Idiotypic network mimicry and antibody catalysis: lessons for the elicitation of efficient anti-idiotypic protease antibodies

Catalytic Antibodies: Design, Expression, and Their Applications in Medicine

Catalytic antibodies made it feasible to develop new catalysts, which had previously been the subject of research. Scientists have discovered natural antibodies that can hydrolyze substrates such as nucleic acids, proteins, and polysaccharides during decades of research, as well as several ways of producing antibodies with specialized characteristics and catalytic functions. These antibodies are widely used in chemistry, biology, and medicine. Catalytic antibodies can continue to play a role and even fully prevent the emergence of autoimmune disorders, especially in the field of infection and immunity, where the process of its occurrence and development often takes a long time. In this work, the development, design and evolution methodologies, and the expression systems and applications of catalytic antibodies, are discussed. Trial registration: not applicable.

Catalytic antibodies and their applications in biotechnology: state of the art

Catalytic antibodies are immunoglobulins endowed with enzymatic properties. Discovered in the second part of the 1980s, the enthusiasm they initially aroused was counterbalanced by the difficulty of their production and their low catalytic rates. Nevertheless, improvements in expression systems and engineering technologies, combined with various studies suggesting that catalytic antibodies play a role in the immune system, have opened the way to new applications for these proteins. Herein we review catalytic antibodies from a biotechnological point of view, focusing our study on the different production methods, expression systems and their potential clinical applications dedicated to these proteins.

Strategies for the selection of catalytic antibodies against organophosphorus nerve agents

Among the strategies aimed at biocompatible means for organophosphorus nerve agents neutralization, immunoglobulins have attracted attention in the 1990's and 2000's both for their ability to immobilize the toxicants, but also for their ability to be turned into enzymatically active antibodies known as catalytic antibodies or abzymes (antibodies--enzymes). We will present here a critical review of the successive strategies used for the selection of these nerve agent-hydrolyzing abzymes, based on hapten design, namely antibodies raised against a wide variety of transition state analogs, and eventually the strategies based on anti-idiotypic antibodies and reactibodies.

Organization and evolution of synthetic idiotypic networks

We introduce a class of weighted graphs whose properties are meant to mimic the topological features of idiotypic networks, namely, the interaction networks involving the B core of the immune system. Each node is endowed with a bit string representing the idiotypic specificity of the corresponding B cell, and the proper distance between any couple of bit strings provides the coupling strength between the two nodes. We show that a biased distribution of the entries in bit strings can yield fringes in the (weighted) degree distribution, small-world features, and scaling laws, in agreement with experimental findings. We also investigate the role of aging, thought of as a progressive increase in the degree of bias in bit strings, and we show that it can possibly induce mild percolation phenomena, which are investigated too.

Molecular imprint of enzyme active site by camel nanobodies: rapid and efficient approach to produce abzymes with alliinase activity

Screening of inhibitory Ab1 antibodies is a critical step for producing catalytic antibodies in the anti-idiotypic approach. However, the incompatible surface of the active site of the enzyme and the antigen-binding site of heterotetrameric conventional antibodies become the limiting step. Because camelid-derived nanobodies possess the potential to preferentially bind to the active site of enzymes due to their small size and long CDR3, we have developed a novel approach to produce antibodies with alliinase activities by exploiting the molecular mimicry of camel nanobodies. By screening the camelid-derived variable region of the heavy chain cDNA phage display library with alliinase, we obtained an inhibitory nanobody VHHA4 that recognizes the active site. Further screening with VHHA4 from the same variable domain of the heavy chain of a heavy-chain antibody library led to a higher incidence of anti-idiotypic Ab2 abzymes with alliinase activities. One of the abzymes, VHHC10, showed the highest activity that can be inhibited by Ab1 VHHA4 and alliinase competitive inhibitor penicillamine and significantly suppressed the B16 tumor cell growth in the presence of alliin in vitro. The results highlight the feasibility of producing abzymes via anti-idiotypic nanobody approach.

Catalytic digestion of human tumor necrosis factor-α by antibody heavy chain

It has long been an important task to prepare a catalytic antibody capable of digesting a targeting crucial protein that controls specific life functions. Tumor necrosis factor-α (TNF-α) is a cytokine and an important molecule concerned with autoimmune diseases such as rheumatoid arthritis, chronic obstructive pulmonary disease, and Crohn's disease. A mAb (ETNF-6 mAb) raised against human TNF-α was prepared, and the steric conformation was created by using molecular modeling after the cDNA was sequenced. The heavy chain (ETNF-6-H) of the mAb was considered to possess a catalytic triad-like structure in the complementarity determining regions (CDRs). As a result, ETNF-6-H exhibited a peptidase and a protease activity. In fact, ETNF-6-H predominantly cleaved the Ser5-Arg6 bond of TNF-α at the first step, resulting in the generation of a fragment of ∼ 17 kDa. This fragment was digested to a smaller molecule of 15 kDa by scission of the Gln21-Ala22 bond. The intermediate product was further converted into a fragment of 13.3 kDa by successive cleavage of the Leu36-Leu37 and Asn39-Gly40 bonds. The heavy chain possessed a protease activity against TNF-α with a multicleavage site.

Physiopathology of catalytic antibodies: the case for factor VIII-hydrolyzing immunoglobulin G

Antibodies that are able to catalyze the antigen for which they are specific are produced spontaneously by the immune system. Catalytic immunoglobulins (Igs) both of the IgM and IgG isotypes have been detected in the serum of healthy donors, where they have been proposed to participate in the removal of metabolic waste and in the defense of the organism against invading pathogens. Conversely, antigen-specific hydrolytic IgG have been reported in a number of inflammatory, autoimmune and neoplastic disorders: their pathogenic effects have been demonstrated occasionally. The pathophysiological relevance of catalytic antibodies thus remains an elusive issue. Through the description of the pro-coagulation factor VIII as a model target antigen for catalytic antibodies, we propose that catalytic antibodies have either a beneficial or a deleterious role depending on the physiopathological context. Physiology thus relies on a delicate equilibrium between the levels of soluble target antigen and that of antigen-specific hydrolyzing immunoglobulins. Indeed, in patients with hemophilia A, in whom endogenous factor VIII is deficient or missing and exogenous factor VIII needs to be administered to treat hemorrhagic events, the development of factor VIII-hydrolyzing IgG that inactivate the therapeutically administered factor VIII, may reveal deleterious. In contrast, in a situation in which excess factor VIII may be detrimental and lead to excessive coagulation, disseminated thrombosis and organ ischemia, as seen in severe sepsis, our recent data suggest that the presence of factor VIII-hydrolyzing IgG may be beneficial to the patient.

Anti-idiotypic antibody mimics proteolytic function of parent antigen

Functional imaging of subtilisin Carlsberg active center by the idiotypic network yielded a catalytic anti-idiotypic antibody with endopeptidase, amidase, and esterase activities. A monoclonal antibody inhibitory to subtilisin (Ab1 5-H4) was employed as the template for guiding the idiotypic network to produce the catalytic anti-idiotypic Ab2 6B8-E12. Proteolytic activity of 6B8-E12 was demonstrated by zymography using self-quenched fluorescein-BSA conjugate and in a coupled assay detecting Ab2-dependent RNase A inactivation. Cleavage of peptide substrates by 6B8-E12 revealed distinct patterns of hydrolysis with high preference for aromatic residues before or after the scissile bond. Catalytic activity of Ab2 was inhibited by phenylmethylsulfonyl fluoride, a mechanism-based inhibitor of serine hydrolases. 5-H4 and 6B8-E12 were cloned, produced in Escherichia coli as single-chain variable fragments (scFvs), and purified. Kinetic parameters for amidolytic and esterolytic activities were similar in Ab2 and its scFv derivative. Although the antigen-specific portion of 6B8-E12 possesses no primary structure similarity to subtilisin, it mimics proteolytic and amidolytic functions of the parental antigen, albeit with 4 orders of magnitude slower acceleration rates. The lack of detectable endopeptidase activity of 6B8-E12 scFv raises interesting issues concerning general evolution of catalytic activity. The in silico 3D models of Ab1 and Ab2 revealed strong structural similarity to known anti-protease antibodies and to abzymes, respectively. These results indicate that the idiotypic network is capable, to a significant extent, of reproducing catalytic apparatus of serine proteases and further validate the use of imaging of enzyme active centers by the immune system for induction of abzymes accelerating energy-demanding amide bond hydrolysis.

Design of a serine protease-like catalytic triad on an antibody light chain displayed on the yeast cell surface

Lc-WT, the wild-type light chain of antibody, and Lc-Triad, its double mutant with E1D and T27aS designing for the construction of catalytic triad within Asp1, Ser27a, and original His93 residues, were displayed on the cell surface of the protease-deficient yeast strain BJ2168. When each cell suspension was reacted with BODIPY FL casein and seven kinds of peptide-MCA substrates, respectively, a remarkable difference in hydrolytic activities toward Suc-GPLGP-MCA (succinyl-Gly-Pro-Leu-Gly-Pro-MCA), a substrate toward collagenase-like peptidase, was observed between the constructs: Lc-Triad-displaying cells showed higher catalytic activity than Lc-WT-displaying cells. The difference disappeared in the presence of the serine protease inhibitor diisopropylfluorophosphate, suggesting that the three amino acid residues, Ser27a, His93, and Asp1, functioned as a catalytic triad responsible for the proteolytic activity in a similar way to the anti-vasoactive intestinal peptide (VIP) antibody light chain. A serine protease-like catalytic triad (Ser, His, and Asp) is considered to be directly involved in the catalytic mechanism of the anti-VIP antibody light chain, which moderately catalyzes the hydrolysis of VIP. These results suggest the possibility of new approach for the creation of tailor-made proteases beyond limitations of the traditional immunization approach.

Catalytic autoantibodies in clinical autoimmunity and modern medicine

Abzymes (catalytic autoantibodies) belong to an absolutely new group of physiologically active substances with dual characteristics: they represent a pool of canonical autoantibodies and possess catalytic activity. Among them, proteolytic and DNA-hydrolyzing autoantibodies are of special value. Abzymes are an important pathogenic factor in the progression of clinical autoimmunity syndrome. The presence of autoantibodies against various autoantigens is accompanied by their high catalytic potential. The increase in this activity correlates with serum levels of the autoantibodies, clinical manifestations of autoimmune disorders, disease severity and the rate of progressing disability. Abzymes are crucial for immune homeostasis regulation. They can be of practical value in the development of modern immunodiagnostic tools and schedules of immunotherapy.

Induction of a protein-targeted catalytic response in autoimmune prone mice: antibody-mediated cleavage of HIV-1 glycoprotein GP120

We have induced a polyclonal IgG that degrades the HIV-1 surface antigen, glycoprotein gp120, by taking advantage of the susceptibility of SJL mice to a peptide-induced autoimmune disorder, experimental autoimmune encephalomyelitis (EAE). Specific pathogen-free SJL mice were immunized with structural fragments of gp120, fused in-frame with encephalitogenic peptide MBP(85-101). It has resulted in a pronounced disease-associated immune response against antigens. A dramatic increase of gp120 degradation level by purified polyclonal IgG from immunized versus nonimmunized mice has been demonstrated by a newly developed fluorescence-based assay. This activity was inhibited by anti-mouse immunoglobulin antibodies as well as by Ser- and His-reactive covalent inhibitors. A dominant proteolysis site in recombinant gp120 incubated with purified polyclonal IgG from immunized mice was shown by SDS-PAGE. The SELDI-based mass spectrometry revealed that these antibodies exhibited significant specificity toward the Pro484-Leu485 peptide bond. The sequence surrounding this site is present in nearly half of the HIV-I variants. This novel strategy can be generalized for creating a catalytic vaccine against viral pathogens.

Pathophysiology of catalytic antibodies

Immunoglobulins have initially been illustrated as proteins produced by the immune system for binding and neutralizing foreign molecules potentially harmful to the organism. The number of V(H), D(H), J(H), V(L) and J(L) genes that encode the variable regions of immunoglobulins and the junctional diversity that occurs at the time of somatic rearrangement determine the extent of the repertoire of antibodies that may be potentially produced by an organism. This potential repertoire includes antibodies the antigen binding site of which may recognize external as well as autologous antigens, or may structurally resemble the active site of enzymes and be endowed with enzymatic activity. Under physiological conditions, B cell clones that produce antibodies naturally endowed with catalytic activity are negatively regulated and subjected to apoptosis. Catalytic antibodies are expressed only following active immunization, or if the physiological regulatory mechanisms that control the expression of catalytic antibody-producing B cell clones are perturbed, e.g. in the context of pregnancy or in the course of autoimmune diseases.

A catalytic antibody heavy chain HpU-2 degrading its epitope peptide and H. pylori urease

The HpU-2 monoclonal antibody (mAb) raised against Helicobacter pylori urease mainly recognized the alpha-subunit of the urease. On the other hand, the heavy chain of HpU-2 mAb (HpU-2-H) isolated from the parent mAb recognized both the alpha- and beta-subunit, in which the beta-subunit was recognized more strongly than the beta-subunit. HpU-2-H cleaved a peptide, SVELIDIGGNRRIFGFNALVD, which is the epitope sequence recognized by HpU-2 mAb, showing a double-phase reaction profile at 25 degrees C in a phosphate buffer. After an induction time of 24h, the cleavage of the peptide was initiated by HpU-2-H at a high rate and it was completed at 80 h of incubation. By mass spectroscopy, two main fragmented peptides, SVELIDIGGNRR and SVELIDIGGNRRIFG, were identified. In addition, many small peptide fragments were produced by successive cleavage of the fragmented peptides. Cleavage tests for H. pylori urease by HpU-2-H revealed that the beta-subunit of the urease was cleaved first and completely decomposed at 20 h of incubation. Cleavage of the alpha-subunit started after the complete decomposition of the beta-subunit. These cleavage results were in good agreement with the immunological features of HpU-2-H. The irrelevant proteins, BSA and HSA, were hardly cleaved by HpU-2-H.

Autoantibodies to myelin basic protein catalyze site-specific degradation of their antigen

Autoantibody-mediated tissue destruction is among the main features of organ-specific autoimmunity. This report describes "an antibody enzyme" (abzyme) contribution to the site-specific degradation of a neural antigen. We detected proteolytic activity toward myelin basic protein (MBP) in the fraction of antibodies purified from the sera of humans with multiple sclerosis (MS) and mice with induced experimental allergic encephalomyelitis. Chromatography and zymography data demonstrated that the proteolytic activity of this preparation was exclusively associated with the antibodies. No activity was found in the IgG fraction of healthy donors. The human and murine abzymes efficiently cleaved MBP but not other protein substrates tested. The sites of MBP cleavage determined by mass spectrometry were localized within immunodominant regions of MBP. The abzymes could also cleave recombinant substrates containing encephalytogenic MBP(85-101) peptide. An established MS therapeutic Copaxone appeared to be a specific abzyme inhibitor. Thus, the discovered epitope-specific antibody-mediated degradation of MBP suggests a mechanistic explanation of the slow development of neurodegeneration associated with MS.

Induction of covalent binding antibodies

Covalent interactions between antibody combining site residues and substrates have been implicated in the catalytic activity of abzymes elicited by design or occurring naturally in autoimmune disease. In this study, the potential for covalent binding by antibodies (Abs) was investigated by the induction of immune responses against molecules presenting chemically reactive haptenic groups. Immunogenic conjugates containing a phosphonate diester or a pyruvate carbonyl group were used to elicit antibodies that could specifically react with the electrophilic moieties. Products formed by covalent binding were detected by a western blot technique or by differential ELISA on reduced or unreduced carbonyl haptens. Antisera to the diphenylphosphonate contained antibodies with covalent reactivity, which increased with immunization. The reactivity was specific to the anti-phosphonate response and not to control immune sera induced against the unmodified carrier protein. Reactivity was focused on the antibody light (L) chain. Antisera to the phenylpyruvate hapten appeared to bind strongly to proteins modified by the carbonyl group hapten. However, anti-carrier antisera and non-immune sera had similar reactivity, indicating that the pyruvate moiety reacts nonspecifically with immunoglobulins. This suggested that affinity maturation of antibodies for reversible binding through hemiacetal or Schiff base adducts with antigens requires a less reactive carbonyl in the antigen. On the other hand, the induction of antibodies with enhanced nucleophilic reactivity toward phosphonate esters implies that irreversible binding to the B cell receptor can drive clonal expansion and antibody selection. These results support a designer strategy for generating nucleophilic abzymes and could also account for the occurrence of chemically reactive or catalytic antibodies in natural immunity or autoimmunity.

Super catalytic antibody and antigenase

By immunizing ground-state peptides or proteins, we can produce super catalytic antibodies possessing serine protease-like characteristics. The unique feature of super catalytic antibodies is their ability to decompose a target molecule that is being killed. The authors have succeeded in preparing super catalytic antibodies that destroy (i) the HIV-1 envelope protein gp41, (ii) chemokine receptor CCR5 peptide, and (iii) Helicobacter pylori urease, etc. Some of them can degrade antigens at high catalytic reaction rates. Regarding their Km and kcat, super catalytic antibodies show intermediary values between that of enzymes (high Km and kcat) and that of antibodies (low Km and kcat [=0]). The catalytic function of an antibody mostly resides in its light chain. From mouse Vkappa germline analysis, it became clear that super catalytic antibodies are generated from some discrete germlines such as bb1, cr1, cs1, bl1, bj2 and bd2. In these Vkappa germlines, at least one catalytic triad composed of three amino acid residues, namely, Asp1, Ser27a and His93, is encoded. Namely, the antibody light chains (super catalytic antibodies) generated from the germlines are inherently able to enzymatically decompose antigens. Thus, such antibody light chains can be referred to as antigenase (antigen-decomposing enzyme) and may have arisen during the evolution of antibodies to acquire a higher ability than that of enzymes for developing a sophisticated self-defense system for survival.

Specific degradation of H. pylori urease by a catalytic antibody light chain

Catalytic antibodies capable of digesting crucial proteins of pathogenic bacteria have long been sought for potential therapeutic use. Helicobacter pylori urease plays a crucial role for the survival of this bacterium in the highly acidic conditions of human stomach. The HpU-9 monoclonal antibody (mAb) raised against H. pylori urease recognized the alpha-subunit of the urease, but only slightly recognized the beta-subunit. However, when isolated both the light and the heavy chains of this antibody were mostly bound to the beta-subunit. The cleavage reaction catalyzed by HpU-9 light chain (HpU-9-L) followed the Michaelis-Menten equation with a K(m) of 1.6 x 10(-5) m and a k(cat) of 0.11 min(-1), suggesting that the cleavage reaction was enzymatic. In a cleavage test using H. pylori urease, HpU-9-L efficiently cleaved the beta-subunit but not the alpha-subunit, indicating that the degradation by HpU-9-L had a specificity. The cleaved peptide bonds in the beta-subunit were L121-A122, E124-G125, S229-A230, Y241-D242, and M262-A263. BSA was hardly cleaved by HpU-9-L, again indicating the digestion by HpU-9-L was specific. In summary, we succeeded in the preparation of a catalytic antibody light chain capable of specifically digesting the beta-subunit of H. pylori urease.

Investigation of active form of catalytic antibody light chain 41S-2-L

We have raised a monoclonal antibody (41S-2) against the conserved sequence, RGPDRPEGIEEEGGERDRD, of human immunodeficiency virus type1 (HIV-1) envelope gp41. That antibody light chain (41S-2-L) cleaves gp41-derived peptide (TPRGPDRPEGIEEEGGERDRD; TP41-1) with a characteristic biphasic profile composed of induction and active phases. It is considered that the conformation of 41S-2-L is changed, by such as induced fitting, to move to active phase to decompose the antigenic peptide during the induction phase. In order to investigate what happens to 41S-2-L in the induction and active phase, the cleavage reaction of the peptide by 41S-2-L was examined in detail from the viewpoint of kinetic and spectroscopic analysis. The kinetic data showed that the preferable conformational transition of 41S-2-L took place by the unimolecular reaction of 41S-2-L in the induction phase. UV-vis and fluorescence spectroscopic analysis suggested that the conformational transition leads to the generation of aggregates of 41S-2-L in the reacting solution, which causes the huge enhancement of the catalytic activity of 41S-2-L. The nuclei of the aggregates may be formed in the induction phase. The aggregates and soluble 41S-2-L are considered to be in chemical equilibrium during the cleavage reaction of the antigen.

Catalytic antibody light chain capable of cleaving a chemokine receptor CCR-5 peptide with a high reaction rate constant

A monoclonal antibody (MAb), ECL2B-2, was obtained by immunizing a peptide possessing a part of a sequence of a chemokine receptor, CCR-5, which is present as a membrane protein on the macrophage surface, and which plays an important role in human immunodeficiency virus (HIV) infection. From the DNA and the deduced amino acid sequences of the light and heavy chains of ECL2B-2 MAb, molecular modeling was conducted to calculate the steric conformation of the antibody. Modeling suggested that the structure of ECL2B-2 could possess one or two catalytic triad(s), composed of Asp(1), Ser(27a) (or Ser(27e)), and His(93) (or His(27d)), in the light chain of ECL2B-2. The three amino acid residues, Asp(1), Ser(27a), and His(93), are identical to those of catalytic antibody light chains such as VIPase and i41SL1-2. The light chain of ECL2B-2 MAb degraded the antigenic peptide CCR-5 within about 100 h. Surprisingly, the light chain had a very high catalytic reaction rate constant (k(cat)) of 2.23 min(-1), which is greater by factors of tens to hundreds than those of natural catalytic antibodies obtained previously. The heavy chain of ECL2B-2 MAb, which has no catalytic triad because of a lack of His residue, did not degrade the CCR-5 peptide.

Catalytic features of monoclonal antibody i41SL1-2 subunits

A monoclonal antibody (mAb), i41SL1-2, was obtained by immunizing the peptide of complementarity-determining region-1 (CDRL-1: RSSKSLLYSNGNTYLY) of a super catalytic antibody light chain, 41S-2-L, capable of enzymatically destroying the gp41 molecule of the HIV-1 envelope. From the DNA and the deduced amino acid sequences of the light and heavy chain of i41SL1-2 mAb, molecular modeling was conducted that suggested that both subunits of i41SL1-2 mAb possess catalytic triads in their structures. Especially the light chain of i41SL1-2 mAb possesses a characteristic catalytic triad composed of Asp(1), Ser(27A), and His(93), whose positions are identical to the catalytic antibody light chain, VIPase, of S. Paul and colleagues (see text). The antibody gene of i41SL1-2 light chain and VIPase belong to the same germline, bd2, suggesting that the discrete germline inherently possesses catalytic activity. Both light and heavy chains of i41SL1-2 mAb degraded the antigenic peptide CDRL-1 within 47 and 57 h, respectively. The catalytic reaction constant (kcat) of the light and heavy chain was 6.1 x 10(-1) and 6.2 x 10(-1) min(-1), respectively. These are high values for the natural catalytic antibodies reported so far. The catalytic efficiency (kcat/Km) of the light and heavy chain was 3.1 x 10(5) and 4.9 x 10(4) M(-1) min(-1), respectively. The first cleaved bond of the antigenic peptide by subunits of i41SL1-2 mAb was between Arg(1) and Ser(2) in the sequence of CDRL-1, suggesting a serine protease character.

Selection of peptides inhibiting a beta-lactamase-like activity

A library of random peptide sequences was used to select peptides that inhibit an anti-idiotypic catalytic Ig, immunoglobulin (IgG) 9G4H9, with a beta-lactamase-like activity. This library displays cyclic heptapeptides on the surface of bacteriophages and represents a collection of up to 4.5 x 109 peptides. The first selection step aimed at enriching the library in species that bind to the whole Ig molecule. The second step was to discriminate peptides that bind to part of the molecule other than the active site. Selected peptides were then screened by surface plasmon resonance analysis. Those displaying measurable Kd values were assayed for their ability to inhibit the catalytic Ig.

Endopeptidase character of monoclonal antibody i41-7 subunits

We prepared six anti-idiotypic monoclonal antibodies (mAbs) against parent 41S-2 mAb whose light chain is a super catalytic antibody (41S-2-L) capable of degrading targeted HIV-1gp41 molecule. Out of the obtained six mAbs, i41-7 mAb showed the strongest affinity to the parent 41S-2 mAb. The three dimensional structure of i41-7 mAb was created by molecular modeling using the deduced amino acid sequence of the light and heavy chain of i41-7 mAb. It suggests that the light and heavy chain possess catalytic triad-like structure composed of Ser, His and Asp in their conformations. Both chains of i41-7 mAb could cleave peptide bond of some peptides such as a polypeptide, TP41-1 (TPRGPDRPEGIEEEGGERDRD), as anticipated. The cleaving reaction advanced in accordance with Michaelis-Menten equation. The catalytic efficiency (kcat/Km) of light and heavy chain was 9.1 x 10(3) and 1.7 x 10(4) M(-1) x min(-1), respectively, while the intact i41-7 mAb did not exhibit any catalytic activity. The first cleaved bond of the TP41-1 peptide by the light chain was between 14E and 15G in the sequence. It was revealed that both light and heavy chains had endopeptidase characteristics.