Complex between Peptostreptococcus magnus protein L and a human antibody reveals structural convergence in the interaction modes of Fab binding proteins

BACKGROUND: Peptostreptococcus magnus protein L (PpL) is a multidomain, bacterial surface protein whose presence correlates with virulence. It consists of up to five homologous immunoglobulin binding domains that interact with the variable (VL) regions of kappa light chains found on two thirds of mammalian antibodies. RESULTS: We refined the crystal structure of the complex between a human antibody Fab fragment (2A2) and a single PpL domain (61 residues) to 2.7 A. The asymmetric unit contains two Fab molecules sandwiching a single PpL domain, which contacts similar VL framework regions of two light chains via independent interfaces. The residues contacted on VL are remote from the hypervariable loops. One PpL-Vkappa interface agrees with previous biochemical data, while the second is novel. Site-directed mutagenesis and analytical-centrifugation studies suggest that the two PpL binding sites have markedly different affinities for VL. The PpL residues in both interactions are well conserved among different Peptostreptococcus magnus strains. The Fab contact positions identified in the complex explain the high specificity of PpL for antibodies with kappa rather than lambda chains. CONCLUSIONS: The PpL-Fab complex shows the first interaction of a bacterial virulence factor with a Fab light chain outside the conventional combining site. Structural comparison with two other bacterial proteins interacting with the Fab heavy chain shows that PpL, structurally homologous to streptococcal SpG domains, shares with the latter a similar binding mode. These two bacterial surface proteins interact with their respective immunoglobulin regions through a similar beta zipper interaction.     

Alternate arrangement of PpL B3 domain and SpA D domain creates synergistic double-site binding to VH3 and Vkappa regions of fab

In our previous study, a kind of novel hybrid immunoglobulin (Ig)-binding proteins (IBPs) was obtained with the characteristic structure of alternately arranged Finegoldia magna (formerly Peptostreptococcus magnus) protein L (P. magnus protein L, PpL) B3 domain (B3) and Staphylococcal protein A (SpA) D domain (D). In this study, two representative molecules of these novel proteins, LD3 (B3-D-B3) and LD5 (B3-D-B3-D-B3) (LD3/5), showed substantially higher affinity for IgG-F(ab')2, IgM, and IgA than 4L (B3-B3-B3-B3) or SpA, which were also demonstrated by surface plasmon resonance detection. Further, LD5 showed much stronger binding to single-chain Fv (scFv) KM38 (V(H)3-V(kappa)I) than to KM41 (V(H)1-V(kappa)III) or KM36 (V(H)3-V(kappa)III). Competitive inhibition studies showed that 4L alone or in combination with SpA (4L + SpA) was a weaker inhibitor than LD3/5 in inhibiting LD3/5's binding to IgG-F(ab')2, IgM, or IgA. The computer modeling suggested that the B3-D arrangement in LD3/5 could simultaneously bind to V(H)3 and V(kappa). Thus, our results indicated for the first time that alternate arrangement of B3 and D domains creates synergistic double-site binding to V(H)3 and V(kappa) regions of fragment of antigen binding. The different competitive inhibition pattern of binding of LD5 to scFv KM38 by 4L + SpA suggested strict use of antibody conformation for this simultaneous double-site binding. The demonstration of this novel binding property would promote to achieve the designed hybrid IBPs for useful immunological applications.     

A method to confer Protein L binding ability to any antibody fragment

Recombinant antibody single-chain variable fragments (scFv) are difficult to purify homogeneously from a protein complex mixture. The most effective, specific and fastest method of purification is an affinity chromatography on Protein L (PpL) matrix. This protein is a multi-domain bacterial surface protein that is able to interact with conformational patterns on kappa light chains. It mainly recognizes amino acid residues located at the VL FR1 and some residues in the variable and constant (C_L) domain. Not all kappa chains are recognized, however, and the lack of C_L can reduce the interaction. From a scFv composed of IGKV10-94 according to IMGT®, it is possible, with several mutations, to transfer the motif from the IGKV12-46 naturally recognized by the PpL, and, with the single mutation T8P, to confer PpL recognition with a higher affinity. A second mutation S24R greatly improves the affinity, in particular by modifying the dissociation rate (k_d). The equilibrium dissociation constant (K_D) was measured at 7.2 10^-11 M by surface plasmon resonance. It was possible to confer PpL recognition to all kappa chains. This protein interaction can be modulated according to the characteristics of scFv (e.g., stability) and their use with conjugated PpL. This work could be extrapolated to recombinant monoclonal antibodies, and offers an alternative for protein A purification and detection.     

Recombinant production of a VL single domain antibody in Escherichia coli and analysis of its interaction with peptostreptococcal protein L

A kappa-light chain from a Fab expression system was truncated by the insertion of a stop codon in the gene sequence to produce a variable light (VL) single domain antibody (dAb). Here, we describe the expression of dAb in the periplasm of Escherichia coli through fermentation in a defined media. Immunoglobulin binding domains from peptostreptococcal protein L (PpL) have been shown to bind specifically to kappa-light chains. We have produced recombinant PpL, at high yield, and this was used to custom-produce PpL-Sepharose affinity columns. Here, we show that the affinity purification of VL dAb by this method is simple and efficient with no apparent loss in protein at any stage. The truncated dAb protein product was confirmed by electrospray mass spectrometry and N-terminal sequencing. When analyzed by SDS-PAGE it was shown to be over 95% pure and produced at yields of 35-65 mg/L of culture medium. The dAb protein produced was shown by NMR and CD to be a folded beta-sheet domain. This domain is bound by PpL with a Kd of approximately 50 nM as determined by stopped-flow fluorimetry.     

In vivo VL-targeted activation-induced apoptotic supraclonal deletion by a microbial B cell toxin

To interfere with host immune responses, some microbial pathogens produce proteins with the properties of superantigens, which can interact via conserved V region framework subdomains of the Ag receptors of lymphocytes rather than the complementarity-determining region involved in the binding of conventional Ags. In recent studies, we have elucidated how a model B cell superantigen affects the host immune system by targeting a conserved V(H) site on the Ag receptors of B lymphocytes. To determine whether these findings represent a general paradigm, we investigated the in vivo immunobiologic properties of protein L of Peptostreptococcus magnus (PpL), a microbial Ig-binding protein specific for a V region site on Ig L chains. Our studies confirmed that PpL binding is restricted to a subset of murine Vkappa-expressing B cells, and found that B cells with stronger PpL-binding activity are associated with certain B cell subsets: splenic marginal zone (CD21(high) CD23(low)), splenic CD1(+), peritoneal B-1a (IgD(low) CD5(+)), and CD21(high) CD24(high) B cells in peripheral lymph nodes, mesenteric lymph nodes, and Peyer's patches. Infusion of PpL triggered a sequence of events in B cell receptor (BCR)-targeted B cells, with rapid down-regulation of BCR, the induction of an activation phenotype, and limited rounds of proliferation. Apoptosis followed through a process heralded by the dissipation of mitochondrial membrane potential, the induction of the caspase pathway, DNA fragmentation, and the deposition of B cell apoptotic bodies. These studies define a common pathway by which microbial toxins that target V region-associated BCR sites induce programmed cell death.     

Immunoglobulin superantigen protein L induces IL-4 and IL-13 secretion from human Fc epsilon RI+ cells through interaction with the kappa light chains of IgE

Peptostreptococcus magnus protein L is a multidomain bacterial surface protein that correlates with virulence. It consists of up to five homologous Ig-binding domains (B1-B5) that interact with the variable domain of Ig kappa L chains. Intact protein L stimulates the synthesis and the release of IL-4 and IL-13 from human basophils in vitro. A protein L fragment covering the Ig-binding domains B1-B4 also induced IL-4 and IL-13 release from basophils. There was an excellent correlation (r(s) = 0.82; p < 0.001) between the maximal percent IL-4 release induced by protein L and that induced by anti-IgE and between intact protein L and the B1-B4 fragment (r(s) = 0.90; p < 0.01). Removal of IgE bound to basophils markedly reduced the IL-4 release induced by anti-IgE, protein L, and B1-B4. Preincubation of basophils with protein L or anti-IgE caused complete cross-desensitization to subsequent challenge with the heterologous stimulus. IgE purified from myeloma patients PS and PP (lambda chains) blocked anti-IgE-induced IL-4 release, but not the releasing activity of protein L. In contrast, IgE purified from myeloma patient ADZ (kappa chains) blocked both anti-IgE- and protein L-induced secretion. Cyclosporin A, but not cyclosporin H, inhibited protein L-induced release of IL-4 and IL-13 from basophils. Thus, protein L acts as a bacterial Ig superantigen to induce the synthesis and release of IL-4 and IL-13 from basophils by interacting with kappa L chains of the IgE isotype.     

抗A型肉毒毒素人源三结构域抗体的重组设计与表达

以获得的抗A型肉毒毒素人源单链抗体ScFvB17为模板 ,PCR扩增抗体ScFv基因的重链可变区 (VH)和轻链可变区 (Vκ) ,以重链恒定区 1(CH1) 5′端 12个氨基酸的序列作为连接肽 ,构建成三结构域抗体分子 :VH_连接肽_Vκ(VH Vκ)。重组VH Vκ抗体分子在大肠杆菌中得到高效表达 ,其表达量占菌体总蛋白质的 34%以上。表达的蛋白质在菌内形成包含体 ,采用镍柱金属鏊合层析法对该包含体进行纯化 ,得到了纯度高达 95 %的VH Vκ。ELISA等实验结果显示 ,重组设计并制备的三结构域抗体蛋白VH Vκ不但可以特异识别毒素抗原 ,具有与原母本单链抗体ScFv相同的抗原特异性 ,而且具有了更高的相对亲和力和稳定性。     

Evidence for plasticity and structural mimicry at the immunoglobulin light chain-protein L interface

The multidomain bacterial surface protein L (PpL) is a virulence factor expressed by only 10% of Peptostreptococcus magnus strains, and its expression is correlated with bacterial vaginosis. The molecular basis for its ability to recognize 60% of mammalian immunoglobulin light chain variable regions (V(L)) has been described recently by x-ray crystallography, which suggested the presence of two V(L) binding sites on each protein L domain (Graille, M., Stura, E. A., Housden, N. G., Beckingham, J. A., Bottomley, S. P., Beale, D., Taussig, M. J., Sutton, B. J., Gore, M. G., and Charbonnier, J. (2001) Structure 9, 679-687). Here, we report the crystal structure at 2.1 A resolution of a protein L mutant complexed to an Fab' fragment with only 50% of the V(L) residues interacting with PpL site 1 conserved. Comparison of the site 1 interface from both structures shows how protein L is able to accommodate these sequence differences and therefore bind to a large repertoire of Ig. The x-ray structure and NMR results confirm the existence of two V(L) binding sites on a single protein L domain. These sites exhibit a remarkable structural mimicry of growth factors binding to their receptors. This could explain the protein L superantigenic activity on human B lymphocytes.     

Efficient amplification and direct sequencing of mouse variable regions from any immunoglobulin gene family.

We have designed two original sets of oligonucleotide primers hybridizing the relatively conserved motifs within the immunoglobulin signal sequences of each of the 15 heavy chain and 18 kappa light chain gene families. Comparison of these 5' primers with the immunoglobulin signal sequences referenced in the Kabat database suggests that these oligonucleotide primers should hybridize with 89.4% of the 428 mouse heavy chain signal sequences and with 91.8% of the 320 kappa light chain signal sequences with no mismatch. Following PCR amplification using the designed primers and direct sequencing of the amplified products, we obtained full-length variable sequences belonging to major (V(H)1, V(H)2, V(H)3, Vkappa1 and Vkappa21) but also small-sized (V(H)9, V(H)14, Vkappa2, Vkappa9A/9B, Vkappa12/13, Vkappa23 and Vkappa33/34) gene families, from nine murine monoclonal antibodies. This strategy could be a powerful tool for antibody sequence assessment whatever the V gene family before humanization of mouse monoclonal antibody or identification of paratope-derived peptides.     

Protein L from Peptostreptococcus magnus binds to the kappa light chain variable domain.

Protein L is an immunoglobulin light chain-binding protein expressed by some strains of the anaerobic bacterial species Peptostreptococcus magnus. The major variable region subgroups of human kappa and lambda light chains were tested for protein L binding; V kappa I, V kappa III, and V kappa IV bound protein L, whereas no binding occurred with proteins of the V kappa II subgroup or with any lambda light chain subgroups. Studies of the protein L binding capacity of naturally occurring VL fragments, and VL- and CL-related trypsin- and pepsin-derived peptides prepared from a kappa I light chain, localized the site of interaction to the VL domain. The affinity constant for the binding to an isolated V kappa I fragment was comparable to that for the native protein (Ka 0.9 x 10(9) M-1 and Ka 1.5 x 10(9) M-1, respectively). No binding occurred with CL-related fragments. Extensive reduction and alkylation of the V kappa fragment or the native kappa chain resulted in complete loss of protein L binding. Although it is possible, from comparative amino acid sequence data, to identify certain VL-framework region residues that account for the selective binding of protein L by kappa I, kappa III, and kappa IV proteins, our studies indicate that this interaction is essentially dependent upon the tertiary structural integrity of the kappa chain VL domain.     

Protein LG: a hybrid molecule with unique immunoglobulin binding properties.

Immunoglobulin (Ig)-binding bacterial proteins have attracted theoretical interest for their role in molecular host-parasite interactions, and they are widely used as tools in immunology, biochemistry, medicine, and biotechnology. Protein L of the anaerobic bacterial species Peptostreptococcus magnus binds Ig light chains, whereas streptococcal protein G has affinity for the constant (Fc) region of IgG. In this report, Ig binding parts of protein L and protein G were combined to form a hybrid molecule, protein LG, which was found to bind a large majority of intact human Igs as well as Fc and Fab fragments, and Ig light chains. Binding to Ig was specific, and the affinity constants of the reactions between protein LG and human IgG, IgGFc fragments, and kappa light chains, determined by Scatchard plots, were 5.9 x 10(9), 2.2 x 10(9), and 2.0 x 10(9) M-1, respectively. The binding properties of protein LG were more complete as compared with previously described Ig-binding proteins when also tested against mouse and rat Igs. This hybrid protein thus represents a powerful tool for the binding, detection, and purification of antibodies and antibody fragments.     

Phage display and peptide mapping of an immunoglobulin light chain fibril-related conformational epitope

Amyloid fibrils and partially unfolded intermediates can be distinguished serologically from native amyloidogenic precursor proteins or peptides. In this regard, we previously had reported that mAb 11-1F4, generated by immunizing mice with a thermally denatured variable domain (VL) fragment of the human kappa4 Bence Jones protein Len, bound to a non-native conformational epitope located within the N-terminal 18 residues of fibrillar, as well as partially denatured, Ig light chains (O'Nuallain, B., et al. (2006) Biochemistry 46, 1240-1247). To define further the antibody binding site, we used random peptide phage display and epitope mapping of VL Len using wild-type and alanine-mutated Len peptides where it was shown that the antibody epitope was reliant on up to 10 of the first 15 residues of protein Len. Comparison of Vkappa and Vlambda N-terminal germline consensus sequences with protein Len and 11-1F4-binding phages indicated that this antibody's cross-reactivity with light chains was related to an invariant proline at position(s) 7 and/or 8, bulky hydrophobic residues at positions 11 and 13, and additionally, to the ability to accommodate amino acid diversity at positions 1-4. Sequence alignments of the phage peptides revealed a central proline, often flanked by aromatic residues. Taken together, these results have provided evidence for the structural basis of the specificity of 11-1F4 for both kappa and lambda light chain fibrils. We posit that the associated binding site involves a rare type VI beta-turn or touch-turn that is anchored by a cis-proline residue. The identification of an 11-1F4-related mimotope should facilitate development of pan-light chain fibril-reactive antibodies that could be used in the diagnosis and treatment of patients with AL amyloidosis.     

AID Activity in B Cells Strongly Correlates with Polyclonal Antibody Affinity Maturation in-vivo Following Pandemic 2009-H1N1 Vaccination in Humans

The role of Activation-Induced Cytidine Deaminase (AID) in somatic hypermutation and polyclonal antibody affinity maturation has not been shown for polyclonal responses in humans. We investigated whether AID induction in human B cells following H1N1pdm09 vaccination correlated with in-vivo antibody affinity maturation against hemagglutinin domains in plasma of young and elderly individuals. AID was measured by qPCR in B cells from individuals of different ages immunized with the H1N1pdm09 influenza vaccine. Polyclonal antibody affinity in human plasma for the HA1 and HA2 domains of the H1N1pdm09 hemagglutinin was measured by antibody-antigen complex dissociation rates using real time kinetics in Surface Plasmon Resonance. Results show an age-related decrease in AID induction in B cells following H1N1pdm09 vaccination. Levels of AID mRNA before vaccination and fold-increase of AID mRNA expression after H1N1pdm09 vaccination directly correlated with increase in polyclonal antibody affinity to the HA1 globular domain (but not to the conserved HA2 stalk). In the younger population, significant affinity maturation to the HA1 globular domain was observed, which associated with initial levels of AID and fold-increase in AID after vaccination. In some older individuals (>65 yr), higher affinity to the HA1 domain was observed before vaccination and H1N1pdm09 vaccination resulted in minimal change in antibody affinity, which correlated with low AID induction in this age group. These findings demonstrate for the first time a strong correlation between AID induction and in-vivo antibody affinity maturation in humans. The ability to generate high affinity antibodies could have significant impact on the elucidation of age-specific antibody responses following vaccination and eventual clinical efficacy and disease outcome.     

Crystal Structure of a Mucus-binding Protein Repeat Reveals an Unexpected Functional Immunoglobulin Binding Activity

Lactobacillus reuteri mucus-binding protein (MUB) is a cell-surface protein that is involved in bacterial interaction with mucus and colonization of the digestive tract. The 353-kDa mature protein is representative of a broadly important class of adhesins that have remained relatively poorly characterized due to their large size and highly modular nature. MUB contains two different types of repeats (Mub1 and Mub2) present in six and eight copies, respectively, and shown to be responsible for the adherence to intestinal mucus. Here we report the 1.8-Å resolution crystal structure of a type 2 Mub repeat (184 amino acids) comprising two structurally related domains resembling the functional repeat found in a family of immunoglobulin (Ig)-binding proteins. The N-terminal domain bears striking structural similarity to the repeat unit of Protein L (PpL) from Peptostreptococcus magnus, suggesting binding in a non-immune Fab-dependent manner. A distorted PpL-like fold is also seen in the C-terminal domain. As with PpL, Mub repeats were able to interact in vitro with a large repertoire of mammalian Igs, including secretory IgA. This hitherto undetected activity is consistent with the current model that antibody responses against commensal flora are of broad specificity and low affinity.     

Grafting of protein L-binding activity onto recombinant antibody fragments

Recombinant antibody fragments consisting of variable domains can be easily produced in various host cells, but there is no universal system that can be used to purify and detect them in the free form or complexed with their antigen. Protein L (PpL) is a cell wall protein isolated from Peptostreptococcus magnus, which has been reported to interact with the V-KAPPA chain of some, but not all, antibodies. Here we grafted the V-KAPPA framework region 1 (FR1) sequence of a high-affinity PpL-binding antibody onto single-chain antibody fragments (scFvs), which have no reactivity with PpL. This substitution made it possible to purify and detect scFvs using PpL conjugates. It did not hinder scFv folding and expression in recombinant bacteria, and it did not interfere with their antigen-binding function. We also identified residue 12 as being potentially able to alter PpL binding. This study, therefore, suggests a way of engineering a PpL-binding site on any scFv without interfering with its function. This could provide a universally applicable method both for the rapid purification of functional recombinant antibody fragments and for their detection even when complexed with their antigen without requiring fusion to an epitope Flag.     

Production and characterisation of a neutralising chimeric antibody against botulinum neurotoxin A

Botulinum neurotoxins, produced by Clostridium botulinum bacteria, are the causative agent of botulism. This disease only affects a few hundred people each year, thus ranking it among the orphan diseases. However, botulinum toxin type A (BoNT/A) is the most potent toxin known to man. Due to their potency and ease of production, these toxins were classified by the Centers for Disease Control and Prevention (CDC) as Category A biothreat agents. For several biothreat agents, like BoNT/A, passive immunotherapy remains the only possible effective treatment allowing in vivo neutralization, despite possible major side effects. Recently, several mouse monoclonal antibodies directed against a recombinant fragment of BoNT/A were produced in our laboratory and most efficiently neutralised the neurotoxin. In the present work, the most powerful one, TA12, was selected for chimerisation. The variable regions of this antibody were thus cloned and fused with the constant counterparts of human IgG1 (kappa light and gamma 1 heavy chains). Chimeric antibody production was evaluated in mammalian myeloma cells (SP2/0-Ag14) and insect cells (Sf9). After purifying the recombinant antibody by affinity chromatography, the biochemical properties of chimeric and mouse antibody were compared. Both have the same very low affinity constant (close to 10 pM) and the chimeric antibody exhibited a similar capacity to its parent counterpart in neutralising the toxin in vivo. Its strong affinity and high neutralising potency make this chimeric antibody interesting for immunotherapy treatment in humans in cases of poisoning, particularly as there is a probable limitation of the immunological side effects observed with classical polyclonal antisera from heterologous species.     

Production of a mouse-human chimeric monoclonal antibody to CD20 with potent Fc-dependent biologic activity

Mouse monoclonal antibody 2H7 recognizes the CD20 cell surface phosphoprotein that is expressed in normal as well as malignant B cells. CD20 may be a useful target for therapy of B cell lymphomas, since damaged normal B cells can be replaced by their antigen-negative precursors. Monoclonal antibody 2H7 is an IgG2b (kappa) immunoglobulin which cannot mediate antibody-dependent cellular cytotoxicity with human lymphocytes or complement-dependent cytotoxicity with human serum. We have now generated a chimeric 2H7 antibody by substituting the mouse constant domains of 2H7 with the human gamma 1 and kappa domains. This new antibody has the same binding specificities as 2H7 but is highly effective in mediating antibody-dependent cellular cytotoxicity with human effector cells and complement-dependent cytotoxicity with human complement.     

Multiple germline kappa light chains generate anti-insulin B cells in nonobese diabetic mice

The highly selective nature of organ-specific autoimmune disease is consistent with a critical role for adaptive immune responses against specific autoantigens. In type 1 diabetes mellitus, autoantibodies to insulin are important markers of the disease process in humans and nonobese diabetic (NOD) mice; however, the Ag-specific receptors responsible for these autoantibodies are obscured by the polyclonal repertoire. NOD mice that harbor an anti-insulin transgene (Tg) (V(H)125Tg/NOD) circumvent this problem by generating a tractable population of insulin-binding B cells. The nucleotide structure and genetic origin of the endogenous kappa L chain (Vkappa or IgL) repertoire that pairs with the V(H)125Tg were analyzed. In contrast to oligoclonal expansion observed in systemic autoimmune disease models, insulin-binding B cells from V(H)125Tg/NOD mice use specific Vkappa genes that are clonally independent and germline encoded. When compared with homologous IgL genes from nonautoimmune strains, Vkappa genes from NOD mice are polymorphic. Analysis of the most frequently expressed Vkappa1 and Vkappa9 genes indicates these are shared with lupus-prone New Zealand Black/BINJ mice (e.g., Vkappa1-110*02 and 9-124) and suggests that NOD mice use the infrequent b haplotype. These findings show that a diverse repertoire of anti-insulin B cells is part of the autoimmune process in NOD mice and structural or regulatory elements within the kappa locus may be shared with a systemic autoimmune disease.     

Characterization of neutralizing mouse‐human chimeric and shuffling antibodies against botulinum neurotoxin A

Mouse‐human chimeric monoclonal antibodies that could neutralize botulinum neurotoxins were developed and an attempt was made to establish mouse hybridoma cell clones that produced monoclonal antibodies that neutralized botulinum neurotoxin serotype A (BoNT/A). Four clones (2–4, 2–5, 9–4 and B1) were selected for chimerization on the basis of their neutralizing activity against BoNT/A and the cDNA of the variable regions of their heavy (V_H) and light chains (V_L) were fused with the upstream regions of the constant counterparts of human kappa light and gamma 1 heavy chain genes, respectively. CHO‐DG44 cells were transfected with these plasmids and mouse‐human chimeric antibodies (AC24, AC25, AC94 and ACB1) purified to examine their binding and neutralizing activities. Each chimeric antibody exhibited almost the same capability as each parent mouse mAb to bind and neutralize activities against BoNT/A. From the chimeric antibodies against BoNT/A, shuffling chimeric antibodies designed with replacement of their V_H or V_L domains were constructed. A shuffling antibody (AC2494) that derived its V_H and V_L domains from chimeric antibodies AC24 and AC94, respectively, showed much higher neutralizing activity than did other shuffling antibodies and parent counterparts. This result indicates that it is possible to build high‐potency neutralizing chimeric antibodies by selecting and shuffling V_H and V_L domains from a variety of repertoires. A shuffling chimeric antibody might be the best candidate for replacing horse antitoxin for inducing passive immunotherapy against botulism.     

Generation of a murine single chain Fv (scFv) antibody specific for cucumber mosaic virus (CMV) using a phage display library

With the long-term goal of generating CMV-resistant transgenic plants using antibody genes, a single-chain variable fragment (scFv) antibody that binds to the cucumber mosaic virus was isolated from a scFv phage display library by four rounds of affinity selection with CMV-Mf as an antigen. The scFv has the identical binding specificity to CMV as a monoclonal antibody that is generated by the hybridoma fusion technique, and recognized purified preparations of CMV isolates belonging to either subgroup I or II in immunoblotting. The nucleotide sequences of the recombinant antibody showed that a heavy chain variable region (V(H)) gene belonged to the VH3 subgroup and the kappa light chain variable region (V kappa) came from the Vkappa4 subgroup. Our results demonstrate that the scFv phage display library, an alternative approach to the traditional hybridoma fusion technique, has a potential applicability in the study of plant virus and plant pathology.