blotting and immunohistochemistry (IHC), respectively.

RESULTS

The binding activity of these anti-His mAbs was associated with the steric configuration of the his-tagged antigen. In addition, most of these mAbs reacted with human hemoglobin and some normal human tissues.

CONCLUSION

Anti-His antibodies could be elicited by His-tagged recombinant proteins in vivo experiments. Moreover, the functional studies of the His-tagged recombinant proteins might be affected by the reactions of anti-His6 antibodies with human hemoglobin and normal human tissues.

MD-2 determinants of nickel and cobalt-mediated activation of human TLR4

Recent findings unexpectedly revealed that human TLR4 can be directly activated by nickel ions. This activation is due to the coordination of nickel by a cluster of histidine residues on the ectodomain of human TLR4, which is absent in most other species. We aimed to elucidate the role of MD-2 in the molecular mechanism of TLR4/MD-2 activation by nickel, as nickel binding site on TLR4 is remote from MD-2, which directly binds the endotoxin as the main pathological activator of TLR4. We identified MD-2 and TLR4 mutants which abolished TLR4/MD-2 receptor activation by endotoxin but could nevertheless be significantly activated by nickel, which acts in synergy with LPS. Human TLR4/MD-2 was also activated by cobalt ions, while copper and cadmium were toxic in the tested concentration range. Activation of TLR4 by cobalt required MD-2 and was abolished by human TLR4 mutations of histidine residues at positions 456 and 458. We demonstrated that activation of TLR4 by nickel and cobalt ions can trigger both the MyD88-dependent and the -independent pathway. Based on our results we propose that predominantly hydrophobic interactions between MD-2 and TLR4 contribute to the stabilization of the TLR4/MD-2/metal ion complex in a conformation that enables activation.

Vaccination against Streptococcus pneumoniae using truncated derivatives of polyhistidine triad protein D

Polyhistidine triad protein D (PhtD) has been described as a promising vaccine candidate for use against Streptococcus pneumoniae, but there has been a lack of examination of its structure and of which region(s) of the protein are targeted by protective immune responses. In this study, we purified recombinant truncated derivatives of PhtD and examined their secondary structural composition, as well as their capacity to bind antibodies from polyclonal murine serum generated against the full length protein. This allowed the identification of a particularly immunogenic fragment of PhtD, which was also purified and characterised. The truncated derivatives were tested as vaccine antigens in mouse models of pneumococcal sepsis and colonisation, using alum and E. coli heat labile toxin B subunit respectively as adjuvants. These experiments revealed that whilst the immunogenic region identified may be a promising candidate to protect against sepsis, the full length PhtD was ineffective at conferring significant protective immunity. These results are significant for the potential for PhtD to be used in novel vaccines, which are currently being tested in clinical trials.

A sulfhydryl-reactive ruthenium (II) complex and its conjugation to protein G as a universal reagent for fluorescent immunoassays

To develop a fluorescent ruthenium complex for biosensing, we synthesized a novel sulfhydryl-reactive compound, 4-bromophenanthroline bis-2,2′-dipyridine Ruthenium bis (hexafluorophosphate). The synthesized Ru(II) complex was crosslinked with thiol-modified protein G to form a universal reagent for fluorescent immunoassays. The resulting Ru(II)-protein G conjugates were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The emission peak wavelength of the Ru(II)-protein G conjugate was 602 nm at the excitation of 452 nm which is similar to the spectra of the Ru(II) complex, indicating that Ru(II)-protein G conjugates still remain the same fluorescence after conjugation. To test the usefulness of the conjugate for biosensing, immunoglobulin G (IgG) binding assay was conducted. The result showed that Ru(II)-protein G conjugates were capable of binding IgG and the more cross-linkers to modify protein G, the higher conjugation efficiency. To demonstrate the feasibility of Ru(II)-protein G conjugates for fluorescent immunoassays, the detection of recombinant histidine-tagged protein using the conjugates and anti-histidine antibody was developed. The results showed that the histidine-tagged protein was successfully detected with dose-response, indicating that Ru(II)-protein G conjugate is a useful universal fluorescent reagent for quantitative immunoassays.

Conversion of scFv peptide-binding specificity for crystal chaperone development

In spite of advances in protein expression and purification over the last decade, many proteins remain recalcitrant to structure determination by X-ray crystallography. One emerging tactic to obtain high-quality protein crystals for structure determination, particularly in the case of membrane proteins, involves co-crystallization with a protein-specific antibody fragment. Here, we report the development of new recombinant single-chain antibody fragments (scFv) capable of binding a specific epitope that can be introduced into internal loops of client proteins. The previously crystallized hexa-histidine-specific 3D5 scFv antibody was modified in the complementary determining region and by random mutagenesis, in conjunction with phage display, to yield scFvs with new biochemical characteristics and binding specificity. Selected variants include those specific for the hexa-histidine peptide with increased expression, solubility (up to 16.6 mg/ml) and sub-micromolar affinity, and those with new specificity for the EE hexa-peptide (EYMPME) and nanomolar affinity. Complexes of one such chaperone with model proteins harboring either an internal or a terminal EE tag were isolated by gel filtration. The 3.1 Å resolution structure of this chaperone reveals a binding surface complementary to the EE peptide and a ∼52 Å channel in the crystal lattice. Notably, in spite of 85% sequence identity, and nearly identical crystallization conditions, the engineered scFv crystallizes in a different space group than the parent 3D5 scFv, and utilizes two new crystal contacts. These engineered scFvs represent a new class of chaperones that may eliminate the need for de novo identification of candidate chaperones from large antibody libraries.

Improved method to raise polyclonal antibody using enhanced green fluorescent protein transgenic mice

Recombinant fusion protein is widely used as an antigen to raise antibodies against the epitope of a target protein. However, the concomitant anticarrier antibody in resulting antiserum reduces the production of the desired antibody and brings about unwanted non-specific immune reactions. It is proposed that the carrier protein transgenic animal could be used to solve this problem. To validate this hypothesis, enhanced green fluorescent protein (EGFP) transgenic mice were produced. By immunizing the mice with fusion protein His6HAtag-EGFP, we showed that the antiserum from the transgenic mice had higher titer antibody against His6HA tag and lower titer antibody against EGFP compared with that from wild-type mice. Therefore, this report describes an improved method to raise high titer antipeptide polyclonal antibody using EGFP transgenic mice that could have application potential in antibody preparation.

Oriented immobilisation of anti-pneumolysin Fab through a histidine tag for electrochemical immunosensors

Orientation of reagents is a key step in the construction of immunosensors. When the immunoreagent is a recombinant protein, this can be achieved by employing hexahistidine tags. The orientation of recombinant histidine-tagged Fab fragments of monoclonal anti-pneumolysin antibodies on gold films is evaluated. Using histidine as a chelator of Ni or employing an anti-polyhistidine antibody for capturing the His6 residue is considered. Measurements are based in the signal of indigo, which comes from the hydrolysis of 3-indoxylphosphate by alkaline phosphatase (AP). The attachment of the enzyme occurs through the interaction of biotin with AP-labelled streptavidin or employing AP-conjugated immunoreagents. In the case of the interaction Ni-histidine, for the study of the self-assembling process a His-tagged and biotinylated protein (His6-GST-B) was employed. General conditions were studied and non-specific adsorption was avoided with the use of 1-hexanethiol. Improvements of the signal compared with the direct adsorption were only achieved by the use of histidine capturing antibodies. With an optimised ratio anti-polyhis:His6-Fab the signal increases approximately a 100%. Precision is adequate and the response is linear with the concentration of pneumolysin between 0.1 and 10 ng/mL.

Diagnostic potential of recombinant protein of hexahistidine tag and infectious bursal disease virus VPX expressed in Escherichia coli

The current method to detect antibody titre against infectious bursal disease virus (IBDV) in chickens is based on enzyme-linked immunosorbent assay (ELISA) using whole virus as coating antigen. Coating the ELISA plates requires a purified or at least semi-purified preparation of virus as antigen, which needs special skills and techniques. In this study, instead of using whole virus, recombinant protein of hexahistidine tag (His 6 tag) and VPX protein of IBDV expressed in E. coli was used as an alternative antigen to coat the ELISA plates. There was a good correlation coefficient (R2 = 0.972) between the results of the ELISA using plates coated with monoclonal antibody against His 6 tag and those of the commercial IBDV ELISA kit. Hence, His 6 tag and VPX recombinant protein expressed in E. coli has the potential for the development of ELISA for the measurement of IBDV-specific antibody.

Enzyme-linked immunosorbent assays for insulin-like growth factor-I using six-histidine tag fused proteins

The fusion proteins of insulin-like growth factor-I (IGF-I) and six-histidine tag (IGF-I-6H, 6H-IGF-I-6H) were cloned, expressed, purified and renatured, with their immunoreaction properties and biological activities intact. The binding kinetics between these fusion proteins and anti-IGF-I antibody or anti-6H antibody were studied using surface plasmon resonance (SPR). Two enzyme-linked immunosorbent assay (ELISA) modes, which proved feasible in the measurement of human serum samples, were used to detect IGF-I with the help of the six-histidine tagged proteins. Furthermore, combining the production technique of the six-histidine tagged fusion protein with the competitive sandwich ELISA mode, using an enzyme labeled anti-6H antibody as a tracer, can be a universal immunochemical method to quantitate other polypeptides or proteins.

Binding Characteristics of IFN-alpha Subvariants to IFNAR2-EC and Influence of the 6-Histidine Tag

The expression, purification, detection, and assay of recombinant proteins have been made more convenient and rapid by the use of small affinity tags. To facilitate the purification of interferon-alpha2c (IFN-alpha2c) by metal chelate affinity chromatography, N-terminal 6-histidine tag was introduced via genetic manipulation. Two preparations of IFN material were purified; one contained IFN-alpha2c with the 6-histidine tag, and the other contained IFN-alpha2c without the 6-histidine tag. The antigenic properties of the human IFN-alpha2c subvariant with and without the 6-histidine tag, as well as the effects of the N-terminal 6-histidine tag on IFN-alpha2c interaction with the extracellular domain of human IFN-alpha receptor chain 2 (IFNAR2-EC) were examined. For the purposes of this study, IFNs were characterized by Western blots with anti-IFN monoclonal antibodies (mAb) and bioassays. Immunoblot analyses showed differences between IFN-alpha2c-6-histidine tag and IFN-alpha2a, b, c in their interaction with IFNAR2-EC. We also observed differences between IFN-alpha2c-6-histidine tag and IFN-alpha2a, b, c in bioactivities. This study is the first report that shows that an N-terminal 6-histidine tag on IFN-alpha2c can affect its interaction with receptor and cause a different bioactivity.

Template switching within exons 3 and 4 of KV11.1 (HERG) gives rise to a 5' truncated cDNA

K(V)11.1 (HERG) channels contribute to membrane potential in a number of excitable cell types. We cloned a variant of K(V)11.1 from human jejunum containing a 171 bp deletion spanning exons 3 and 4. Expression of a full-length cDNA clone containing this deletion gave rise to protein that trafficked to the cell membrane and generated robust currents. The deletion occurred in a G/C-rich region and identical sequence elements of UGGUGG were located at the deletion boundaries. In recent studies these features have been implicated to cause deletions via template switching during cDNA synthesis. To examine this possibility we compared cDNAs from human brain, heart, and jejunum synthesized at lower (42 degrees C) and higher temperatures (70 degrees C). The 171 bp deletion was absent at the higher temperature. Our results suggest that the sequence and secondary structure of mRNA in the G/C rich region leads to template switching producing a cDNA product with a 171 bp deletion.

Recombinant tegumental protein Shistosoma japonicum very lowdensity lipoprotein binding protein as a vaccine candidate against Schistosoma japonicum

A polyhistidine-tagged recombinant tegumental protein Schistosoma japonicum very lowdensity lipoprotein binding protein (SVLBP) from adult Schistosoma japonicum was expressed in Escherichia coli. The affinity purified rSVLBP was used to vaccinate mice. The worm numbers and egg deposition recovered from the livers and veins of the immunized mice were 33.5% and 47.6% less than that from control mice, respectively (p<0.05). There was also a marked increase in the antibody response in vaccinated mice: the titer of IgG1 and IgG2a, IgG2b in the vaccinated group was significantly higher than that in the controls (>1:6,400 in total IgG). In a comparison of the reactivity of sera from healthy individuals and patients with rSVLBP, recognition patterns against this parasite tegumental antigen varied among different groups of the individuals. Notably, the average titres of anti-rSVLBP antibody in sera from faecal egg-negative individuals was significantly higher than that in sera from the faecal egg-positives, which may be reflect SVLBP-specific protection. These results suggested that the parasite tegumental protein SVLBP was a promising candidate for further investigation as a vaccine antigen for use against Asian schistosomiasis.

Epitope mapping using mRNA display and a unidirectional nested deletion library

In vitro selection targeting an anti-polyhistidine monoclonal antibody was performed using mRNA display with a random, unconstrained 27-mer peptide library. After six rounds of selection, epitope-like peptides were identified that contain two to five consecutive, internal histidines and are biased for arginine residues, without any other identifiable consensus. The epitope was further refined by constructing a high-complexity, unidirectional fragment library from the final selection pool. Selection by mRNA display minimized the dominant peptide from the original selection to a 15-residue functional sequence (peptide Cmin: RHDAGDHHHHHGVRQ; K(D) = 38 nM). Other peptides recovered from the fragment library selection revealed a separate consensus motif (ARRXA) C-terminal to the histidine track. Kinetics measurements made by surface plasmon resonance, using purified Fab (antigen-binding fragment) to prevent avidity effects, demonstrate that the selected peptides bind with 10- to 75-fold higher affinities than a hexahistidine peptide. The highest affinity peptides (K(D) approximately 10 nM) encode both a short histidine track and the ARRXA motif, suggesting that the motif and other flanking residues make important contacts adjacent to the core polyhistidine-binding site and can contribute >2.5 kcal/mol of binding free energy. The fragment library construction methodology described here is applicable to the development of high-complexity protein or cDNA expression libraries for the identification of protein-protein interaction domains.

Mutational analysis of histidine residues in human organic anion transporter 4 (hOAT4)

Human organic anion transporter 4 (hOAT4) belongs to a family of organic anion transporters which play critical roles in the body disposition of clinically important drugs, including anti-HIV therapeutics, antitumour drugs, antibiotics, anti-hypertensives and anti-inflammatories. hOAT4-mediated transport of the organic anion oestrone sulphate in COS-7 cells was inhibited by the histidine-modifying reagent DEPC (diethyl pyrocarbonate). Therefore the role of histidine residues in the function of hOAT4 was examined by site-directed mutagenesis. All five histidine residues of hOAT4 were converted into alanine, singly or in combination. Single replacement of His-47, or simultaneous replacement of His-47/52/83 or His-47/52/83/305/469 (H-less) led to a 50-80% decrease in transport activity. The decreased transport activity of these mutants was correlated with a decreased amount of cell-surface expression, although the total cell expression of these mutants was similar to that of wild-type hOAT4. These results suggest that mutation at positions 47, 47/52/83 and 47/52/83/305/469 impaired membrane expression rather than function. We also showed that, although most of the histidine mutants of hOAT4 were sensitive to inhibition by DEPC, H469A (His-469-->Ala) was completely insensitive to inhibition by this reagent. Therefore modification of His-469 is responsible for the inhibition of hOAT4 by DEPC.

Flow cytometric determination of FcγRIIa (CD32) polymorphism

A guanine to adenine point mutation results in an arginine (R) to histidine (H) substitution in FcgammaRIIa at residue 131 that strongly impacts receptor function. This FcgammaRIIa polymorphism is mostly typed by allele-specific polymerase chain reactions (PCR) or in functional assays, dependent on ligand binding. Both types of methods are laborious, time consuming, and not readily available in routine laboratories. We generated a panel of human antibodies against FcgammaRII, and one of them, MDE-9, selectively recognized the FcgammaRIIa-H131 allotype. MDE-9 was applicable to detect FcgammaRIIa-H131 in both flow cytometry and immunohistochemistry. MDE-9 was used to develop an FcgammaRIIa allotyping method based on flow cytometry. In a "single-tube assay", FITC-labeled MDE-9 (specific for FcgammaRIIa-H131) and Cy3-labeled mAb 41H16 (specific for FcgammaRIIa-R131) were added to 50 mul samples of whole blood. The results of flow cytometric FcgammaRIIa allotyping correlated completely with PCR genotyping. This novel allotyping assay should facilitate the screening of patients in a routine diagnostic setting. In addition, a combination of MDE-9 and 41H16 can be used in FcgammaRIIa-H/H131 homozygous individuals to detect FcgammaRIIa and FcgammaRIIb surface expression on monocytes. This is an important application of these antibodies because, to this day, no antibodies were available to specifically study the surface expression of FcgammaRIIb.

Structural genomics for Caenorhabditis elegans: high throughput protein expression analysis

The structural genomics initiatives have begun with the aim to create a so-called "basic set library" of protein folds that will be used to improve protein prediction methods. Such a library is thought to require the determination of up to 10,000 new structures, including representative structures of several sequence variants from each protein fold. To meet this goal in a reasonable time frame and cost, automated systems must be utilized to clone and to identify the soluble recombinant proteins contained in multiple genomes. This paper presents such a system, developed using the genome of Caenorhabditis elegans (19,099 genes) as a model eukaryotic organism for structural genomics. This system successfully automates nearly all aspects of recombinant protein expression analysis including subcloning, bacterial growth, recombinant protein expression, protein purification, and scoring protein solubility.

Protein Microarray System for Detecting Protein−Protein Interactions Using an Anti-His-Tag Antibody and Fluorescence Scanning: Effects of the Heme Redox State on Protein−Protein Interactions of Heme-Regulated Phosphodiesterase from Escherichia coli

A highly sensitive microarray system for detecting protein-protein interactions has been developed. This method was successfully applied to analyze the interactions of heme-regulated phosphodiesterase from Escherichia coli (Ec DOS). To immobilize (His)6-Tag fused Ec DOS, anti-(His)6-Tag monoclonal antibody (anti-(His)6-Tag mAb) was initially immobilized on the solid surface, and (His)6-Tag fused Ec DOS was fixed by antigen-antibody interactions. For this experiment, ProteoChip, generally suitable for antibody immobilization, was used as solid substrate. In this report, we confirm the antibody immobilization ability of ProteoChip and specific binding to the F(c) region of the antibody. Based on this finding, interdomain interactions between Ec DOS and the isolated heme-bound PAS domain were investigated on the solid surface. Ec DOS immobilized via anti-(His)6-Tag mAb maintained interactions with the PAS fragment, in contrast to directly immobilized Ec DOS in the absence of anti-(His)6-Tag mAb. Heme-redox-sensitive interactions between Ec DOS and the PAS fragment were additionally detected using anti-(His)6-Tag mAb as a mediator. Our results collectively suggest that the immobilization method using anti-Tag antibody is suitable for maintaining native protein characteristics to facilitate elucidation of their structures and functions on solid surfaces.

An improved method for the in vitro evolution of aptamers and applications in protein detection and purification

One of the key components of proteomics initiatives is the production of high affinity ligands or probes that specifically recognize protein targets in assays that detect and capture proteins of interest. Particularly versatile probes with tremendous potential for use as affinity molecules are aptamers. Aptamers are short single-stranded DNA or RNA sequences that are selected in vitro based on affinity for a target molecule. Aptamers offer advantages over traditional antibody-based affinity molecules in their ease of production, regeneration and stability, largely due to the chemical properties of nucleic acids versus amino acids. We describe an improved in vitro selection protocol that relies on magnetic separations for DNA aptamer production that is relatively easy and scalable without the need for expensive robotics. We demonstrate the ability of aptamers that recognize thyroid transcription factor 1 (TTF1) to bind their target protein with high affinity and specificity, and detail their uses in a number of assays. The TTF1 aptamers were characterized using surface plasmon resonance, and shown to be useful for enzyme-linked assays, western blots and affinity purification.

N-methacryloly-(L)-histidinemethylester carrying a pseudospecific affinity sorbent for immunoglobulin-G isolation from human plasma in a column system

N-methacryloly-(L)-histidinemethylester (MAH) as a pseudospecific ligand was synthesized by using methacryloyl chloride and histidine. Spherical beads with an average size of 63-75 microm were obtained by suspension polymerization of ethylene glycol dimethacrylate (EGDMA), 2-hydroxyethyl methacrylate (HEMA) and MAH conducted in an aqueous dispersion medium. The specific surface area of the beads was found to be 18.3 m2/g. Poly(EGDMA-HEMA-MAH) beads were used in the separation of immunoglobulin-G (HIgG) from aqueous solutions and/or human plasma in a packed-bed column system. HIgG adsorption capacity of the beads decreased with an increase in the flow-rate of plasma. The maximum HIgG adsorption on the poly(EGDMA-HEMA-MAH) sorbents was observed at pH 7.4. HIgG adsorption onto the poly(EGDMA-HEMA) sorbents was negligible. Higher adsorption values (up to 135 mg/g) were obtained when the poly(EGDMA-HEMA-MAH) sorbents were used from aqueous solutions. HIgG adsorption increased with decreasing temperature and the maximum adsorption achieved at 4 degrees C. MAH incorporation significantly affected HIgG adsorption capacity (135 mg/g). Higher amounts of HIgG were adsorbed from human plasma (up to 165 mg/g). Adsorption capacities of other blood proteins were obtained as 8.7 mg/g for fibrinogen and 14.6 mg/g for albumin. The total protein adsorption was determined as 191 mg/g. The pseudospecific affinity beads allowed one-step separation of HIgG from human plasma. HIgG molecules could be repeatedly adsorbed and desorbed with these sorbents without noticeable loss in their HIgG adsorption capacity.

Crystal structure of the anti-His tag antibody 3D5 single-chain fragment complexed to its antigen

The crystal structure of a mutant form of the single-chain fragment (scFv), derived from the monoclonal anti-His tag antibody 3D5, in complex with a hexahistidine peptide has been determined at 2.7 A resolution. The peptide binds to a deep pocket formed at the interface of the variable domains of the light and the heavy chain, mainly through hydrophobic interaction to aromatic residues and hydrogen bonds to acidic residues. The antibody recognizes the C-terminal carboxylate group of the peptide as well as the main chain of the last four residues and the last three imidazole side-chains. The crystals have a solvent content of 77% (v/v) and form 70 A-wide channels that would allow the diffusion of peptides or even small proteins. The anti-His scFv crystals could thus act as a framework for the crystallization of His-tagged target proteins. Designed mutations in framework regions of the scFv lead to high-level expression of soluble protein in the periplasm of Escherichia coli. The recombinant anti-His scFv is a convenient detection tool when fused to alkaline phosphatase. When immobilized on a matrix, the antibody can be used for affinity purification of recombinant proteins carrying a very short tag of just three histidine residues, suitable for crystallization. The experimental structure is now the basis for the design of antibodies with even higher stability and affinity.

Multiple sites of L-histidine decarboxylase expression in mouse suggest novel developmental functions for histamine

Histamine mediates many types of physiologic signals in multicellular organisms. To clarify the developmental role of histamine, we have examined the developmental expression of L-histidine decarboxylase (HDC) mRNA and the production of histamine during mouse development. The predominant expression of HDC in mouse development was seen in mast cells. The HDC expression was evident from embryonal day 13 (Ed13) until birth, and the mast cells were seen in most peripheral tissues. Several novel sites with a prominent HDC mRNA expression were revealed. In the brain, the choroid plexus showed HDC expression at Ed14 and the raphe neurons at Ed15. Close to the parturition, at Ed19, the neurons in the tuberomammillary (TM) area and the ventricular neuroepithelia also displayed a clear HDC mRNA expression and histamine immunoreactivity (HA-ir). From Ed14 until birth, the olfactory and nasopharyngeal epithelia showed an intense HDC mRNA expression and HA-ir. In the olfactory epithelia, the olfactory receptor neurons (ORN) were shown to have very prominent histamine immunoreactivity. The bipolar nerve cells in the epithelium extended both to the epithelial surface and into the subepithelial layers to be collected into thick nerve bundles extending caudally toward the olfactory bulbs. Also, in the nasopharynx, an extensive subepithelial network of histamine-immunoreactive nerve fibers were seen. Furthermore, in the peripheral tissues, the degenerating mesonephros (Ed14) and the convoluted tubules in the developing kidneys (Ed15) showed HDC expression, as did the prostate gland (Ed15). In adult mouse brain, the HDC expression resembled the neuronal pattern observed in rat brain. The expression was restricted to the TM area in the ventral hypothalamus, with the main expression in the five TM subgroups called E1-E5. A distinct mouse HDC mRNA expression was also seen in the ependymal wall of the third ventricle, which has not been reported in the rat. The tissue- and cell-specific expression patterns of HDC and histamine presented in this work indicate that histamine could have cell guidance or regulatory roles in development.

Cloning, overexpression, purification, and immunobiology of an 85-kilodalton outer membrane protein from Haemophilus ducreyi

We have identified an 85-kDa outer membrane protein that is expressed by all tested strains of Haemophilus ducreyi. Studies of related proteins from other pathogenic bacteria, including Haemophilus influenzae, Pasteurella multocida, Neisseria gonorrhoeae, Neisseria meningitidis, and Shigella dysenteriae, suggested a role for these proteins in pathogenesis and immunity. In keeping with the first such described protein from Haemophilus influenzae type B, we termed the H. ducreyi protein D15. The gene encoding the H. ducreyi D15 protein was cloned and sequenced, and the deduced amino acid sequence was found to be most similar to sequences of the D15-related proteins from other Pasteurella spp. The arrangement of the flanking genes was similar to that of H. influenzae Rd and suggested that D15 was part of a multigene operon. Attempts to make a null mutation of the D15 gene were unsuccessful, paralleling results in other D15 gene studies. Overexpression of H. ducreyi D15 in Escherichia coli resulted in a source of recombinant D15 (rD15) from which it was readily purified. rD15 was immunogenic, and it was found that immunization of rabbits with an rD15 vaccine preparation conferred partial protection against a virulent challenge infection. Antisera to an N-terminal peptide recognized all tested strains of H. ducreyi.

Development and evaluation of ELISA procedures to detect antibodies against the major envelope protein (G(L)) of equine arteritis virus

Enzyme-linked immunosorbant assays (ELISAs) were developed for the detection of antibodies against the major envelope glycoprotein (G(L)) of equine arteritis virus (EAV). A 6-Histidine tagged recombinant protein expressing the complete G(L) ectodomain (G(L)-6His), a glutathione-S-transferase recombinant protein expressing amino acids 55-98 of G(L) (G(L)-GST) and an ovalbumin-conjugated synthetic peptide representing amino acids 81-106 of G(L) (G(L)-OVA) were used as diagnostic antigens. An ELISA procedure was developed and optimised for each antigen. The G(L)-OVA and G(L)-6His assays showed the greatest specificity while the G(L)-GST assay was slightly more sensitive that the G(L)-OVA and G(L)-6His assays; results based on the analysis of 50 virus neutralisation positive and 50 virus neutralisation negative sera. The G(L)-OVA ELISA was selected for further evaluation since it was simpler to use than ELISAs based on recombinant antigens and did not suffer from background reactivity. The final sensitivity and specificity of the G(L)-OVA ELISA were 96.75 and 95.6%, respectively, results based on the analysis of 400 virus neutralisation positive and 400 virus neutralisation negative sera. It also detected EAV antibody (100% efficiency) in seropositive shedding stallions and, in ponies infected experimentally with the UK93 isolate of EAV, the appearance of virus neutralising antibodies and G(L)-OVA ELISA-specific immunoglobulins coincided.

Peptide specificity of the Amerindian B*3905 allotype: molecular insight into selection mechanisms driving HLA class I evolution in indigenous populations of the Americas

HLA-B*3905 is apparently restricted to Amerindian populations and presents a wide geographical distribution, from Mexico to Argentina. It differs from B*3901, one of the founder HLA class I alleles of Central and South Amerindians, by a single nucleotide substitution leading to an Asp74Tyr change in the gene product. The peptide specificity of the B*3905 protein was characterized by pool sequence analysis of B*3905-bound peptides and by sequencing of a set of individual ligands, using electrospray ion trap mass spectrometry. The results indicate a double effect of the B*3905 mutation. First, pocket B specificity was shifted towards an increased preference for His at peptide position 2, which is the main anchor for B39-bound peptides, relative to B*3901. Second, at peptide position 3 acidic residues were favored, and aromatic residues disfavored, relative to B*3901. These features approach the peptide specificity of B*3905 to B*3801 and B*1509, allotypes absent from Central and South Amerindians. Together with B*3909, B*3905 is the second HLA-B39 subtype whose polymorphism results in a shift of peptide specificity towards that of HLA-B allotypes absent from these populations. This suggests that HLA-B39 evolution in Central and South America may be an antigen-driven adaptive response, leading to generate antigen-presenting properties absent from the HLA class I repertoire of the ancestral population.

Expression and functional characterization of a pHis-tagged human bradykinin B2 receptor in COS-7 cells

A polyHis-tagged bradykinin (BK) B2 receptor (pHis-BKR) cDNA was constructed and expressed in COS-7 cells. The pHis-BKR is suitable for both immunoprecipitation and immunoblotting with anti-polyHis antibodies and can be easily purified using Ni-NTA columns. Immunochemical detection revealed a molecular mass of approximately 66 kDa. The pHis-BKR is capable of mediating BK-induced stimulation of inositol phosphate formation as well as of mitogen-activated protein kinase (MAPK) activity. Compared with the wild-type receptor (WT-BKR) the tagged receptor showed a slightly enhanced affinity towards BK but a reduced expression level. Despite these modified pharmacological properties the pHis-tagged BKR may be a useful tool for studying BKR modifications and signaling.

Sxa2 is a serine carboxypeptidase that degrades extracellular P-factor in the fission yeast Schizosaccharomyces pombe

Stimulating the fission yeast Schizosaccharomyces pombe with mating pheromones brings about responses that lead to cell conjugation. Persistent stimulation does not, however, induce a continuous response as the cells become desensitized to the presence of the pheromone. One mechanism that contributes to desensitization in M-cells is the release of a carboxypeptidase that inactivates the extracellular P-factor pheromone. Production of the carboxypeptidase requires a functional sxa2 gene. In this study, we report the first molecular characterization of the Sxa2 protein and provide direct evidence that it is the carboxypeptidase that degrades P-factor. Sxa2 is synthesized as a precursor that undergoes an internal cleavage event catalysed by a protease with specificity for basic residues. This generates a series of catalytically active N-terminal fragments and an inactive C-terminal fragment. Cleavage is essential for activation of the carboxypeptidase and, although the C-terminal fragment is inactive, it is required for the N-terminal fragment to attain activity.

Selenoprotein P expression, purification, and immunochemical characterization

Most selenoproteins contain a single selenocysteine residue per polypeptide chain, encoded by an in-frame UGA codon. Selenoprotein P is unique in that its mRNA encodes 10-12 selenocysteine residues, depending on species. In addition to the high number of selenocysteines, the protein is cysteine- and histidine-rich. The function of selenoprotein P has remained elusive, in part due to the inability to express the recombinant protein. This has been attributed to presumed inefficient translation through the selenocysteine/stop codons. Herein, we report for the first time the expression of recombinant rat selenoprotein P in a transiently transfected human epithelial kidney cell line, as well as the endogenously expressed protein from HepG2 and Chinese hamster ovary cells. The majority of the expressed protein migrates with the predicted 57-kDa size of full-length glycosylated selenoprotein P. Based on the histidine-rich nature of selenoprotein P, we have purified the recombinant and endogenously expressed proteins using nickel-agarose affinity chromatography. We show that the recombinant rat and endogenous human proteins react in Western blotting and immunoprecipitation assays with commercial anti-histidine antibodies. The ability to express, purify, and immunochemically detect the recombinant protein provides a foundation for investigating the functions and efficiency of expression of this intriguing protein.

Truncated surface protective antigen (SpaA) of Erysipelothrix rhusiopathiae serotype 1a elicits protection against challenge with serotypes 1a and 2b in pigs

Erysipelothrix rhusiopathiae is a causal agent of swine erysipelas, which is of economic importance in the swine industry by virtue of causing acute septicemia, chronic arthritis, and endocarditis. However, little is known about the genetic properties of its protective antigens. Recently, a surface protective antigen (SpaA) gene was identified from serotype 2 in a mouse model. We cloned spaA from virulent strain Fujisawa (serotype 1a) and determined that the N-terminal 342 amino acids without C-terminal repeats of 20 amino acids have the ability to elicit protection in mice. Fusions of 342 amino acids of Fujisawa SpaA and histidine hexamer (HisSpa1.0) protected pigs against challenge with both serotype 1 and serotype 2, the most important serotypes in the swine industry. Pigs immunized with HisSpa1.0 reacted well with both HisSpa1.0 and intact SpaA by enzyme-linked immunosorbent assay and immunoblotting. Serum collected at the time of challenge from a pig immunized with HisSpa1. 0 markedly enhanced the in vitro phagocytic and killing activity of pig neutrophils against the bacteria. DNA sequences of protective regions of spaA genes from five strains of serotypes 1 and 2 were almost identical. The full DNA sequences also seemed to be conserved among strains of all 12 serotype reference strains harboring the spaA gene by restriction fragment length polymorphism analysis of PCR products. These results indicates that SpaA is a common protective antigen of serotypes 1 and 2 of E. rhusiopathiae in swine and will be a useful tool for development of new types of vaccines and diagnostic tools for effective control of the disease.

Specific detection by flow cytometry of histidine-tagged ligands bound to their receptors using a tag-specific monoclonal antibody

Engineering proteins to contain a histidine (His)-tag has proved to be very useful for the purification and analyses of these molecules. In the present study, we demonstrate that the binding of His-tagged ligands to their receptors may be visualised by flow cytometry making use of a selected monoclonal antibody (mAb) against the His-tag. Employing this method, a recombinant C3a (rC3a) anaphylatoxin with a His-tag at its N-terminus could be shown to bind to C3a receptor (C3aR)-expressing RBL-2H3 transfectants with a half-maximal effective concentration (EC50) of about 3 nM which is well within the range of published affinity constants. Binding of a recombinant interleukin-8 (rIL-8) molecule with a C-terminal His-tag to RBL-2H3 cells which stably express the IL-8 receptors CXCR1 or CXCR2 could also be demonstrated using the tag-specific mAb. Furthermore, aminoterminally tagged C5a molecules of rat or human origin could be shown to bind to the human C5a receptor (C5aR). However, the fluorescence signal of the binding of rat rC5a to the human C5aR was distinctly higher over a wide range of ligand concentrations than the signal of human rC5a binding although both ligands were equally potent in the induction of chemotaxis in C5aR-expressing cells. Thus, the tag-specific mAb was able to interfere with the binding of human but not rat rC5a to the human C5aR. This observation is in agreement with the hypothesis of a two binding site model for the interaction of human C5a with its receptor whereas a different binding mode may apply for rat C5a. Our data demonstrate that the selected His-tag specific mAb may be a valuable tool for the visualisation of the binding of recombinant ligands to their receptors and may also provide useful information on the specific binding properties of the ligands.

[Heterologous expression of murine lymphotoxins in Escherichia coli and preparation of antibodies]

Genes encoding fragments of polypeptide chains of murine lymphotoxins (LT), namely, LT-alpha truncated from the N-terminus and the LT-beta extracellular domain, containing N-terminal hepta- and hexahistidine epitopes, respectively, were expressed in E. coli cells. The recombinant proteins purified by metallochelate chromatography were used to obtain polyclonal antibodies that specifically recognize murine LT.

Residue 3 of beta2-microglobulin affects binding of class I MHC molecules by the W6/32 antibody

Previous studies of class I MHC molecules have shown that the owl monkey (Aotus) possesses at least two variants of the beta2-microglobulin (beta2m) protein. These two variants have different isoelectric points, and exhibit differential reactivity with the monoclonal antibody W6/32. We report cDNA sequences of the B2m gene, from W6/32-positive and W6/32-negative Aotus cell lines. The two beta2m variants we identified exhibit a single amino acid difference at position three. An arginine residue at position 3 was correlated with W6/32 reactivity, whereas histidine was associated with non-reactivity. W6/32 reactivity was conferred to a W6/32-negative Aotus cell line when it was transfected with the B2m from the W6/32-positive cell line. Residue 3 of beta2m is located at the surface of the class I molecule. It is also close to position 121 of the MHC class I heavy chain, which has previously been shown to influence W6/32 antibody binding. We conclude that W6/32 binds a compact epitope on the class I molecule that includes both residue 3 of beta2m and residue 121 of the heavy chain. We examined the distribution of the two beta2m motifs in a sample Aotus population using an allele-specific polymerase chain reaction assay. The pattern of beta2m segregation we observed matches that which was defined previously by serology. Additionally, we identified laboratory-born hybrid animals who possess both variants of beta2m.

Activation of calpain in myocardial infarction: an immunohistochemical study using a calpain antibody raised against active site histidine-containing peptide

Tissue damage resulting from ischemia due to myocardial infarction is thought to be intensified by the proteolytic action of endogenous enzymes. Calpain (calcium dependent cysteine protease) is considered to be a highly likely candidate, since it is activated by calcium ion which increases in concentration under conditions of ischemia. We prepared a mono-specific antibody against the active site histidine stretch, Lys-Leu-Val-Lys-Gly-His-Ala-Tyr-Ser-Val, in the calpain 80 kDa large subunit. The specificity of the antibody was verified by its inhibitory effect on the caseinolytic activity of both mu- and m-calpains, western blotting analysis, and by absorption with the antigen peptide. The antibody was used to localize the intracellular distribution of activated calpains in infarcted regions of the human heart. The results showed that myocardial cells affected by ischemia were stained by the antibody, allowing damaged cells to be distinguished from cells of unaffected regions and that the immunostained regions were essentially the same regions as those identified by dense eosinophilic staining with hematoxylin and eosin. However, the staining pattern obtained with the antibody, was characteristic in denser staining at the cell periphery, whereas the damaged cells were stained homogeneously by hematoxylin and eosin. By the former method, results of staining indicated that the activation site of the calpain proenzyme was in the peri-plasma membrane, whereas by the latter method, diffusely distributed plasma proteins such as albumin and immunoglobulins were visualized as demonstrated in earlier reports.

Expression and rapid purification of an Aedes aegypti salivary allergen by a baculovirus system

Mosquito salivary proteins cause allergic reactions in humans. Recombinant salivary allergens will facilitate both the diagnosis and immunotherapy of mosquito allergy. The Aed a 1, a 68-kD apyrase in the saliva of Aedes aegypti, has been demonstrated to be an allergen which binds to the IgE of mosquito-allergic subjects. The baculovirus expression vector pBlueBacHis C equipped with an N-terminal histidine tag was used to express the Aed a 1 protein. The cDNA coding for the 3' significant portion of Aed a 1 (Aed a 1 3') (150-562 amino acid residues) was cloned into pBlueBacHis C. The rAed a 1 3' protein expressed by recombinant baculovirus was verified by immunoblot using anti-Aed a 1 and anti-histidine antibodies, respectively. The histidine-tagged fusion protein was purified to apparent homogeneity from infected Sf9 cells by Ni2+ resin affinity chromatography. Both immunoblot and ELISA showed that the purified rAed a 1 3' binds to the IgE and IgG in mosquito allergic sera, indicating that the antigenicity of the rAed a 1 3' is identical to the native Aed a 1 of Aedes aegypti saliva.

Heterologous expression of rat epitope-tagged histamine H2 receptors in insect Sf9 cells

1. Rat histamine H2 receptors were epitope-tagged with six histidine residues at the C-terminus to allow immunological detection of the receptor. Recombinant baculoviruses containing the epitope-tagged H2 receptor were prepared and were used to infect insect Sf9 cells. 2. The His-tagged H2 receptors expressed in insect Sf9 cells showed typical H2 receptor characteristics as determined with [125I]-aminopotentidine (APT) binding studies. 3. In Sf9 cells expressing the His-tagged H2 receptor histamine was able to stimulate cyclic AMP production 9 fold (EC50=2.1+/-0.1 microM) by use of the endogenous signalling pathway. The classical antagonists cimetidine, ranitidine and tiotidine inhibited histamine induced cyclic AMP production with Ki values of 0.60+/-0.43 microM, 0.25+/-0.15 microM and 28+/-7 nM, respectively (mean+/-s.e.mean, n=3). 4. The expression of the His-tagged H2 receptors in infected Sf9 cells reached functional levels of 6.6+/-0.6 pmol mg(-1) protein (mean+/-s.e.mean, n=3) after 3 days of infection. This represents about 2 x 10(6) copies of receptor/cell. Preincubation of the cells with 0.03 mM cholesterol-beta-cyclodextrin complex resulted in an increase of [125I]-APT binding up to 169+/-5% (mean+/-s.e.mean, n=3). 5. The addition of 0.03 mM cholesterol-beta-cyclodextrin complex did not affect histamine-induced cyclic AMP production. The EC50 value of histamine was 3.1+/-1.7 microM in the absence of cholesterol-beta-cyclodextrin complex and 11.1+/-5.5 microM in the presence of cholesterol-beta-cyclodextrin complex (mean+/-s.e.mean, n=3). Also, the amount of cyclic AMP produced in the presence of 100 microM histamine was identical, 85+/-18 pmol/10(6) cells in the absence and 81+/-11 pmol/10(6) cells in the presence of 0.03 mM cholesterol-beta-cyclodextrin complex (mean+/-s.e.mean, n=3). 6. Immunofluorescence studies with an antibody against the His-tag revealed that the majority of the His-tagged H2 receptors was localized inside the insect Sf9 cells, although plasma membrane labelling could be identified as well. 7. These experiments demonstrate the successful expression of His-tagged histamine H2 receptors in insect Sf9 cells. The H2 receptors couple functionally to the insect cell adenylate cyclase. However, our studies with cholesterol complementation and with immunofluorescent detection of the His-tag reveal that only a limited amount of H2 receptor protein is functional. These functional receptors are targeted to the plasma membrane.

Specific detection of his-tagged proteins with recombinant anti-His tag scFv-phosphatase or scFv-phage fusions

Using a cell-bound immunogen, we have generated a monoclonal antibody, 3D5, that recognizes carboxy-terminal oligo-histidine tags (His tags) on a wide variety of proteins. From this monoclonal antibody, we have generated a single-chain fragment of the variable domains (scFv), a dimeric scFv-alkaline phosphatase fusion and an oligovalent scFv-display phage. The antibody in its various formats is an effective tool used in fluorescence-activated cell sorting analysis, the BIAcore method, Western blots and enzyme-linked immunosorbent assay (ELISA). Western blots and ELISAs can be developed directly by using crude extracts of E.coli cells that produce the scFv-alkaline phosphatase fusion, thus providing an inexhaustable and convenient supply of detection reagent. Alternatively, oligovalent scFv-displaying phage can be used directly from culture supernatants for this purpose. The dissociation constants, KD of the peptide KGGHHHHH (KD = 4 x 10(-7) M) and of imidazole (KD = 4 x 10(-4) M) were determined. Molecular modeling of the Fv fragment suggests the occurrence of two salt bridges between the protonated histidine side chains of the peptide and the acidic groups in the antibody, explaining why the antibody or the substrate may be eluted under mildly basic conditions.

Rapid detection of the Fc gamma RIIA-H/R 131 ligand-binding polymorphism using an allele-specific restriction enzyme digestion (ASRED)

A polymorphism of the gene for Fc gamma RIIA, arginine (R) or histidine (H) at position 131, alters the ability of the receptor to bind certain IgG subclasses. Identification of the Fc gamma RIIA-H/R 131 genotype has assumed increasing importance in disorders of host defense, immunohematologic diseases and systemic autoimmune disorders. We report a new method for determination of this genotype in which an allele-specific restriction enzyme site is introduced into an Fc gamma RIIA PCR product from genomic DNA, and polymorphism assignment is determined by restriction enzyme digestion followed by agarose gel electrophoresis. This method is more rapid, more reliable and less expensive than currently available methods.

Determination of gizzerosine activity in fish meal with a homologous radioimmunoassay

A homologous RIA for the determination of toxic gizzerosine activity in commercial fish meals has been developed. Three polyclonal antibodies (GR316, GR415, and GR418) were produced in female rabbits and extensively characterized for their potential use in individual RIA. The RIA had lower detection limits of 0.048, 0.78, and 0.39 ng/mg using the three respective antibodies. Because gizzerosine is derived from lysine and histidine, crossreactivity with these amino acids, and with histamine was examined. The antibodies crossreacted with histamine from 21 to 100%. No crossreactivity with histidine or lysine was observed for any of the three antibodies. Antibody GR415 was chosen for determination of gizzerosine in extracted fish meal samples because crossreactivity of histamine using this antibody was only present at high concentrations, and the Ka value for gizzerosine was 10-fold greater than for histamine. A mild buffer extraction procedure was used, resulting in 98% gizzerosine recovery. Displacement curves from extracted and serially diluted fish meal samples were parallel with gizzerosine standard. Inter-and intra-assay coefficients of variation were 11 and 15%, respectively. We used the RIA for determination of gizzerosine activity in a pool of 23 fish meal samples of known gizzerosine scores (determined with a chick bioassay), and histamine content. The partial correlation coefficient between gizzerosine content determined by the RIA and gizzerosine scores from the bioassay was high (0.83), and significant (P < 0.01). There were also significant correlations between gizzerosine scores and histamine content of the fish meals (0.63, P < 0.01), and between histamine content and gizzerosine levels determined by the RIA (0.59, P < 0.01). The application of the homologous RIA for the determination of gizzerosine activity in commercial fish meals could be of importance for the prevention of gizzard erosions in the poultry industry, and for studying gizzerosine-induced pathology and metabolism.

Detection of histidine-tagged fusion proteins by using a high-specific mouse monoclonal anti-histidine tag antibody

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The monoclonal antibody specific for the 4-hydroxy-2-nonenal histidine adduct

Monoclonal antibodies directed against proteins modified with the major membrane lipid peroxidation product, 4-hydroxy-2-nonenal, have been established and characterized. The monoclonal antibodies specific for HNE-modified proteins were raised by immunizing mice with a HNE-keyhole limpet hemocyanin conjugate. The resulting five monoclonal antibodies (mAbs HNEJ-1-5) recognized HNE-modified bovine serum albumin (BSA), but not native BSA in Western blot studies. Of the five mAbs, HNEJ-2 exhibited the highest affinity for HNE-modified proteins and a much higher affinity for the HNE-histidine adduct than the HNE-lysine or HNE-cysteine adducts. mAb HNEJ-2 did not cross-react with proteins that had been treated with other aldehydes, such as 1-hexenal, 2-hexenal, 4-hydroxy-2-hexenal, 2-nonenal, formaldehyde, or glutaraldehyde. These results suggest that the major epitope recognized by mAb HNEJ-2 is the Michael addition-type HNE-histidine adduct.

Ultrastructural studies on peptides in the dorsal horn of the rat spinal cord--IV. Effects of peripheral axotomy with special reference to neuropeptide Y and vasoactive intestinal polypeptide/peptide histidine isoleucine

Using immunofluorescence histochemistry and pre- and post-embedding immunoelectron microscopy the rat lumbar dorsal horn was analysed in normal rats and 14 days after unilateral transection of the sciatic nerve. A marked increase in neuropeptide Y-like immunoreactivity was observed in the ipsilateral, superficial dorsal horn, especially in laminae III and IV, of the lumbar 4-5 spinal cord segments after peripheral axotomy. In the ipsilateral lamina II two types of neuropeptide Y-immunoreactive, presumably primary afferent terminals could be identified at the ultrastructural level. The first type contained many large dense-core vesicles (100-155 nm in diameter), whereas a second, more common type had only a few and smaller large dense-core vesicles (80-100 nm in diameter), plus synaptic vesicles of varying diameter (50-85 nm), large empty vesicles and tubular structures. Only occasionally were neuropeptide Y-positive terminals in lamina II involved in the formation of axonal labyrinths. In the ipsilateral lamina III, the number of neuropeptide Y-positive nerve terminals markedly increased after axotomy, with a moderate increase in lamina IV. These neuropeptide Y-positive terminals were morphologically similar to the second type of neuropeptide Y-positive terminal in lamina II, i.e. contained many synaptic vesicles (45-50 nm in diameter), a few small large dense-core vesicles (80-100 nm in diameter), electron-dense granular matrix and a few tubular structures. Fusion of synaptic vesicles with the plasma membrane was often observed at these synapses. These terminals frequently formed glomeruli but were not involved in axonal labyrinths. With regard to local neurons, neuropeptide Y-like immunoreactivity was observed in many dendrite-like profiles mostly making synaptic contacts with neuropeptide Y-negative dendrites and only rarely contacting the central terminal of the glomeruli. Neuropeptide Y-positive nerve endings were mainly seen in lamina I and the outer third of lamina II. After peripheral axotomy the number of vasoactive intestinal polypeptide/peptide histidine isoleucine immunoreactive terminals was increased in laminae I and II. They contained many large dense-core vesicles (100-120 nm in diameter), and some of them were positive for vasoactive intestinal polypeptide/peptide histidine isoleucine. Morphologically, the terminals were characterized by a granular matrix, tubular structures, empty vesicles, reduction in synaptic vesicles and absence of postsynaptic densities. Vasoactive intestinal polypeptide/peptide histidine isoleucine-like immunoreactivities were often found in association with labyrinth formation.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of histidine residue modification on the immune precipitating ability of rabbit IgG

Treatment of anti-ovalbumin rabbit IgG with diethylpyrocarbonate (DEPC) at concentrations up to 100 microM led to a progressive decrease in the rates of formation of insoluble immune complexes, without affecting the final extent of immune complex formation. DEPC concentrations approximately 10-fold higher were needed to give comparable decreases in the rates of immune complex formation by F(ab')2. Treatment of DEPC-treated IgG with hydroxylamine led to substantial restoration of the rates of formation of insoluble immune complexes. Carbethoxylation of two histidine residues per IgG molecule had little effect on rates of formation of insoluble immune complexes, but these rates were markedly decreased in samples of IgG with four to five histidines per molecule modified. There were parallel decreases in the protein A-binding activity and in the rates of formation of insoluble immune complexes in IgG treated with increasing concentrations of DEPC. The presence of complement protein C1q restored the rates of formation of insoluble immune complexes of DEPC-treated IgG.

Amino acid sequence of the region of beta 2-glycoprotein 1 (gp1) which mediates binding of autoantibodies to the cardiolipin-gp1 complex in humans

Anticardiolipin antibodies (ACA) in sera from patients with autoimmune and infectious diseases were tested for binding to beta 2-glycoprotein 1 (gp1) in order to determine whether human gp1 acts as a cofactor for the binding of ACA to cardiolipin (CL) or as an antigen recognized by ACA. While none of the ACA-positive sera tested recognized gp1 by itself, gp1 was necessary for the binding of ACA to CL in sera from four patients with autoimmune diseases. In three of the four sera the presence of lupus anticoagulant (LA) was detected by prolonged partial thromboplastin time (PTT). Examinations using the bovine equivalent of human gp1 contained in fetal calf serum (FCS) and adult bovine serum (ABS) showed that the human protein can be replaced by the bovine equivalent in the enzyme-linked immunosorbent assay (ELISA). Using affinity-purified antibodies directed against the CL-gp1 complex it was shown that the binding of these antibodies is dependent on the concentration of the bovine gp1 equivalent contained in the formed complex. Similar results found with the human gp1 confirmed this assertion. In order to find out which region of gp1 might mediate the binding between ACA and cardiolipin, we examined to what extent selected oligopeptide sequences of gp1 can substitute for the protein. Peptide P2 (representing the amino acids at positions 268-278 of the gp1 molecule) and gp1 showed about the same binding capacity. Histidine in this peptide seems to be essential for the binding to CL as we found decreased binding with peptides modified in this position. Conclusions from this work show that gp1 does not act as a relevant antigen for ACA, but occupies an essential function in the complex formed with cardiolipin for a certain group of ACA.

Production of bioactive rabbit antibodies against the mutated receptor peptide TSH-R-HIS17 and detection of hypertriiodothyroninemia in the rabbit

We produced rabbit antibodies against mutated thyrotropin (TSH) receptor peptide TSH-R-HIS17 in comparison with non-mutated TSH receptor peptide TSH-R-ASP17. All the antibodies raised against TSH-R-HIS17 showed thyroid stimulating antibody (TSAb), thyroid stimulation blocking antibody (TSBAb) and/or TSH binding inhibiting immunoglobulin (TBII) activities and also those serum T3 levels were all in thyrotoxic levels associated with TSAb activities. However, all the antibodies raised against TSH-R-ASP17 had no activities of TSAb, TSBAb and/or TBII and those serum T3 levels were all within normal range. The data suggest that the mutation in the TSH receptor gene may have a possible relevance for the pathogenesis of Graves' disease.

Involvement of the Zn-binding region of tetanus toxin in B and T recognition. Influence of Zn fixation

Tetanus toxin contains a metal-binding site for zinc, located in its light chain. The sequence accounting for Zn fixation is part of a predicted amphipathic helical secondary structure and corresponds to a putative T cell epitope according to Rothbard and Taylor (EMBO J. 7, 93-100, 1988). In this paper, we analyse the antigenic properties of two synthetic peptides (233-248 = P12 and 225-243 = P13) containing the Zn binding sequence. Our results show that peptide P13 contains a B and T epitope. The B epitope seems to be immuno-dominant whether the T epitope is at least DR2 restricted. Zn binding on P13 leads to a decrease in its recognition by both antibodies and T lymphocytes.

Characterization of a human protein threonine kinase isolated by screening an expression library with antibodies to phosphotyrosine

We have studied the activity and substrate specificity of the catalytic domain of a protein kinase that was isolated in a screen of a human lambda gt11 fibroblast cDNA library with anti-phosphotyrosine antibodies. The sequence of this protein kinase would predict that it is a protein serine/threonine kinase, which at first seemed incongruent with the cloning method. However, recent reports indicate that some protein kinases can phosphorylate both tyrosine and serine/threonine residues. To determine whether this protein kinase, which we call PYT (for phosphotyrosine picked threonine kinase), was a dual-specificity protein kinase we investigated its substrate specificity when expressed in bacteria. The catalytic domain was active as a protein kinase when expressed from any of several promoters and when expressed as a TrpE fusion protein. All experiments that resulted in an active protein kinase, as judged by incorporation of 32P by metabolic labeling, also resulted in the generation of proteins that were recognized by anti-phosphotyrosine antibodies. Phosphoamino acid analyses of the metabolically labeled proteins that were recognized by the antibodies consistently yielded large amounts of phosphothreonine and only trace amounts of phosphotyrosine. We mapped the phosphorylation sites in the phosphorylated PYT protein and found only phosphothreonine; 90% of the radioactivity mapped to a threonine in the region autophosphorylated by many protein kinases. These data demonstrate that PYT is primarily a protein threonine kinase, but that it can phosphorylate tyrosine to a small extent, making it a potential dual-specificity protein kinase.

Immunochemical reactivity of native and modified preparations of pig kidney diamine oxidase

This paper describes the antigenicity of pig kidney diamine oxidase [EC 1.4.3.6] and the possible role of constituent amino acids in the epitope structure of the enzyme. The loss of 62% of the biological activity after DAO-anti-DAO antibodies interaction was attributed to the steric hindrance caused by binding of antibody to the enzyme molecule. A gradual loss in antigenicity during ultraviolet (UV) irradiation was observed without any significant conformational change, demonstrating the destruction of antigenic determinants. However, ethoxyformylation of nine histidyl residues with complete inactivation caused no change in immunoreactivity. The results indicate that the antigenic sites and catalytic sites are located at different positions along the polypeptide chain. Moreover, the results of lysine residue modification were suggestive of possible involvement of lysine in the antigenic determinants of DAO.

Rh antigen immunoreactivity after histidine modification

125I-anti-D IgG and unlabeled blood group allo-antisera in combination with 125I-protein A were employed in assessing antibody binding to red cells (RBC) treated with histidine reagents. The acylating reagent diethylpyrocarbonate (DEP), the alkylating reagent p-bromophenacyl bromide (pBPB) and the photosensitizer dye Rose Bengal (RB) were used under conditions that usually result in the selective modification of histidine in isolated proteins. Progressive apparent inactivation of the D antigen in ghost membranes occurred with increasing DEP concns, which was not demonstrably reversible by hydroxylamine since this reagent itself inactivated the D antigen. Exposure of red cells to 5 mM p BPB resulted in a 50% decrease in binding of 125I-anti-D IgG. Photo-oxidation of RBC in the presence of Rose Bengal apparently inactivated all the major Rh antigens as detected either by labeled anti-D IgG binding, IgG agglutinating serological reagents, or the binding of 125I-labeled protein A following the sensitization of cells with unlabeled antisera. Under conditions of RB treatment, where hemolysis was absent or minimal, 125I anti-D IgG binding decreased to 38-49% of the level seen in controls. Rose Bengal treatment of R1r RBC revealed varying inactivation of all the Rh antigens, i.e. D 15%, C 89%, c 73%, e 54% inactivated, whereas antibody binding activity of the Fya and Fyb antigens present in the same cell was unaffected. Previous reports as well as the pH profile of anti-D binding have implicated the participation of histidine in Rh antigen expression. Our results are consistent with histidine involvement in Rh activity. Whether Rh antigens have essential histidine(s) involved directly in epitope structure, or instead depend on a critical histidine(s) at the lipid-protein interface that modulates antigen expression remains to be determined.