Enhanced activity of immobilized dimethylmaleic anhydride-protected poly- and monoclonal antibodies

Isolation of antigens and antibodies by affinity chromatography

Antibody-antigen binding constants are commonly strong enough for an effective affinity purification of antibodies (by immobilized antigens) or antigens (by immobilized antibodies) to work out a straightforward purification method. A drawback is that antibodies are large protein molecules and subject to denaturation under conditions required for the elution from the complex. Structures of antigens can vary but usually antigens are also equally subject to similar problems. The lability of the components can sometimes make the procedure sophisticated, but usually in all cases it is possible to find a satisfactory approach. In certain cases, specific interactions of the Fc part of antibodies are more facile to exploit for their purification.

Oriented immobilization of biologically active proteins as a tool for revealing protein interactions and function

The advantages of oriented immobilization of biologically active proteins are good steric accessibilities of active binding sites and increased stability. This not only may help to increase the production of preparative procedures but is likely to promote current knowledge about how the living cells or tissues operate. Protein inactivation starts with the unfolding of the protein molecule by the contact of water with hydrophobic clusters located on the surface of protein molecules, which results in ice-like water structure. Reduction of the nonpolar surface area by the formation of a suitable biospecifc complex or by use of carbohydrate moieties thus may stabilize proteins. This review discusses oriented immobilization of antibodies by use of immobilized protein A or G. The section about oriented immobilization of proteins by use of their suitable antibodies covers immobilization of enzymes utilizing their adsorption on suitable immunosorbents prepared using monoclonal or polyclonal antibodies, preparation of bioaffinity adsorbent for the isolation of concanavalin A and immobilization of antibodies by use of antimouse immunoglobulin G, Fc-specific (i.e. specific towards the constant region of the molecule). In the further section immobilization of antibodies and enzymes through their carbohydrate moieties is described. Oriented immobilization of proteins can be also based on the use of boronate affinity gel or immobilized metal ion affinity chromatography technique. Biotin-avidin or streptavidin techniques are mostly used methods for oriented immobilization. Site-specific attachment of proteins to the surface of solid supports can be also achieved by enzyme, e.g., subtilisin, after introduction a single cysteine residue by site-directed mutagenesis.

Dot-blot analysis of the degree of covalent modification of proteins and antibodies at amino groups

The present study describes a rapid and sensitive dot-blot assay approach for determining the degree of covalent modification of amino groups in proteins. N-hydroxy-succinimide ester of acetic acid was used for irreversible, covalent modification of proteins whose reactive primary amino groups were reversibly blocked (or protected) with 2,3-dimethyl-maleic anhydride prior to processing. Immobilon AV affinity membrane was utilized for differential covalent attachment of the proteins to the activated ester on the membrane matrix, primarily through their protected epsilon-amino group of lysins. The efficacy of the method was demonstrated for a murine monoclonal antibody and for two human plasma proteins. The degree of covalent modification of proteins at their amino groups as estimated by the proposed method is compared with that obtained by using the conventional trinitrobenzene sulfonic acid (TNBS) method. Several advantages of the present method over the TNBS method are emphasized. The new method, which requires only nanograms of protein, is shown to be more sensitive than the TNBS method where the limit of detection is in the milligram range. The proposed assay is very specific and facile, and the advantage of small sample size requirement (1 microliter) provides sequential detection of multiple samples facilitating much higher precision in data obtained than that of the TNBS assay.

Effect of antibody orientation on immunosorbent performance

The impact of antibody orientation on immunosorbent efficiency was quantitatively assessed. A pH-dependent murine monoclonal antibody (Mab) against human protein C (hPC), recombinant hPC (rhPC) and two different immobilization chemistries and matrices were used as model systems. The lysyl groups of the rhPC were covalently modified with an acetic acid ester of N-hydroxysuccinimide and this modified rhPC was used as a Fab masking agent (FMA). The FMA was used to mask the antigen binding regions (Fab) of the Mab prior to and during covalent immobilization. Thereafter, the residual active sites of the support were inactivated and the FMA was removed. Mab was immobilizeed at low bead-averaged densities of about 0.4-1.1 mg Mab/mL matrix to minimize local density effects. Immunosorbents made using masked Mab (oriented coupling) gave antigen binding efficiencies (nAg) of 42-48% compared with 18-22% for those made by random coupling. The amount of (Fab)2 released from pepsin digestion of immunosorbents was about 3-4-fold higher for matrices having been made with FMA-masked Mab relative to unmasked Mab. Thus, the (Fab)2 accessibility to pepsin correlates well with higher functional efficiency (nAg) and serves as a measure of orientation. In summary, at low Mab density and a 2:1 molar rhPC to Mab binding stoichiometry, about 80% or more of the Mab randomly coupled through amino moieties was improperly oriented relative to oriented coupled Mab, which correlated with about 50% of lost Mab functionality upon immobilization.

Factors affecting the specific activity of immobilized antibodies and their biologically active fragments

Factors affecting the specific activity of immobilized antibodies and their biologically active fragments were studied with goat anti-mouse and goat anti-human immunoglobulin G. Antibodies were immobilized on HW 65 polymeric support matrix activated with carbonyldiimidazole, hydrazide and iodoacetic acid. The most significant factors influencing the specific activity of stochastic coupling of antibodies are multi-site attachment, multiple orientations and steric hindrance imposed by crowding of antibody and the size of the antigen. In oriented immobilization the specific activity is affected only by steric hindrance. The specific activity of immunosorbents prepared by immobilization of F(ab') fragments can be improved to almost 100% by limiting the amount of protein immobilization and the size of the antigen. The present study shows the protocols for optimizing immobilized antibody performance.

Eupergit C as a carrier for high-performance liquid chromatographic-based immunopurification of antigens and antibodies

An immunoaffinity purification system using C30N and C1Z Eupergit C beads was developed and optimized. Poly- and monoclonal antibodies were purified using immobilized antigens and antigens were purified using immobilized antibodies. Antigens were used that possess enzymic activities and the efficiency of antigen binding was determined from the enzymic activity of the matrix-bound immunocomplexes. High-performance immunoaffinity purification using Eupergit C beads proved to be highly specific, reproducible, free from protein leakage and possessed a low degree of non-specific adsorption of tissue proteins. These characteristics of the system were illustrated by the isolation of immunoglobulin G from serum and of human decidua proteins from the decidua tissue and from seminal plasma. These proteins were obtained at high purity in a single purification step, as shown by sodium dodecyl sulphate-polyacrylamide gel electrophoresis.

Identification, immunoaffinity purification and initial characterization of a novel 71 kD human decidua associated protein by use of specific monoclonal antibodies

This study is part of an ongoing attempt to identify and characterize proteins associated with the human decidual tissue. A novel decidual-associated glycoprotein with an apparent molecular weight of 71 kD named hDP71 (human decidual-protein 71), has been identified and purified by immunoaffinity technique using monoclonal antibodies. The monoclonal antibodies recognizing the hDP71 were raised against a partly purified preparation of decidual associated proteins, which was obtained by immunoabsorption of serum proteins from crude decidual extract. Although the hDP71 was copurified with another decidual-associated glycoprotein, the previously described hDP200 (Halperin et al., 1989), evidence is presented showing that the monoclonal antibodies described above are specific for hDP71.