Light Chain Dimer Research Articles

Conformational Differences in the Light Chain Constant Domain of Immunoglobulin G and Free Light Chain May Influence Proteolysis in AL Amyloidosis

Immunoglobulin light chain amyloidosis (AL) is a life-threatening disease caused by the deposition of light chain (LC) and its fragments containing variable (VL) and portions of constant (CL) domains. AL patients feature either monoclonal free LCs (FLCs) circulating as covalent and noncovalent homodimers, or monoclonal immunoglobulin (Ig) wherein the LC and heavy chain (HC) form disulfide-linked heterodimers, or both. The role of full-length Ig in AL amyloidosis is unclear as prior studies focused on FLC or VL domain. We used a mammalian cell-based expression system to generate four AL patient-derived full-length IgGs, two non-AL IgG controls, and six corresponding FLC proteins derived from an IGLV6-57 germline precursor. Comparison of proteins’ secondary structure, thermal stability, proteolytic susceptibility, and disulfide link reduction suggested the importance of local vs. global conformational stability. Analysis of IgGs vs. corresponding FLCs using hydrogen–deuterium exchange mass spectrometry revealed major differences in the local conformation/dynamics of the CL domain. In all IgGs vs. FLCs, segments containing β-strand and α-helix βAC-αACBC were more dynamic/exposed while segment βDC-βEC was less dynamic/exposed. Notably, these segments overlapped proteolysis-prone regions whose in vivo cleavage generates LC fragments found in AL deposits. Altogether, the results suggest that preferential cleavage in segments βAC-αACBC of FLC or βDC-βEC of LC in IgG helps generate amyloid protein precursors. We propose that protecting these segments using small-molecule stabilizers, which bind to the interfacial cavities CL-CL in FLC and/or CL-CH1 in IgG, is a potential therapeutic strategy to complement current approaches targeting VL-VL or VL-CL stabilization of LC dimer.

Structural, Biophysical, and Computational Studies of a Murine Light Chain Dimer.

Antibodies are widely used in medicinal and scientific research due to their ability to bind to a specific antigen. Most often, antibodies are composed of heavy and light chain domains. Under physiological conditions, light chains are produced in excess, as compared to the heavy chain. It is now known that light chains are not silent partners of the heavy chain and can modulate the immune response independently. In this work, the first crystal structure of a light chain dimer originating from mice is described. It represents the light chain dimer of 6A8, a monoclonal antibody specific to the allergen Der f 1. Building on the unexpected occurrence of this kind of dimer, we have demonstrated that this light chain is stable in solution alone. Moreover, enzyme-linked immunosorbent assays (ELISA) have revealed that, when the light chain is not partnered to its corresponding heavy chain, it interacts non-specifically with a wide range of proteins. Computational studies were used to provide insight on the role of the 6A8 heavy chain domain in the specific binding to Der f 1. Overall, this work demonstrates and supports the ongoing notion that light chains can function by themselves and are not silent partners of heavy chains.

Novel Assay for Quantification of Free Light Chain (FLC) Dimers in Serum of Patients with Plasma Cell Dyscrasias

Free light chains (FLCs) are a well-established biomarker of plasma cell dyscrasias. FLCs exist as monomers, dimers and oligomers. Lambda FLC is particularly prone to form dimers and oligomers. Under certain pathological conditions, FLC dimerization changes towards the increased dimer formation. For instance, high levels of FLC dimers were found in AL amyloidosis and multiple myeloma (MM) even when the total FLC concentrations were near the normal levels. Thus, FLC dimer quantification can be used as a tool to diagnose and monitor AL amyloidosis and MM. Here we report a novel assay to detect and quantify FLC dimers with mass spectrometry. To demonstrate the power of the assay, we quantified FLC dimers in LC-only MM serum samples and compared the results to the gold standard Freelite assay. FLC dimer quant assay relies on the detection and quantification of constant region dimeric peptides of lambda and kappa LCs in serum with targeted mass spectrometry. The serum sample is enzymatically digested under non-reducing condition for 1 hour, specific disulfide-bridged dimeric peptides are then separated by Evosep One liquid chromatography and analyzed with parallel reaction monitoring (PRM) on Orbitrap Exploris mass spectrometer. FLC dimers can be quantified relative to control serum samples and by absolute quant using stable isotope labelled (SIL) peptides resulting in mg/dL values. The identities of the peptides were confirmed by mass spectrometry analysis of synthetic dimeric peptides and recombinant FLCs. To determine the lower limit of quantification (LLoQ) the control pooled serum was spiked with the increasing amounts of recombinant FLC. The assay demonstrated exceptional linearity from 0.78 to 50 mg/dL of spiked FLC kappa or lambda (R 2=0.999 for both). The assay only requires 10 μL of serum without the need for a diagnostic sample and can be performed at any time point, as frequently as needed. FLC dimer quant assay was compared to Freelite assay for 17 newly diagnosed patients with LC-only MM. All patients underwent autologous stem cell transplant (ASCT) and had banked serum samples at diagnosis and day 100 post-ASCT. 15 patients (88%) reached CR at day 100 post-ASCT. 8 patients had lambda LC MM, while 9 patients had kappa LC MM. At diagnosis the median involved FLC was 250 mg/dL (range: 26.1 - 1440), while at day 100 post-ASCT the median involved FLC was 1.1 mg/dL (range 0 - 2.5). The FLC dimer quant results were reported as a ratio to control, whereby the FLC dimer amount in control pooled serum was set to 1. FLC dimers were detected at all time points in all patients. The median involved FLC dimer ratio to control at diagnosis was 23.3 (range: 4.5 - 445.7), while the median involved FLC dimer ratio to control at day 100 post-ASCT was 1.0 (range: 0.3 - 3.8). Strong correlation (R 2=0.993 for lambda and R 2=0.931 for kappa) was observed between FLC dimer and Freelite assays (Fig.1). To conclude, we developed a novel assay to measure FLC dimer with mass spectrometry. The assay demonstrated a good correlation to Freelite assay. This study establishes an FLC dimer assay as a promising diagnostic and monitoring tool in LC MM patients. Large clinical studies are needed to establish reference ranges for kappa and lambda dimers in healthy population and demonstrate clinical utility in other plasma cell dyscrasias.

Amino acid sequence homology of monoclonal serum free light chain dimers and tissue deposited light chains in AL amyloidosis: a pilot study.

Diagnosis of light chain amyloidosis (AL) requires demonstration of amyloid deposits in a tissue biopsy followed by appropriate typing. Previous studies demonstrated increased dimerization of monoclonal serum free light chains (FLCs) as a pathological feature of AL. To further examine the pathogenicity of FLC, we aimed at testing amino acid sequence homology between circulating and deposited light chains (LCs). Matched tissue biopsy and serum of 10 AL patients were subjected to tissue proteomic amyloid typing and nephelometric FLC assay, respectively. Serum FLC monomers (M)and dimers (D)were analyzed by Western blotting (WB) and mass spectrometry (MS). WB of serum FLCs showed predominance of either κ or λ type, in agreement with the nephelometric assay data. Abnormal FLC M-D patterns typical of AL amyloidosis were demonstrated in 8 AL-λ patients and in one of two AL-κ patients: increased levels of monoclonal FLC dimers, high D/M ratio values of involved FLCs, and high ratios of involved to uninvolved dimeric FLCs. MS of serum FLC dimers showed predominant constant domain sequences, in concordance with the tissue proteomic amyloid typing. Most importantly, variable domain sequence homology between circulating and deposited LC species was demonstrated, mainly in AL-λ cases. This is the first study to demonstrate homology between circulating FLCs and tissue-deposited LCs in AL-λ amyloidosis. The applied methodology can facilitate studying the pathogenicity of circulating FLC dimers in AL amyloidosis. The study also highlights the potential of FLC monomer and dimer analysis as a non-invasive screening tool for this disease.

A method to obtain purified free light chain monomers and dimers from urine samples of patients with multiple myeloma

Antibody light chains are synthesized in excess by plasma cells, and this excess can be secreted into biological fluids as dimers or monomers in various proportions. Structural differences between monomers or dimers of free light chains (FLC) can affect their biological functions and possibly their pathogenicity. They also may exhibit differential immune reactivity, perhaps explaining discrepant quantifications when measured by different immunoreagents. Having purified FLC monomers and dimers available can be useful for studying their properties. Here we propose a simple preparatory procedure to purify FLC monomers and dimers from urine samples of patients with plasma cell disorders. Two representative urine samples containing lambda or kappa FLC were loaded into a nonreducing sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE). The gel strips containing separate monomers and dimers were excised, electroeluted, and the FLC recovered. The FLC were recovered from SDS-PAGE gel in sufficient amounts to be quantified by UV and two automated nephelometric assays immunochemical. The procedure was found to be simple, reproducible, and with a high yield, thus offering the opportunity to compare different assays. Not all urine samples are suitable for this procedure, but this approach allows for the purification of FLC monomers and dimers from many selected urine samples which maintain their oligomeric organization.

At-line quantitative profiling of monoclonal antibody products during bioprocessing using HPLC-MS

(1) Background: The N-glycosylation profile as well as the subunit assembly of monoclonal antibodies (mAbs) are strongly dependent on manufacturing conditions and thus need to be monitored during the bioprocess. Commonly, mAbs are characterized downstream of the fermentation process applying different analytical techniques like released glycan analysis, peptide mapping, or subunit profiling. However, these procedures are time-consuming and difficult to perform in real-time. (2) Methods: We applied a simple HPLC-MS workflow with minimal sample preparation to characterize mAb product quality at the intact protein level at different time points during fermentation. After harvest, the cell culture medium was centrifuged briefly. The supernatant containing the fermentation product was diluted and immediately subjected to HPLC-MS analysis. (3) Results: Besides the product of interest (mAb), the fermentation broth contained misassembled variants, mostly light chain and light chain dimer. The mAb's glycosylation profile changed over time showing an increase in galactosylated variants with G0F/G1F being the most abundant glycoform at all time points of fermentation. Furthermore, expressed protein species were relatively and absolutely quantified. The workflow was very robust despite analyzing a highly complex matrix. Relative standard deviations for retention times were below 0.5% for both intra and inter-day comparison, whereas relative procedural standard deviations for quantification of the different protein species ranged between 7 and 13%. (4) Conclusions: This approach allows for reliable analysis of product profiles of monoclonal antibody species including misassembled subunits and glycosylation variants directly from fermentation broth using a fast and robust HPLC-MS workflow.

Amyloidogenic immunoglobulin light chain kinetic stabilizers comprising a simple urea linker module reveal a novel binding sub-site

In immunoglobulin light chain (LC) amyloidosis, the misfolding, or misfolding and misassembly of LC a protein or fragments thereof resulting from aberrant endoproteolysis, causes organ damage to patients. A small molecule “kinetic stabilizer” drug could slow or stop these processes and improve prognosis. We previously identified coumarin-based kinetic stabilizers of LCs that can be divided into four components, including a “linker module” and “distal substructure”. Our prior studies focused on characterizing carbamate, hydantoin, and spirocyclic urea linker modules, which bind in a solvent-exposed site at the VL-VL domain interface of the LC dimer. Here, we report structure–activity relationship data on 7-diethylamino coumarin-based kinetic stabilizers. This substructure occupies the previously characterized “anchor cavity” and the “aromatic slit”. The potencies of amide and urea linker modules terminating in a variety of distal substructures attached at the 3-position of this coumarin ring were assessed. Surprisingly, crystallographic data on a 7-diethylamino coumarin-based kinetic stabilizer reveals that the urea linker module and distal substructure attached at the 3-position bind a solvent-exposed region of the full-length LC dimer distinct from previously characterized sites. Our results further elaborate the small-molecule binding surface of LCs that could be occupied by potent and selective LC kinetic stabilizers.

Barriers to Small Molecule Drug Discovery for Systemic Amyloidosis.

Inhibition of amyloid fibril formation could benefit patients with systemic amyloidosis. In this group of diseases, deposition of amyloid fibrils derived from normally soluble proteins leads to progressive tissue damage and organ failure. Amyloid formation is a complex process, where several individual steps could be targeted. Several small molecules have been proposed as inhibitors of amyloid formation. However, the exact mechanism of action for a molecule is often not known, which impedes medicinal chemistry efforts to develop more potent molecules. Furthermore, commonly used assays are prone to artifacts that must be controlled for. Here, potential mechanisms by which small molecules could inhibit aggregation of immunoglobulin light-chain dimers, the precursor proteins for amyloid light-chain (AL) amyloidosis, are studied in assays that recapitulate different aspects of amyloidogenesis in vitro. One molecule reduced unfolding-coupled proteolysis of light chains, but no molecules inhibited aggregation of light chains or disrupted pre-formed amyloid fibrils. This work demonstrates the challenges associated with drug development for amyloidosis, but also highlights the potential to combine therapies that target different aspects of amyloidosis.

Characterization and elimination of artificial non-covalent light Chain dimers in reduced CE-SDS analysis of pertuzumab

Capillary electrophoresis sodium dodecyl sulfate (CE-SDS), either in reduced (rCE-SDS) or non-reduced (nrCE-SDS) form, is widely used for purity evaluation and impurity analysis of monoclonal antibody (mAb) drugs. The accuracy of the method may be interfered by artificial species resulted from sample preparation or electrophoresis operation if it is not well optimized. In a routine analysis of pertuzumab for both innovator Perjeta® and biosimilar HLX11 samples, a cluster of unknown peaks located between light chain (LC) and heavy chain (HC) were observed in rCE-SDS and making the purity of (LC + HC)% unacceptable. They can hardly be reduced by regular method optimization such as changing buffer pH, denaturing temperature or incubation time to achieve the (LC + HC)% expectation. Here, the peaks are first characterized and determined to be non-covalently formed LC-LC dimers by multiple techniques including reversed-phase liquid chromatography-mass spectrometry (LC–MS). These artifacts are then eliminated through enhancing capillary separation temperature to 60 °C and decreasing the separation voltage to 9.5 kV, an unusual CE-SDS operation setting. Finally, a developed rCE-SDS method is presented for successful evaluation of pertuzumab purity and impurities, which is further confirmed by an alternative reduced microchip-based gel electrophoresis. In summary, the developed method provided an accurate and reliable purity evaluation and size variant profiling for batch releasing, stability testing and quality study of reduced pertuzumab samples.

Structural basis for the stabilization of amyloidogenic immunoglobulin light chains by hydantoins

Misfolding and aggregation of immunoglobulin light chains (LCs) leads to the degeneration of post-mitotic tissue in the disease immunoglobulin LC amyloidosis (AL). We previously reported the discovery of small molecule kinetic stabilizers of the native dimeric structure of full-length LCs, which slow or stop the LC aggregation cascade at the outset. A predominant structural category of kinetic stabilizers emerging from the high-throughput screen are coumarins substituted at the 7-position, which bind at the interface between the two variable domains of the light chain dimer. Here, we report the binding mode of another, more polar, LC kinetic stabilizer chemotype, 3,5-substituted hydantoins. Computational docking, solution nuclear magnetic resonance experiments, and x-ray crystallography show that the aromatic substructure emerging from the hydantoin 3-position occupies the same LC binding site as the coumarin ring. Notably, the hydantoin ring extends beyond the binding site mapped out by the coumarin hits. The hydantoin ring makes hydrogen bonds with both LC monomers simultaneously. The alkyl substructure at the hydantoin 5-position partially occupies a novel binding pocket proximal to the pocket occupied by the coumarin substructure. Overall, the hydantoin structural data suggest that a larger area of the LC variable-domain–variable-domain dimer interface is amenable to small molecule binding than previously demonstrated, which should facilitate development of more potent full-length LC kinetic stabilizers.

Kappa-on-Heavy (KoH) bodies are a distinct class of fully-human antibody-like therapeutic agents with antigen-binding properties

We describe a Kappa-on-Heavy (KoH) mouse that produces a class of highly diverse, fully human, antibody-like agents. This mouse was made by replacing the germline variable sequences of both the Ig heavy-chain (IgH) and Ig kappa (IgK) loci with the human IgK germline variable sequences, producing antibody-like molecules with an antigen binding site made up of 2 kappa variable domains. These molecules, named KoH bodies, structurally mimic naturally existing Bence-Jones light-chain dimers in their variable domains and remain wild-type in their antibody constant domains. Unlike artificially diversified, nonimmunoglobulin alternative scaffolds (e.g., DARPins), KoH bodies consist of a configuration of normal Ig scaffolds that undergo natural diversification in B cells. Monoclonal KoH bodies have properties similar to those of conventional antibodies but exhibit an enhanced ability to bind small molecules such as the endogenous cardiotonic steroid marinobufagenin (MBG) and nicotine. A comparison of crystal structures of MBG bound to a KoH Fab versus a conventional Fab showed that the KoH body has a much deeper binding pocket, allowing MBG to be held 4 Å further down into the combining site between the 2 variable domains.

Systemic misfolding of immunoglobulins in the test tube and in the cell

Light chain (AL) amyloidosis is an incurable disease characterized by the misfolding, aggregation, and systemic deposition of amyloid composed of immunoglobulin light chains causing organ failure and death. We have conducted thermodynamic and fibril formation studies of both variable domain and full length (variable + constant domains) immunoglobulin proteins involved in AL amyloidosis. We have found that there is thermodynamic range -under physiological conditions- in which these proteins populate partially folded states that favor amyloid formation. Scan rate dependency in the protein unfolding reaction plays a role for a subset of these proteins, particularly full length light chains. Immunoglobulin light chains internalize as dimers and as amyloid fibrils into human cardiomyocytes via micropinocytosis in a size dependent manner. External amyloid aggregates rapidly surround the cells and act as a recruitment point for soluble protein, triggering amyloid fibril elongation. Light chain dimers cause apoptosis while amyloid fibrils cause cell growth arrest demonstrating different cytotoxic mechanisms for soluble proteins and amyloid aggregates. The cell growth arrest observed in the presence of amyloid fibrils is rescued by cell to cell contacts with mesenchymal stromal stem cells through changes in the extracellular matrix and cell adhesion pathways. In vitro amyloid formation experiments show that seeds of proteins with different sequences are able to accelerate the reaction albeit with a lower efficiency. Heterologous recruitment of light chains indicate that fibril formation is kinetically determined by the conformation of the amyloidogenic conformational precursor and modulated by the differential ability of each protein to either nucleate or elongate fibrils. Studies on the early events of fibril formation followed by different biophysical techniques have shown differences in the species formed by fast amyloid forming protein AL-09 compared to slow amyloid forming (AL-12) and control (kI) proteins indicating that the rate of formation of intermediates may vary depending on the amyloidogenic potential of the proteins. Overall, our studies emphasize the complex interactions between light chain and cells that result in fibril internalization, protein recruitment, and cytotoxicity that may occur in AL amyloidosis. Support or Funding Information NIGMS R01 GM071514, theSeidler Professorship, the Mayo Foundation, and thegenerous support of amyloidosis patients and their families External LC amyloid fibrils act as a seeding point for soluble protein. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Search for new biomarkers of pediatric multiple sclerosis: application of immunoglobulin free light chain analysis.

Identifying new biomarkers is needed to overcome the diagnostic difficulties of pediatric multiple sclerosis (MS). Recently, we developed a new technique including CSF analysis of free light chain (FLC) monomers and dimers, which can improve diagnosis of adult MS. The present study has been designed to evaluate the utility of our technique for MS diagnosis in children. Patients with MS (n=21) and non-MS demyelinating or inflammatory neurological disorders (n=35) participated in the study. MS diagnosis was based on clinical and magnetic resonance imaging (MRI) findings. Western blot analysis was applied to examine FLC in the patients' CSF and serum. FLC indices for FLC monomer and dimer levels and κ/λ ratios were estimated. The samples were also analyzed by oligoclonality test. The study revealed abnormally elevated levels of κ-FLC monomers and dimers in the CSF of 10 MS patients ("κ-type MS"). Increased amounts of λ dimers were found in six MS cases ("λ-type MS"), while high levels of both κ and λ FLC ("mixed type MS") were documented in three MS cases. MRI and clinical assessment showed a more aggressive disease form for the "mixed" and "λ-type" cases. Our method demonstrated higher sensitivity (90.5%) and specificity (91.4%) for discrimination between MS and non-MS patients, as compared to oligoclonality test (81% and 65.7%, respectively). The proposed method may significantly contribute to diagnosis and prognosis of pediatric MS.

Multiple myeloma cells' capacity to decompose H2O2 determines lenalidomide sensitivity

AbstractLenalidomide is an immunomodulatory drug (IMiDs) with clinical efficacy in multiple myeloma (MM) and other late B-cell neoplasms. Although cereblon (CRBN) is an essential requirement for IMiD action, the complete molecular and biochemical mechanisms responsible for lenalidomide-mediated sensitivity or resistance remain unknown. Here, we report that IMiDs work primarily via inhibition of peroxidase-mediated intracellular H2O2 decomposition in MM cells. MM cells with lower H2O2-decomposition capacity were more vulnerable to lenalidomide-induced H2O2 accumulation and associated cytotoxicity. CRBN-dependent degradation of IKZF1 and IKZF3 was a consequence of H2O2-mediated oxidative stress. Lenalidomide increased intracellular H2O2 levels by inhibiting thioredoxin reductase (TrxR) in cells expressing CRBN, causing accumulation of immunoglobulin light-chain dimers, significantly increasing endoplasmic reticulum stress and inducing cytotoxicity by activation of BH3-only protein Bim in MM. Other direct inhibitors of TrxR and thioredoxin (Trx) caused similar cytotoxicity, but in a CRBN-independent fashion. Our findings could help identify patients most likely to benefit from IMiDs and suggest direct TrxR or Trx inhibitors for MM therapy.

Increased Neuronal Depolarization Evoked by Autoantibodies in Diabetic Obstructive Sleep Apnea: Role for Inflammatory Protease(s) in Generation of Neurotoxic Immunoglobulin Fragment.

Obstructive sleep apnea increases in diabetes and morbid obesity. We tested a hypothesis that circulating autoantibodies in adult type 2 diabetes which increase in association with morbid obesity are capable of causing long-lasting neuronal depolarization and altered calcium release in mouse atrial cardiomyocytes. Protein-A eluates from plasma of 14 diabetic obstructive sleep apnea patients and 17 age-matched diabetic patients without sleep apnea were tested for effects on depolarization and neurite out growth in N2a mouse neuroblastoma cells. The mechanism of autoantibody-mediated neurite outgrowth inhibition was investigated in co-incubation experiments of diabetic obstructive sleep apnea autoantibodies with specific antagonists of G-protein coupled receptors or the RhoA/Rho kinase signaling pathway. Following long-term storage of the protein-A eluates (to allow spontaneous proteolysis and IgG subunit dissociation), plasma autoantibodies from diabetic obstructive sleep apnea, cancer or control patients were compared for enhancement of inhibitory effects on endothelial cell survival. Size exclusion chromatography performed (in the presence or absence of a specific membrane type 1-matrix metalloproteinase inhibitor) was used to characterize the IgG autoantibody subunit(s) or fragments associated with peak neurotoxicity in diabetic obstructive sleep apnea. Diabetic obstructive sleep apnea (n = 14) autoantibodies caused a significant increase (P = 0.01) in membrane depolarization in N2a mouse neuroblastoma cells compared to control diabetic patients (n = 15) not suffering with obstructive sleep apnea. Process extension in N2A mouse neuroblastoma cells was significantly inhibited (P = 0.01) by diabetic obstructive sleep apnea (n = 9) autoantibodies compared to effects from identical 10 μg/mL concentrations of control diabetic autoantibodies in patients without obstructive sleep apnea. Ten micromolar concentrations of SCH-202676, a G-protein coupled receptor antagonist (n = 5) or ten micromolar concentration of Y27632, a selective Rho kinase inhibitor (n = 6), each significantly prevented (P < 0.001) neurite outgrowth inhibition by diabetic obstructive sleep apnea autoantibodies. Autoantibodies in representative patients with obstructive sleep apnea and either atrial fibrillation or left ventricular hypertrophy evoked acute large increases in intracellular Ca2+ in HL-1 mouse atrial cardiomyocytes. The magnitude of intracellular Ca2+ release was dose-dependently significantly correlated to the electrocardiographic Cornell voltage-duration product. Gel filtration of diabetic obstructive sleep apnea autoantibodies revealed peak neurotoxicity associated with MWs corresponding to IgG light chain dimer(s), monomers or half-light chains as well as a novel ∼ 5.5 kD putative light chain fragment. These results suggest that diabetic obstructive sleep apnea autoantibodies may induce strong depolarization in neuronal cells and alter Ca2+ signaling in atrial cardiomyocytes consistent with a role in pathophysiology in subsets of diabetic obstructive sleep apnea having co-morbid atrial fibrillation or another clinically significant cardiac rhythm disturbance.

The Kinetic Stability of a Full-Length Antibody Light Chain Dimer Determines whether Endoproteolysis Can Release Amyloidogenic Variable Domains

Light chain (LC) amyloidosis (AL amyloidosis) appears to be caused by the misfolding, or misfolding and aggregation of an antibody LC or fragment thereof and is fatal if untreated. LCs are secreted from clonally expanded plasma cells, generally as disulfide-linked dimers, with each monomer comprising one constant and one variable domain. The energetic contribution of each domain and the role of endoproteolysis in AL amyloidosis remain unclear. To investigate why only some LCs form amyloid and cause organ toxicity, we measured the aggregation propensity and kinetic stability of LC dimers and their associated variable domains from AL amyloidosis patients and non-patients. All the variable domains studied readily form amyloid fibrils, whereas none of the full-length LC dimers, even those from AL amyloidosis patients, are amyloidogenic. Kinetic stability—that is, the free energy difference between the native state and the unfolding transition state—dictates the LC's unfolding rate. Full-length LC dimers derived from AL amyloidosis patients unfold more rapidly than other full-length LC dimers and can be readily cleaved into their component domains by proteases, whereas non-amyloidogenic LC dimers are more kinetically stable and resistant to endoproteolysis. Our data suggest that amyloidogenic LC dimers are kinetically unstable (unfold faster) and are thus susceptible to endoproteolysis that results in the release amyloidogenic LC fragments, whereas other LCs are not as amenable to unfolding and endoproteolysis and are therefore aggregation resistant. Pharmacologic kinetic stabilization of the full-length LC dimer could be a useful strategy to treat AL amyloidosis.

Toxic Immunoglobulin Light Chain Autoantibodies are Associated with a Cluster of Severe Complications in Older Adult Type 2 Diabetes.

To assess neuronal depolarization evoked by autoantibodies in diabetic depression compared to depolarization evoked by autoantibodies in control patients. To determine whether a subset of severe (late-onset) diabetic complications may be mediated in part by toxic immunoglobulin light chains that may increase in diabetic nephropathy. Protein-A eluates from plasma of 21 diabetic depression patients and 37 age-matched controls were tested for depolarization in hippocampal or immature neurons. Subsets of depolarizing or non-depolarizing autoantibodies were tested for neurite outgrowth inhibition in N2A neuroblastoma cells or the ability to modulate Ca2+ release in HL-1 atrial cardiomyocytes or in endothelial cells. The stability of depolarizing autoantibodies was investigated by heat treatment (56°C × 30 minutes) or following prolonged exposure to the pro-protein convertase, furin. Gel filtration of active depolarizing autoantibodies was performed to determine the apparent molecular mass of peak neurotoxicity associated with the autoantibodies. Diabetic depression (n = 21) autoantibodies caused significantly greater mean depolarization in neuroblastoma cells (P < 0.01) compared to autoantibodies in diabetic (n = 15) or non-diabetic (n = 11) patients without depression. Depolarizing autoantibodies caused significantly more (P=0.011) inhibition of neurite outgrowth in neuroblastoma cells than non-depolarizing autoantibodies (n = 10) and they evoked sustained, global intracellular Ca2+ release in atrial cardiomyocytes or in endothelial cells. A subset of older diabetic patients suffering with a cluster of nephropathy, non-ischemic cardiomyopathy and/or depression demonstrated the presence of stable light chain dimers having apparent MW of 46 kD and associated with peak neurotoxicity in neuroblastoma cells. These data suggest that autoantibodies in older adult diabetic depression cause long-lasting depolarization in hippocampal neurons including adult dentate gyrus neural progenitor cells. The autoantibodies may impair adult dentate gyrus neurogenesis associated with treatment-refractory depression via several mechanisms including suppression of neurite outgrowth, and alteration of membrane excitability. Stable, toxic light chain autoantibody components may contribute to a cluster of severe (late-onset) complications characterized by dysfunction in highly vascularized tissues.

Probing the role of λ6 immunoglobulin light chain dimerization in amyloid formation

Light chain amyloidosis (AL) is a lethal disease associated with the deposition of misfolded immunoglobulin light chains (LC) as amyloid fibrils in the extracellular space of vital organs. The exact mechanisms of LC self-assembly and the molecular basis leading to cellular and organ failure still remain poorly understood. In this study, we investigated the relationship between the quaternary structure, the stability and the amyloidogenecity of LC variable domain (VL) from the λ6 germline. We observed that the amyloidogenic λ6 Wil and its non-amyloidogenic counterpart Jto dimerize in a concentration-dependent manner and that the dimer affinity is considerably decreased in the presence of a high ionic strength. Our results showed that the dimeric state delays the structural conversion associated with amyloid formation and that the monomer is critical to initiate amyloidogenesis. Thermal and chemical unfolding studies revealed that the dimeric state of VL λ6 has an equivalent stability to the monomer. This indicates that the protective effect of dimerization is not related to thermodynamic stability but, most likely, resides in specific structural features. The toxicity of monomeric Jto and Wil as well as fibrillar aggregates was evaluated on cardiomyoblasts and ThT-negative proteospecies reduced cellular viability when employed at high concentration. This study provides novel insights into the complex process of LC amyloidogenesis and suggests that dimer stabilization constitutes a promising strategy to prevent self-assembly and amyloid deposition.

A rapid method for simultaneous evaluation of free light chain content and aggregate content in culture media of Chinese hamster ovary cells expressing monoclonal antibodies for cell line screening

The goal of developing a monoclonal antibody (mAb) production process is high productivity and high quality. Because the productivity and quality of mAbs depend on cell line properties, the selection of cell lines suitable for large-scale production is an important stage in process development for mAb production. The light chain (LC) is important for antibody folding and assembly in the endoplasmic reticulum; cell lines that secrete a large amount of LCs in the medium secrete high-quality antibodies with high productivity. LC contents in culture media have been estimated by western blotting, reverse-phase high-performance liquid chromatography, and enzyme-linked immunosorbent assay. However, these analyses require fine tuning of experimental conditions for each antibody analyzed. Here we report a rapid and simple high-sensitivity size-exclusion chromatography (HS-SEC) method to evaluate the contents of low-molecular weight species (LMWS, mainly consisting of LC monomers and dimers) and high-molecular weight species (HMWS, aggregates) in the media for cell line screening. Because LMWS and HMWS are important indicators of productivity and quality, respectively, for cell line screening, HS-SEC will be useful in the first step of cell line selection needed for large-scale production.

Evaluation of strategies to control Fab light chain dimer during mammalian expression and purification: A universal one-step process for purification of correctly assembled Fab.

Fabs are an important class of antibody fragment as both research reagents and therapeutic agents. There are a plethora of methods described for their recombinant expression and purification. However, these do not address the issue of excessive light chain production that forms light chain dimers nor do they describe a universal purification strategy. Light chain dimer impurities and the absence of a universal Fab purification strategy present persistent challenges for biotechnology applications using Fabs, particularly around the need for bespoke purification strategies. This study describes methods to address light chain dimer formation during Fab expression and identifies a novel CH 1 affinity resin as a simple and efficient one-step purification for correctly assembled Fab.