Improved methods for prepurification and detection of staphylococcal enterotoxin B from cell-free culture filtrate

An improved ELISA method for the detection of Staphylococcal Enterotoxin B (SEB) in protein A preparations is presented. Fab fragments were obtained by digestion with papain of anti-SEB IgG bound to SEB immobilized on Sepharose 4B. Anti-SEB and peroxidase-labeled Fab fragments from secondary antibodies were successfully used in a modified ELISA of SEB in protein A preparations. SEB-Sepharose was used repeatedly for the production of anti-SEB Fab fragments by papain digestion without loss of affinity. In addition, for the purification of SEB from crude culture filtrates, an initial step utilizing a combined heat and pH treatment for the removal of significant amounts of contaminating proteins without losses of toxin activity is presented. This pretreatment step yielded positive effects in further downstream processing considering both shortened time and an increase in total recovery.     

Production of Fab fragments of monoclonal antibodies using polyelectrolyte complexes

A new method for the production of monovalent Fab fragments of antibodies has been developed. Traditionally Fab fragments are produced by proteolytic digestion of antibodies in solution followed by isolation of Fab fragments. In the case of monoclonal antibodies against inactivated subunits of glyceraldehyde-3-phosphate dehydrogenase, digestion with papain resulted in significant damage of the binding sites of the Fab fragments. Antigen was covalently attached to the polycation, poly(N-ethyl-4-vinylpyridinium bromide). Proteolysis of monoclonal antibodies in the presence of the antigen-polycation conjugate followed by (i) precipitation induced by addition of polyanion, poly(methacrylic) acid, and pH shift from 7.3 to 6.5 and (ii) elution at pH 3.0 resulted in 90% immunologically competent Fab fragments. Moreover, the papain concentration required for proteolysis was 10 times less in the case of antibodies bound to the antigen-polycation conjugate than that of free antibodies in solution. The digestion of antibodies bound to the antigen-polyelectrolyte complex was less damaging, suggesting that binding to the antigen-polycation conjugate not only protected binding sites of monoclonal antibodies from proteolytic damage but also facilitated the proteolysis probably by exposing antibody molecules in a way convenient for proteolytic attack by papain.     

Purification of endogenous digitalis-like factor(s) from cord blood of neonate by immunoaffinity chromatography.

We have previously shown that antidigoxin antibodies may neutralize partially purified endogenous digitalis like factor(s) present in newborn (umbilical cord) plasma. We here report on the preparation of an immunoaffinity chromatographic system (high affinity digoxin-binding antibodies (Fab fragments) bound covalently to Sepharose) for the purification of endogenous digitalis like factor(s). Neonate plasma extract loses all its biological digitalis-like activity (erythrocyte 86Rb uptake inhibition) after absorption on Sepharose coupled to Fab fragments but not after absorption on uncoupled Sepharose. Endogenous digitalis like factor(s) absorbed to Sepharose coupled to Fab fragments can be eluted by methanol. Subsequent HPLC separation indicate that at least two molecular species with digitalis-like properties are retained by antibodies bound to Sepharose and can be recovered with methanol.     

Enzymatic and immunochemical properties of lysozyme—Restriction of recognition of lysozyme antigenic determinants in pigs

Pigs immunized with lysozyme responded by producing only nonprecipitating antibody throughout the immunization period. Fig antilysozyme antibodies were found to be resistant to papain fragmentation, only 33% of the antibodies were fragmented with papain. From the binding of fluorescein labeled or ¹⁴C-labeled lysozyme to antilysozyme antibodies it was concluded that the antibodies elicited in pigs recognized only two antigenic determinants of lysozyme. These results were confirmed from the binding of Fab fragments to ¹⁴C-lysozyme. Fab fragments prepared from precipitating rabbit antilysozyme antibody bound ¹⁴C-lysozyme at a molar ratio of Fab/lysozyme = 3. Therefore nonprecipitating antibodies are the outcome of recognition of only two antigenic determinants on lysozyme and inability to form a lattice structure when antibody and antigen interact. This work emphasizes the limitations of using antibodies as a biological reagent for delineating the antigenic determinants on proteins.     

Vasoactive intestinal peptide hydrolysis by antibody light chains

This paper describes evidence for hydrolysis of a neuropeptide, vasoactive intestinal peptide (VIP), by light chains purified from the IgG of a human subject positive for VIP binding antibodies. Purified IgG was digested with papain, resultant fragment antigen binding (Fab) fragments were reduced with 2-mercaptoethanol and alkylated with iodoacetamide, and light chains were purified by chromatography on immobilized antibodies to light chains and immobilized antibodies to heavy chains. Non-immunoglobulin components were undetectable in the light chain preparation, judged by sodium dodecyl sulfate-electrophoresis and Western blotting with anti-heavy and anti-light chain antibodies. The light chains hydrolyzed VIP with specific activity 32-fold greater than that of Fab, the pH optimum for light chain-mediated VIP hydrolysis was 7.0-7.5, and the hydrolytic activity was saturable (Vmax, 0.19 pmol/min/microgram light chains; substrate concentration at Vmax/2,380 nM).     

Immobilization of glyceraldehyde-3-phosphate dehydrogenase by non-covalent binding to specific antibodies and Fab-fragments coupled to Sepharose]

Rabbit antibodies to rat skeletal muscle glyceraldehyde-3-phosphate dehydrogenase, as well as monovalent Fab fragments of these antibodies were coupled to CNBr-activated Sepharose 4B. Rat skeletal muscle glyceraldehyde-3-phosphate dehydrogenase was then immobilized on a matrix by non-covalent binding to specific antibodies. Immobilized enzyme retains approximately 90% catalytic activity of the soluble dehydrogenase; pH optimum of activity and the Km value observed are changed as compared to the enzyme in solution. Glyceraldehyde-3-phosphate dehydrogenase immobilized on specific antibodies is shown to undergo adenine nucleotide-induced dissociation into dimers. The immobilized dimeric form of the enzyme thus obtained is catalytically active and capable of reassociating with the dimers of apoglyceraldehyde-3-phosphate dehydrogenase added in solution to the suspension of Sepharose.     

Inhibition of pancreatic colipase by antibodies and Fab fragments. Selective effects of two fractions of antibodies on the functional sites of the cofactor

Rabbit antiserum was raised against porcine pancreatic colipase and Fab fragments were prepared by papain digestion of purified antibodies followed by purification on protein A-Sepharose. Fab fragments showed inactivation toward porcine colipase activity similar to that of antiserum and purified antibodies. From inactivation studies carried out by incubating porcine colipase and lipase with Fab fragments in the absence of lipid or in the presence of triolein and sodium deoxycholate, it could be concluded that polyclonal antiporcine colipase antibodies contain fractions that bind specifically to epitopes at or near the functional regions of the porcine cofactor. Studies with an enzyme-linked immunosorbent assay showed that cross-reactivity of horse or chicken colipase with antiporcine colipase antiserum was lower than that of the human or porcine protein. Results of immunoactivation kinetic studies performed with the same proteins, fully confirmed these observations. Partial cross-reactivity between porcine and chicken colipases allowed us to fractionate antibodies by immunoaffinity chromatography on immobilized chicken colipase. Fraction I contains antibodies absorbed on porcine colipase not accessible when the cofactor is bound to lipid. Antibodies of fraction II, nonadsorbed on chicken colipase, inactivate porcine colipase preincubated with triolein/deoxycholate. Lipase had a protective effect against inactivation. Antibodies of fraction II bind likely to epitopes close to the specific region of colipase interacting with lipase. Our conclusions are in good agreement with analysis of the sequence of porcine, equine and human colipases by calculating local hydrophilicity indices.     

Intramolecular mobility of human major histocompatibility complex protein. A spin-label study

Membranes of human splenocytes were hydrolyzed by papain and extracellular portions of class I and class II HLA antigen molecules were isolated by monoclonal antibodies fixed on Sepharose 4B. The isolated proteins were spin-labeled by TEMPO-dichlorotriazine and the values of rotational correlation times (tau) of labeled proteins were found using dependencies of ESR spectra parameters vs viscosity at constant temperature. The tau-values were equal to 8 ns for class I molecules and 14 ns for class II molecules. These values are 2-3 times lower than predicted for a rigid ellipsoid with mol wt. 50 kDa (about 20 ns). This fact suggests the existence of flexibility of HLA molecules which seems to be important for their biological activity. In this respect extracellular portions of HLA antigen molecules resemble flexible Fc fragments (tau = 12 ns) and differ from rigid Fab fragments (tau = 20 ns) of immunoglobulins G. The values of tau of spin-labeled proteins adsorbed from membrane hydrolysates on IgG-column was equal to 6.5 ns. The proteins adsorbed on lentil lectin column (after isolation of HLA proteins) have the tau-values equal to 9 ns.     

A micropreparation of fluorescein conjugates of immunoglobulin G and Fab from serum

Protein A-Sepharose CL-4B (PAS) was used to isolate rabbit immunoglobulin G from crude anti-herpes simplex virus-1 serum. Papain treatment of the PAS-bound immunoglobulin G released Fab fragments from the solid support, while Fc-containing fragments remained bound to PAS. PAS-immobilized immunoglobulin G was fluoresceinated by reaction with fluorescein isothiocyanate followed by papain cleavage to yield fluorescein-conjugated Fab fragments in solution. These fragments retained activity toward herpes simplex virus-1 infected Vero cells as evaluated by immunofluorescence. This novel procedure represents the fastest and simplest method for preparing Fab or fluoresceinated Fab fragments directly from any volume of immune serum.     

Synthesis and screening of a rationally designed combinatorial library of affinity ligands mimicking protein L from Peptostreptococcus magnus

Rational design and combinatorial chemistry were utilized to search for lead protein L (PpL) mimetics for application as affinity ligands for the purification of antibodies and small fragments, such as Fab and scFv, and as potential diagnostic or therapeutic agents. Inspection of the key structural features of the complex between PpL and human Fab prompted the de novo design and combinatorial synthesis of a 169-membered solid-phase ligand library, which was assessed for binding to human IgG and subsequent selectivity for the Fab fragment. Eight ligands were selected, chemically characterized and compared with a commercial PpL-adsorbent for binding pure immunoglobulin fractions. The most promising lead, ligand 8/7, when immobilized on an agarose support, behaved in a similar fashion to PpL in isolating Fab fragments from papain digests of human IgG to a final purity of 97%.     

抗人IgG Fc片段及Fab段单抗的鉴定及应用

本实验采用木瓜酶水解,SPA柱亲合层析等手段得到人IgGFc段及Fab段,以Sigma抗人IgGfFc段和抗人IgG Fab段单抗为标准品,鉴定了细胞库中抗人IgG系列的部分细胞株,得到特异性分泌抗人IgG Fc段和抗人IgG Fab段单抗的细胞各一株。 在上述实验基础上,用抗人IgG Fc及抗人IgG Fab单抗分别制备了Sepharose4B亲合层析柱,提纯了酶解人IgG Fc、Fab片段,经ELISA法鉴定,相互之间无交叉反应。同时用此方法制备了人抗HBe Fab片段,并将该片段进行了过氧化物酶标记,用来配制HBe ELISA诊断盒,证明其生物活性未受影响,而且消除了类风湿因子引起的HBe Ag假阳性现象。因抗HBe单抗来源困难,如采用HBe多抗制备ELISA试剂,本法将是提高质量的一个好方法。     

Two routes for production and purification of Fab fragments in biopharmaceutical discovery research: Papain digestion of mAb and transient expression in mammalian cells

Fab (fragment that having the antigen binding site) of a monoclonal antibody (mAb) is widely required in biopharmaceutical research and development. At Centocor, two routes of Fab production and purification were used to enable a variety of research and development efforts, particularly, crystallographic studies of antibody–antigen interactions. One route utilizes papain digestion of an intact monoclonal antibody for Fab fragment production. After digestion, separation of the Fab fragment from the Fc (fragment that crystallizes) and residual intact antibody was achieved using protein A affinity chromatography. In another route, His-tagged Fab fragments were obtained by transient expression of an appropriate construct in mammalian cells, and typical yields are 1–20 mg of Fab fragment per liter of cell culture. The His-tagged Fab fragments were first captured using immobilized metal affinity chromatography (IMAC). To provide high quality protein sample for crystallization, Fabs from either proteolytic digestion or from direct expression were further purified using size-exclusion chromatography (SEC) and/or ion-exchange chromatography (IEC). The purified Fab fragments were characterized by mass spectrometry, SDS–PAGE, dynamic light scattering, and circular dichroism. Crystallization experiments demonstrated that the Fab fragments are of high quality to produce diffraction quality crystals suitable for X-ray crystallographic analysis.     

Glycosylation in the Fc domain of IgG increases resistance to proteolytic cleavage by papain

IgG antibodies (Abs) and fragments of IgG Abs are becoming major biotherapeutics to treat an assortment of human diseases. Commonly prepared fragments of IgGs include Fc, Fab, and F(ab')2 fragments, all of which can be made using the sulfhydryl protease papain, although prolonged digestion times and/or excessive amounts of papain typically result in further cleavage of the Fc domain into smaller fragments. During our attempts to use papain to isolate Fc fragments from different IgG monoclonal Abs, it was observed that prior removal of Fc glycans resulted in a faster rate of papain-mediated degradation of the Fc domain. Subsequent time-course experiments comparing glycosylated and deglycosylated versions of IgG antibodies showed that the majority of molecules in a deglycosylated IgG sample were converted into Fab, Fc, and smaller Fc fragments in less than one hour, whereas the original glycosylated IgG required more than two hours to convert into a comparable amount of Fab and Fc fragments. Furthermore, whereas papain digestion converted almost all of a deglycosylated Fc fragment into smaller fragments of approximately 10 and approximately 12 kDa within 4 h, more than 40% of a glycosylated Fc fragment remained intact even after 24 h of digestion. These results indicate that the presence of CH(2) domain glycans in either IgGs or purified Fc fragments increases resistance to papain digestion. Increased sensitivity of non-glycosylated Fc domains to papain is consistent with the Fc domains lacking a defined structure, as exemplified by their inability to bind Fcgamma receptors, since misfolded proteins are often degraded by proteases because of increased accessibility of their proteolytic cleavage sites. Based on these observations it is possible to use papain sensitivity as a means of assessing proper Fc structure of IgG molecules.     

Boar sperm surface glycoproteins: Isolation,localization, and temporal expression during spermatogenesis

Boar sperm glycoprotein fractions were isolated by Lens culinaris hemagglutinin affinity chromatography of detergent-solubilized ejaculated spermatozoa, followed by preparative sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. In order to develop methods for further investigations of the sperm proteins, we proceeded with two of the isolated glycoproteins. Antibodies were raised in female rabbits against each of the two sperm glycoproteins. By a combination of immunosorbent chromatography, using the antibodies obtained, and preparative SDS polyacrylamide gel electrophoresis, highly purified sperm proteins were isolated. The sperm proteins were immobilized on Sepharose gel columns and specific immunoglobulin Fab fragments were enriched by affinity chromatography. The specificity of the Fab fragments was ascertained by immunoprecipitation analysis. The Fab fragments were used in indirect immunofluorescence analysis to localize the corresponding antigens on the surface of boar spermatozoa. Both antigens were exclusively confined to the postacrosomal region. Immunohistochemical staining of boar testis sections revealed that both antigens are expressed from the spermatid stage. This technique also revealed that one of the antigens congregated at the Golgi complex-acrosome region during spermatogenesis.     

Binding of a monoclonal antibody and its Fab fragment to supported phospholipid monolayers measured by total internal reflection fluorescence microscopy.

The association of an anti-dinitrophenyl monoclonal antibody and its Fab fragment with supported phospholipid monolayers composed of a mixture of dipalmitoylphosphatidylcholine and dinitrophenyl-conjugated dipalmitoylphosphatidylethanolamine has been characterized with total internal reflection fluorescence microscopy. The surface densities of bound antibodies were measured as a function of the antibody and Fab solution concentrations, and as a function of the solution concentration of dinitrophenylglycine. The apparent association constant of Fab fragments with surface-associated haptens was approximately 10-fold lower than the association constant for haptens in solution, and the apparent surface association constant for intact antibodies was only approximately 10-fold higher than the constant for Fab fragments. Data analysis with simple theoretical models indicated that, at most antibody surface densities, 50-90% of membrane-associated intact antibodies were attached to the surface by two antigen binding sites.     

Demonstration of neutralizing autoantibodies against IL-1 alpha in sera from patients with rheumatoid arthritis

We have recently reported the presence of IgG which has a potent inhibitory activity against IL-1 alpha in some sera from patients with rheumatoid arthritis. The mechanism of this inhibition by IgG against IL-1 alpha is now elucidated. IgG with IL-1 alpha-inhibitory activity inhibited the binding of 125I-IL-1 alpha to receptors on rheumatoid synovial cells. In addition, preincubation of synovial cells with the inhibitory IgG did not block the binding of 125I-IL-1 alpha to receptors, suggesting a direct interaction between IgG and IL-1 alpha. To examine which region of the IgG, namely Fab or Fc region, has the inhibitory activity, the IgG was digested with papain, and Fab and Fc fragments were purified. Fab fragments, but not Fc fragments, inhibited both IL-1 alpha-induced thymocyte-proliferation and the binding of 125I-IL-1 alpha to receptors. We further demonstrated that the inhibitory IgG which was bound to protein A Sepharose could bind a significant amount of 125I-IL-1 alpha, whereas only a negligible binding of the radiolabeled ligand was detected when IgG without the inhibitory activity was used as control. Moreover, the binding of 125I-IL-1 alpha to IgG with the inhibitory activity was clearly blocked by Fab fragments of IgG having the inhibitory activity. Finally, affinity-purified IgG over an IL-alpha affinity column showed approximately 100-fold more potent inhibitory activity on IL-1 alpha-induced thymocyte proliferation compared with untreated IgG. From these results, we conclude that IgG molecules with IL-1-alpha-inhibitory activity are neutralizing autoantibodies against IL-1 alpha.     

Immobilization of human intestinal mucosa enzymes on sepharose.

Digestive enzymes from human intestinal mucosa were solubilized by Triton X-100 and papain and covalently bound to eyanogen bromide-activated Sepharose 4-B gel. Triton X-100 solubilized most of the activities, and 39.1 to 63.5% were immobilized on the carrier. The other enzymes, still bound on the microvilli, were subsequently solubilized by papain but then the yield of immobilization reached only 11.0 to 17.6%. The enzyme-Sepharose gel was freeze-dried with a filler and stored without loss of activity. The rate of hydrolysis of di- and trisaccharides, dipeptides, and p-nitrophenylphosphate was measured by incubation on a small column containing less than 0.03 U of immobilized activities. The enzymatic multiplicity and catalytic properties of the intestinal mucosa enzymes were fully recovered on the carrier. This method is proposed for routine evaluation of the digestibility of dipeptides and synthetic disaccharides.     

Region-selective labeling of antibodies as determined by electrospray ionization-mass spectrometry (ESI-MS)

The electrospray ionization-mass spectrometry (ESI-MS) analysis of three sets of monoclonal antibody-acridinium-9-carboxamide conjugates is described. The conjugates (nine total) were enzymatically digested using papain and the resulting fragments [Fc heavy chain, Fab, or F(ab')(2)] were analyzed using liquid chromatography/ESI-MS. The average number of labels per fragment were calculated using Sigma nx%, where n is the number of acridinium molecules covalently bound to the fragment and x% is the percent relative area of the corresponding peaks in the mass spectrum. When these values were normalized against the molecular weight of their respective region, antibody-dependent labeling patterns were observed. For antibodies T (anti-L-T(4)) and F (anti-FITC), there was a preference for conjugation of the Fab region over the Fc region. For antibody B (anti-biotin), the trend was reversed.     

Improved Protein-A separation of VH3 Fab from Fc after Papain Digestion of Antibodies

Antibody-binding fragments (Fab) are generated from whole antibodies by treatment with papain and can be separated from the Fc component using Protein-A affinity chromatography. Commercial kits are available, which facilitate the production and purification of Fab fragments; however, the manufacturer fails to report that this method is inefficient for antibodies with V_H3 domains as a result of the intrinsic variable region affinity for Protein-A. A commercially available, modified Protein-A resin (MabSelect SuRe) has been engineered for greater stability. Here, we report that an additional consequence of the modified resin is the ability to purify V_H3 family Fab fragments, which cannot be separated effectively from other components of the papain digest by traditional Protein-A resin. This improvement of a commonly used procedure is of significance, as increasingly, therapeutic antibodies are being derived from human origin, where V_H3 is the most abundantly used variable region family.     

Precise epitope mapping of malaria parasite inhibitory antibodies by TROSY NMR cross-saturation

We have applied NMR cross-saturation with TROSY detection to the problem of precisely mapping conformational epitopes on complete protein antigen molecules. We have investigated complexes of the Fab fragments of two antibodies that have parasite inhibitory activity, bound to the important malaria vaccine candidate antigen, Plasmodium falciparum MSP1(19). The results indicate remarkable overlap between these epitopes for inhibitory antibodies, and will provide a basis for theoretical modeling of the antibody-antigen interface.