Immobilization of binding proteins on nonporous supports. Comparison of protein loading, activity, and stability

Four different nonporous particulate materials, nylon, polystyrene, soda-lime silicate glass, and fused silica glass, have been evaluated for their appropriateness as immobilization supports for immunoglobulins. A method of protein quantitation that is usually applied to solutions, the bicinchoninic acid (BCA) assay, was used successfully to directly measure ng amounts of protein immobilized on the supports. Two proteins, a monoclonal antibody to theophylline and the biotin binding protein avidin, were studied. Radioactive theophylline and radioactive biotin were used to measure the activity of the immobilized protein. Ligand binding capacity per mm2 of support was measured as a function of amount of protein immobilized. By measuring both the amount of protein immobilized and its ligand binding capacity, we have determined that antitheophylline antibody adsorbed on polystyrene balls loses almost 90% of its binding activity after 65 h, although little protein is lost from the balls over this time. Avidin retains nearly full activity for biotin on polystyrene. The binding activity of biotinyl-antibody conjugate immobilized on avidin-adsorbed polystyrene is stable, even when stored for over 22 wk. Antibody covalently immobilized on soda-lime silicate glass beads retains its binding activity over long-term storage, although only 0.1 mol of 3H-theophylline bind per mol of immobilized antibody. Using fused silica glass particles as the solid support, the same antibody binds approx 0.6 mol of ligand per mol of immobilized antibody protein. The structural "softness" of the immunoglobulin requires that interaction with the surface be prevented in order to maintain activity.

Light chain composition of serum granulocyte binding immunoglobulins

Serum granulocyte binding IgG, IgM, and the light chain composition of granulocyte binding immunoglobulins were measured in 58 adult subjects, including 8 normal individuals, 6 with Felty syndrome, 6 with chronic idiopathic neutropenia, 32 with B-cell chronic lymphocytic leukemia (CLL), and 6 with multiple myeloma. An abnormal kappa/lambda ratio of granulocyte binding immunoglobulins was detected in 12 of 32 patients with CLL. Neutropenia in patients with CLL did not correlate with an abnormal kappa/lambda ratio or excess granulocyte binding IgG, but did correlate with granulocyte binding IgM (P less than 0.02). Eight of the 12 patients (5 with chronic idiopathic neutropenia and 3 with Felty syndrome) with an immune neutropenia without underlying neoplastic disorder had light chain restricted granulocyte binding immunoglobulins. Of all patients' sera with light chain restriction, 76% were of lambda light chain isotype. Thus, the frequent detection of light chain restriction of granulocyte binding immunoglobulins is not a reflection of malignancy but is suggestive of the somatic mutation of immunoglobulin light chain genes.

Hybrid myeloma cells which secrete heterodimeric IgG: a model to study the N-linked glycan

Fundamental questions remain unanswered regarding the effect of the acceptor polypeptide structure on the fine structure of the N-linked glycan of glycoproteins and conversely, the effect of the glycan structure of IgG on the function and structure of the protein. The construction of myeloma hybrids capable of secreting multiple IgG which differ with regard to the fine structure of their N-linked oligosaccharides would be a valuable model for studying these questions. P3X63Ag8 analogous glycan of the IgG2b secreted by Sp2/HLBu. Fusion hybrids of these cells secrete parental IgG1, and to a lesser degree IgG2b, as well as a heterodimeric IgG containing both the gamma 1 and gamma 2b chains. The oligosaccharide of each chain is identical in structure to the appropriate parental IgG. Such cells allow for the analysis of acceptor properties that influence glycan fine structure, as well as the role of glycan structure on the stability of the IgG.

Structure of the chicken neuron-glia cell adhesion molecule, Ng-CAM: origin of the polypeptides and relation to the Ig superfamily

The neuron-glia cell adhesion molecule (Ng-CAM) mediates both neuron-neuron and neuron-glia adhesion; it is detected on SDS-PAGE as a predominant 135-kD glycoprotein, with minor components of 80, 190, and 210 kD. We have isolated cDNA clones encoding the entire sequence of chicken Ng-CAM. The predicted extracellular region includes six immunoglobulin-like domains followed by five fibronectin-type III repeats, structural features that are characteristic of several neural CAMs of the N-CAM superfamily. The amino acid sequence of chicken Ng-CAM is most similar to that of mouse L1 but the overall identity is only 40% and Ng-CAM contains a short fibronectin-like segment with an RGD sequence that has no counterpart in L1. These findings suggest that Ng-CAM and L1 may not be equivalent molecules in chicken and mouse. The amino-terminal sequences of the 210-, 190-, and 135-kD components of Ng-CAM are all the same as the predicted amino terminus of the molecule, whereas the 80-kD component begins within the third fibronectin repeat. The cDNA sequence is continuous across the junction between the 135- and 80-kD components, and a single 170-kD Ng-CAM polypeptide was isolated from tunicamycin-treated cells. In addition, all cDNA probes hybridized on Northern blots to a 6-kb RNA, and most hybridized to single bands on Southern blots. These results indicate that the Ng-CAM components are derived from a single polypeptide encoded by a single gene, and that the 135- and 80-kD components are generated from the 210/190-kD species by proteolytic cleavage. The 135-kD component contains most of the extracellular region including all of the immunoglobulin-like domains. It has no transmembrane segment, but it is tightly associated with the membrane. The 80-kD component contains two and a half type III repeats plus the RGD-containing segment, as well as the single transmembrane and cytoplasmic domains. These structural features of Ng-CAM provide a framework for understanding its multiple functions in neuron-neuron interactions, neurite fasciculation, and neuron-glia interactions.

Two vaccinia virus proteins structurally related to the interleukin-1 receptor and the immunoglobulin superfamily

The structures of two vaccinia virus genes (B15R and B18R) from near the right inverted terminal repeat are described. These genes encode proteins of 36.5K and 40.7K, respectively, which have an N-terminal hydrophobic sequence, possible sites for attachment of N-linked carbohydrate and a short string of hydrophobic residues near the C terminus. These properties are consistent with the mature proteins being either virion, cell surface or secretory glycoproteins. Protein sequence comparisons established that the two gene products are related to each other (20% identity) and to the immunoglobulin (Ig) superfamily. Intriguingly, the nearest homologues of these proteins in the SWISS-PROT (version 14) database are the human and murine interleukin-1 receptors, although both proteins are related to a wide range of Ig superfamily members, including the interleukin-6 receptor. The product of one of these genes is known to be expressed on the cell surface early during infection and immunity directed against it confer resistance to virus infection without directly neutralizing virus infectivity. We propose a novel method for virus immune evasion in which the product of one or both of these proteins may bind interleukin-1 and/or interleukin-6 and prevent these cytokines reaching their natural receptors. In consequence the inflammatory response would be diminished and virus replication enhanced.

Stability of European anti-D immunoglobulin preparations

The stability of 18 batches of anti-D immunoglobulin preparations from 7 European manufacturers was studied over 28-day incubation at +37 degrees C and 3-year storage at +4 degrees C. The mean loss of activity after 28 days at +37 degrees C was 12.3 +/- 8.2%, and after 3 years at +4 degrees C 15.2 +/- 9.5%. The correlation coefficient of the loss of activity between these two storages was r = 0.61, p less than 0.05 indicating that short-term incubation can be used to evaluate the shelf life stability of anti-D activity. In general, measurements of IgG fragments or activities of plasmin, plasminogen, or prekallikrein activator were not valuable in predicting the stability of anti-D activity due to the fact that the preparation of each manufacturer has its own unique pattern of enzymes and inhibitors. The anti-D immunoglobulin preparations contained up to at least 7 plasma proteins in addition to IgG. All preparations contained factor B, most of them alpha 2-macroglobulin, alpha 1-antitrypsin, albumin, and alpha 2-HS glycoprotein, alpha-Lysozyme was present in 7, and ceruloplasmin in 2 preparations. Neither purity nor impurity correlated with stability.

On the skew distribution of immunoglobulins and the inverted protein-folding problem

The question of antibody specificity is discussed in the framework of the inverted protein-folding problem (i.e. the characterization of protein sequences with a common fold). A stochastic model of the immune response, patterned after a model for the distribution of words in natural languages is proposed. It is shown that the steady-state probability distribution of immunoglobulin variable-region frequencies is the Yule distribution.

Size and structure of antigen-antibody complexes: thermodynamic parameters

The role of antigen-antibody (Ag-Ab) complexes in the immune response depends, in part, on the size of the complexes. Previously, we combined electron microscopy with classical and quasi-elastic light scattering to characterize the molecular weight distribution and the conformation of Ag-Ab complexes made from bovine serum albumin (BSA) and pairs of anti-BSA monoclonal antibodies at a single concentration and Ag:Ab molar ratio. In this report, the molecular weight distribution of Ag-Ab complexes was determined by classical light scattering at a single Ag:Ab ratio and over a range of concentrations, and binding of BSA to pairs of MAb was determined by radioimmunoassay at several Ag:Ab molar ratios. A thermodynamic model was developed for the equilibrium size distribution of Ag-Ab complexes formed between a pair of MAb, each with unique affinity and specificity, and an Ag containing a single epitope for each of the pair of MAb. The combined experimental data were used in conjunction with the model to determine the values of cyclization and polymerization constants. Successful determination of the parameters required data from both classical light scattering and electron microscopy. Cyclization constants were lower than those reported in other studies of Ag-Ab complexes; this may be attributable to our use of a protein Ag, as compared to a divalent hapten. In two out of three cases, cyclization constants increased with increasing number of Ab in the complex, in contrast to previous assumptions. The validity of the thermodynamic model was further shown by its ability, in combination with conformational and hydrodynamic model, to predict the hydrodynamic radius of the complexes over a wide range of experimental conditions.

Purification and characterization of IgG immunoconglutinins from patients with systemic lupus erythematosus: implications for a regulatory function

The levels of IgG immunoconglutinins in plasma from patients with rheumatoid arthritis, systemic lupus erythematosus and primary biliary cirrhosis were monitored by ELISA. High levels of IgG immunoconglutinins were found mainly in plasma from patients with systemic lupus erythematosus. These immunoconglutinins bound to microtitre plate-fixed C3, C3b and C3c but poorly to C3d. This binding was inhibited by particle-bound C3b and iC3b but not by the corresponding soluble fragments. Furthermore, Western blot analysis revealed no immunoconglutinin-binding to reduced C3 peptides and no binding was shown to soluble C3 alpha and beta chain by ELISA. IgG immunoconglutinins were purified from three plasma specimens by affinity chromatography on activated thiol sepharose ATS/C3 fragments. Two immunoconglutinin preparations that preferentially recognize ATS-C3b, inhibited C5-convertase function by 50-100% while one immunoconglutinin that recognized ATS-C3d,g had no effect. The two former immunoconglutinins also inhibited all three factor I cleavages in C3 alpha chain but the latter inhibited only the third cleavage. None of the immunoconglutinins affected the binding of complement-coated anti-BSA/BSA complexes to CR1 (CD35) on human erythrocytes, but the two immunoconglutinins that inhibited all factor I cleavages also inhibited the factor I-induced release of anti-BSA/BSA complexes from CR1. The results show that immunoconglutinins recognize specific epitopes on bound C3 fragments and that they are able to modulate C3-mediated functions.

Chemical modification of tryptophan residues and stability changes in proteins

The role of tryptophan residues in the stability of proteins was studied by ozone oxidation, which causes a small change in the tryptophan side chain. Trp 187 of the constant fragment of a type lambda immunoglobulin light chain, Trp 59 of ribonuclease T1, and Trp 62 of hen egg white lysozyme were oxidized specifically by ozone to N'-formylkynurenine or kynurenine. Judging from their circular dichroic and fluorescence spectra, these modified proteins were found to be the same as those of the respective intact proteins. However, even the slight modification of a single tryptophan residue produced a large decrease in the stability of these proteins to guanidine hydrochloride and heat. The smaller the extent of exposure of the tryptophan residue, the greater the effect of the modification on the stability. The formal kinetic mechanism of unfolding and refolding by guanidine hydrochloride of the CL fragment was not altered by tryptophan oxidation, but the rate constants for unfolding and refolding changed. The thermal unfolding transitions were analyzed to obtain the thermodynamic parameters. The enthalpy and entropy changes for the modified proteins were larger than the respective values for the intact proteins.

Efficient recognition of immunoglobulin domains from amino acid sequences using a neural network

A neural network was trained using back propagation to recognize immunoglobulin domains from amino acid sequences. The program was designed to identify proteins exhibiting such domains with minimal rates of false positives and false negatives. The National Biomedical Research Foundation NEW protein sequences database was scanned to evaluate the performance of the program in recognizing mouse immunoglobulin sequences. The program correctly recognized 55 out of 56 mouse immunoglobulin sequences, corresponding to a recognition efficiency of 98.2% with an overall false positive rate of 7.3%. These data demonstrate that neural network-based search programs are well suited to search for sequences characterized by only a few well-conserved subsequences.

Structural features of the McPC603 Fab fragment not defined in the X-ray structure

The proteolytic Fab fragment of the well characterized antibody McPC603 was compared to the recombinant Fab fragment, which was obtained in functional form from an Escherichia coli expression system [(1989) Methods Enzymol. 178, 497-515]. We found evidence that the proteolytic fragment is glycosylated at Asn H160 in the CH1 domain, where additional electron density had been observed in the crystal structure [J. Mol. Biol. 190, 593-604]. In addition, its heavy chain is about 30 amino acids longer than visible in the electron density and thus contains the complete hinge region. These structural differences between the recombinant Fab fragment, which had been designed exactly according to the defined electron density, and the proteolytic Fab fragment of McPC603 had no effect on the hapten binding properties of these antigen binding fragments. Yet, it may be important to be aware of these structural features of McPC603 in folding studies and some comparative analyses of antibody structures.

Protease nexin-1. Localization in the human brain suggests a protective role against extravasated serine proteases

Protease nexin-1 (PN-1) is a potent thrombin inhibitor that is identical to the glia-derived neurite-promoting factor or glia-derived nexin. Here we report immunocytochemical studies of adult human cerebral cortex that revealed the presence of strong immunoreactivity for PN-1 in capillaries and in the smooth muscle cells of arteries and arterioles. Expression of PN-1 was also abundant in astroglial processes in the parenchyma and in perivascular astroglial endfeet of human cerebral cortex. In situ hybridization with an 35S-labeled RNA antisense probe for PN-1 resulted in significant labeling of astrocytes and blood vessels. Because thrombin is known to cause retraction of neurites and modification of astrocytic morphology at low concentrations, PN-1 around blood vessels may play a major protective role against extravasation of thrombin and possibly other serine protease into the human brain.

Feedback inhibition of B cell differentiation by monomeric immunoglobulin

Polyspecific monomeric immunoglobulin (Ig) isolated from either a commercial source (pooled, > 2000 donors), or an autologous donor was capable of inhibiting both B cell proliferation, induced by T dependent mitogens or T cell factors and B cell differentiation, induced by similar stimuli. These effects appear to be directed at the B cell itself since inhibition of differentiation is detectable when monomeric Ig is added to cultures of B cell lines in the presence of B cell differentiation factor (BCDF). The inhibition of B cell differentiation does not appear to relate to inhibition of B cell proliferation, as no detectable change is seen in thymidine incorporation or cell number in these cultures. Furthermore, the effect of monomeric lg appears to relate to an early event in B cell differentiation, as there is no effect of IgSRK on spontaneously secreting B cell lines and maturation to cytoplasmic Ig containing cells is markedly impaired. Therefore, monomeric Ig secreted by B cells may serve as an immunoregulator of further Ig secretion.

Isolation and characterization of the immunoglobin of pike (Esox lucius L.)

The purification of the immunoglobul in from pike serum and its physicochemical characterization is presented. The immunoglobul in was prepared by means of gel filtration and ion exchange chromatography. Measurements in the analytical ultracentrifuge showed a sedimentation constant of 15.0 S. A molecular weight of 650.000 was calculated. The immunoglobulin was composed of heavy and light chains of molecular weights 60.000 and 22.500, respectively. It is likely that the immunoglobulin of pike is composed of 8 heavy and 8 light chains and possesses a tetrameric structure. The heavy chains contain 9.2% sugars and amino sugars. The amino acid composition of the chains is similar to that of other fish immunoglobulins.