A novel method of preparing the monoform structure of catalytic antibody light chain

Structural and thermodynamic insights into antibody light chain tetramer formation through 3D domain swapping

Overexpression of antibody light chains in small plasma cell clones can lead to misfolding and aggregation. On the other hand, the formation of amyloid fibrils from antibody light chains is related to amyloidosis. Although aggregation of antibody light chain is an important issue, atomic-level structural examinations of antibody light chain aggregates are sparse. In this study, we present an antibody light chain that maintains an equilibrium between its monomeric and tetrameric states. According to data from X-ray crystallography, thermodynamic and kinetic measurements, as well as theoretical studies, this antibody light chain engages in 3D domain swapping within its variable region. Here, a pair of domain-swapped dimers creates a tetramer through hydrophobic interactions, facilitating the revelation of the domain-swapped structure. The negative cotton effect linked to the β-sheet structure, observed around 215 nm in the circular dichroism (CD) spectrum of the tetrameric variable region, is more pronounced than that of the monomer. This suggests that the monomer contains less β-sheet structures and exhibits greater flexibility than the tetramer in solution. These findings not only clarify the domain-swapped structure of the antibody light chain but also contribute to controlling antibody quality and advancing the development of future molecular recognition agents and drugs.

Obtaining Highly Active Catalytic Antibodies Capable of Enzymatically Cleaving Antigens

A catalytic antibody has multiple functions compared with a monoclonal antibody because it possesses unique features to digest antigens enzymatically. Therefore, many catalytic antibodies, including their subunits, have been produced since 1989. The catalytic activities often depend on the preparation methods and conditions. In order to elicit the high catalytic activity of the antibodies, the most preferable methods and conditions, which can be generally applicable, must be explored. Based on this view, systematic experiments using two catalytic antibody light chains, #7TR and H34, were performed by varying the purification methods, pH, and chemical reagents. The experimental results obtained by peptidase activity tests and kinetic analysis, revealed that the light chain's high catalytic activity was observed when it was prepared under a basic condition. These data imply that a small structural modulation of the catalytic antibody occurs during the purification process to increase the catalytic activity while the antigen recognition ability is kept constant. The presence of NaCl enhanced the catalytic activity. When the catalytic light chain was prepared with these preferable conditions, #7TR and H34 hugely enhanced the degradation ability of Amyloid-beta and PD-1 peptide, respectively.

A new catalytic site functioning in antigen cleavage by H34 catalytic antibody light chain

The cleavage reactions of catalytic antibodies are mediated by a serine protease mechanism involving a catalytic triad composed of His, Ser, and Asp residues, which reside in the variable region. Recently, we discovered a catalytic antibody, H34 wild type (H34wt), that is capable of enzymatically cleaving an immune-check point PD-1 peptide and recombinant PD-1; however, H34wt does not contain His residues in the variable region. To clarify the reason behind the catalytic features of H34wt and the amino acid residues involved in the catalytic reaction, we performed site-directed mutagenesis focusing on the amino acid residues involved in the cleavage reaction, followed by catalytic activity tests, immunological reactivity evaluation, and molecular modeling. The results revealed that the cleavage reaction by H34wt proceeds through the action of a new catalytic site composed of Arg, Thr, and Gln. This new scheme differs from that of the serine protease mechanism of catalytic antibodies.

A new algorithm to convert a normal antibody into the corresponding catalytic antibody

Over thousands of monoclonal antibodies (mAbs) have been produced so far, and it would be valuable if these mAbs could be directly converted into catalytic antibodies. We have designed a system to realize the above concept by deleting Pro⁹⁵, a highly conserved residue in CDR-3 of the antibody light chain. The deletion of Pro⁹⁵ is a key contributor to catalytic function of the light chain. The S35 and S38 light chains have identical amino acid sequences except for Pro⁹⁵. The former, with Pro⁹⁵ did not show any catalytic activity, whereas the latter, without Pro⁹⁵, exhibited peptidase activity. To verify the generality of this finding, we tested another light chain, T99wt, which had Pro⁹⁵ and showed little catalytic activity. In contrast, a Pro⁹⁵-deleted mutant enzymatically degraded the peptide substrate and amyloid-beta molecule. These two cases demonstrate the potential for a new method of creating catalytic antibodies from the corresponding mAbs.

New technologies to introduce a catalytic function into antibodies: A unique human catalytic antibody light chain showing degradation of β-amyloid molecule along with the peptidase activity

Since the discovery of a natural catalytic antibody in 1989, many catalytic antibodies targeting peptides, nucleotides, virus and bacterial proteins, and many molecules have been prepared. Although catalytic antibodies should have features superior to non-catalytic monoclonal antibodies, the reports on catalytic antibodies are far fewer than those on normal (non-catalytic) antibodies. Nowadays, we can obtain any monoclonal antibody we want, which is not the case for catalytic antibodies. To overcome this drawback of catalytic antibodies, much basic research must be done. As one way to attain this purpose, we have been making a protein bank of human antibody light chains, in which the light chains were expressed, purified, and stored for use in screening against many kinds of antigen, to then get clues to introducing a catalytic function in normal antibodies. As the number of stored light chains in the above protein bank has reached the hundreds, in this study, we screened them against amyloid-beta (Aβ), which is well-known as one of the molecules causing Alzheimer's disease. We found two interesting light chains, #7TR and #7GY. The former could degrade both a fluorescence resonance energy transfer-Aβ substrate and Aβ1-40 full peptide. In contrast, #7GY, whose sequence is identical to that of #7TR except for the amino acids at the 29th and 30th positions, did not degrade the FRET-Aβ substrate at all. By using a synthetic substrate, Arg-pNA, the difference between the chemical features of the two light chains was investigated in detail. In addition, we found that the presence of Zn(II) ion hugely influenced the catalytic activity of the #7TR light chain but not #7GY. Through these facts and the discussion, we propose one of the clues to how to put a catalytic function in a normal (non-catalytic) antibody.

Catalase activity of IgG antibodies from the sera of healthy donors and patients with schizophrenia

We present first evidence showing that some electrophoretically homogeneous IgGs from the sera of patients with schizophrenia (36.4%) and their Fab and F(ab)2 fragments as well as from healthy donors (33.3%) possess catalase activity. The relative catalase activity of IgGs from the sera of individual schizophrenia patients (and healthy donors) significantly varied from patient to patient, but the activity of IgGs from healthy donors is on average 15.8-fold lower than that for schizophrenia patients. After extensive dialysis of purified IgGs against EDTA chelating metal ions, the relative catalase activity of IgGs decreases on average approximately 2.5-3.7-fold; all IgGs possess metal-dependent and independent catalase activity. The addition of external Me2+ ions to dialyzed and non-dialyzed IgGs leads to a significant increase in their activity. The best activator of dialyzed and non-dialyzed IgGs is Co2+, the activation by Cu2+, Mn2+, and Ni2+ ions were rare and always lower than by Co2+. Every IgG preparation demonstrates several individual sets of very well expressed pH optima in the pH range from 4.0 to 9.5. These data speak for the individual repertoire of catalase IgGs in every person and an extreme diversity of abzymes in their pH optima and activation by different metal ions. It is known that antioxidant enzymes such as superoxide dismutases, catalases, and glutathione peroxidases represent critical defense mechanisms preventing oxidative modifications of DNA, proteins, and lipids. Catalase activity of human IgGs could probably also play a major role in the protection of organisms from oxidative stress and toxic compounds.

Role of the constant region domain in the structural diversity of human antibody light chains

Issues regarding the structural diversity (heterogeneity) of an antibody molecule have been the subject of discussion along with the development of antibody drugs. Research on heterogeneity has been extensive in recent years, but no clear solution has been reached. Heterogeneity is also observed in catalytic antibody κ light chains (CLs). In this study, we investigated how the constant region domain of CLs concerns structural diversity because it is a simple and good example for elucidating heterogeneity. By means of cation-exchange chromatography, SDS-PAGE, and 2-dimensional electrophoresis for the CL, multimolecular forms consisting of different electrical charges and molecular sizes coexisted in the solution, resulting in the similar heterogeneity of the full length of CLs. The addition of copper ion could cause the multimolecular forms to change to monomolecular forms. Copper ion contributed greatly to the enrichment of the dimer form of CL and the homogenization of the differently charged CLs. Two molecules of the CL protein bound one copper ion. The binding affinity of the ion was 48.0 μM^-1 Several divalent metal ions were examined, but only zinc showed a similar effect.-Hifumi, E., Taguchi, H., Kato, R., Uda, T. Role of the constant region domain in the structural diversity of human antibody light chains.