A glycosylated Bence Jones protein and its autologous amyloid light chain containing potentially amyloidogenic residues

Role of the mechanisms for antibody repertoire diversification in monoclonal light chain deposition disorders: when a friend becomes foe

The adaptive immune system of jawed vertebrates generates a highly diverse repertoire of antibodies to meet the antigenic challenges of a constantly evolving biological ecosystem. Most of the diversity is generated by two mechanisms: V(D)J gene recombination and somatic hypermutation (SHM). SHM introduces changes in the variable domain of antibodies, mostly in the regions that form the paratope, yielding antibodies with higher antigen binding affinity. However, antigen recognition is only possible if the antibody folds into a stable functional conformation. Therefore, a key force determining the survival of B cell clones undergoing somatic hypermutation is the ability of the mutated heavy and light chains to efficiently fold and assemble into a functional antibody. The antibody is the structural context where the selection of the somatic mutations occurs, and where both the heavy and light chains benefit from protective mechanisms that counteract the potentially deleterious impact of the changes. However, in patients with monoclonal gammopathies, the proliferating plasma cell clone may overproduce the light chain, which is then secreted into the bloodstream. This places the light chain out of the protective context provided by the quaternary structure of the antibody, increasing the risk of misfolding and aggregation due to destabilizing somatic mutations. Light chain-derived (AL) amyloidosis, light chain deposition disease (LCDD), Fanconi syndrome, and myeloma (cast) nephropathy are a diverse group of diseases derived from the pathologic aggregation of light chains, in which somatic mutations are recognized to play a role. In this review, we address the mechanisms by which somatic mutations promote the misfolding and pathological aggregation of the light chains, with an emphasis on AL amyloidosis. We also analyze the contribution of the variable domain (V_L) gene segments and somatic mutations on light chain cytotoxicity, organ tropism, and structure of the AL fibrils. Finally, we analyze the most recent advances in the development of computational algorithms to predict the role of somatic mutations in the cardiotoxicity of amyloidogenic light chains and discuss the challenges and perspectives that this approach faces.

Antibodies gone bad - the molecular mechanism of light chain amyloidosis

Light chain amyloidosis (AL) is a systemic disease in which abnormally proliferating plasma cells secrete large amounts of mutated antibody light chains (LCs) that eventually form fibrils. The fibrils are deposited in various organs, most often in the heart and kidney, and impair their function. The prognosis for patients diagnosed with AL is generally poor. The disease is set apart from other amyloidoses by the huge number of patient-specific mutations in the disease-causing and fibril-forming protein. The molecular mechanisms that drive the aggregation of mutated LCs into fibrils have been enigmatic, which hindered the development of efficient diagnostics and therapies. In this review, we summarize our current knowledge on AL amyloidosis and discuss open issues.

ALkappa(I) (UNK) - primary structure of an AL-amyloid protein presenting an organ-limited subcutaneous nodular amyloid syndrome of long duration. Case report and review

Slowly progressing subcutaneous nodules all over the body were detected in 1994 in an otherwise healthy, now 66-year-old woman (UNK). A first biopsy was taken 10 years ago and revealed amyloid. Immunohistochemistry was suggestive for ALkappa. From a nodular excisate, performed in the same year for cosmetic reasons, amyloid fibrils were extracted. Protein separation according to their size revealed multiple protein fragments below the MW of an intact kappa-light chain. They were identified as kappa-fragments by Western blotting. The kappa-fragments were cleaved into overlapping peptides using tryptic, N-Asp and chymotryptic digests. Peptides were sequenced by Edman-degradation and mass spectrometry. The complete amino acid sequence of the variable region and most of the constant region of ALkappa (UNK) was identified in various fragments comprising positions 1 to 207 of a monoclonal kappa(I)-light chain. Four novel and several rare amino acid exchanges have been identified as compared to 17 amyloidogenic and >100 non-amyloidogenic kappa(I)-sequences published, leading to increased hydrophobicity of ALkappa (UNK). Sequence analysis of C-region peptides allowed one to determine the kappa-allotype as being invb(+). A rabbit antibody was produced against ALkappa(I) (UNK). It strongly reacted with amyloid on formalin-fixed paraffin embedded tissue sections of the same patient and detected ALkappa-amyloid of many other patients. In contrast, antibodies produced against kappaBJP of subclasses kappa(I)-kappa(IV) failed to label ALkappa (UNK) amyloid deposits. The patient continues to be free of systemic disease, already for 14 years until today.

Heterogeneity in primary structure, post-translational modifications, and germline gene usage of nine full-length amyloidogenic kappa1 immunoglobulin light chains

Immunoglobulin light chain amyloidosis is a protein misfolding disease in which a monoclonal immunoglobulin (Ig) light chain (LC) with a critically folded beta-conformation self-aggregates to form highly ordered, nonbranching amyloid fibrils. The insoluble nature of amyloid fibrils ultimately results in the extracellular deposition of the LC in tissues and organs throughout the body. Structural features that confer amyloidogenic properties on an Ig LC likely include amino acid sequence variations and post-translational modifications, but the specific natures of these changes remain to be defined. As part of an exploration of the effective range of amyloidogenic modifications, this study details the structural and genetic analyses of nine kappa1 LC proteins. Urinary LCs were purified by size exclusion chromatography using FPLC, and structural analyses were performed by electrospray ionization, matrix-assisted laser desorption/ionization, and tandem mass spectrometry. RT-PCR amplification, cloning, and sequencing of the monoclonal LC genes were accomplished using bone marrow-derived mRNA. Clinical data were reviewed retrospectively. Characterization of the urinary kappa1 LCs revealed extensive post-translational modification in all proteins, in addition to somatic mutations expected on the basis of results from genetic analyses. Post-translational modifications included disulfide-linked dimerization, S-cysteinylation, glycosylation, fragmentation, S-sulfonation, and 3-chlorotyrosine formation. Genetic analyses showed that several LC variable region germline gene donors were represented including O18/O8, O12/O2, L15, and L5. Clinical features included soft tissue, cardiac, renal, and hepatic involvement. This study demonstrated the extensive heterogeneity in primary structure, post-translational modifications, and germline gene usage that occurred in nine amyloidogenic kappa1 LC proteins.

Kappa III immunoglobulin light chain origin of localized orbital amyloidosis

Isolated orbital amyloidosis is a rare condition in which intra-muscular deposits result in proptosis and restriction of eye movement. Previous reports have suggested an immunoglobulin origin of the amyloid fibrils, but this has not been proven biochemically. A case is presented in which initial unilateral orbital amyloidosis progressed to bilateral disease. Biochemical analysis of resected ocular muscle determined that the amyloid fibrils were derived from a kappa III immunoglobulin light chain. Questions of pathogenesis and tissue tropism are considered.

Multiple invertebrate lysozymes in blue mussel (Mytilus edulis)

Initial analyses of lysozyme activities in individual blue mussels Mytilus edulis indicated variations in features of activity from the crystalline style to the remaining body parts (the soft body). Two separate larger scale lysozyme isolations were performed employing extracts from 1000 styles and 50 soft bodies, respectively. The soft body origin contained one, or one major, lysozyme that was purified to homogeneity. This 13 kDa protein, designated bm-lysozyme, was sequence-analysed and found to represent the product of a recently published invertebrate-type lysozyme gene from M. edulis. Three additional lysozymes were isolated from the style extract and one of them was fully purified. All four lysozymes showed different profiles of enzymatic features such as responses to pH, ionic strengths and divalent cations. From the results and the profound differences demonstrated we believe that the observed multiple forms of lysozyme activities in blue mussel reflect multiple genes instead of individual lysozyme variants and that the lysozymes serve different functions in the blue mussel.

Advanced glycation end product-modified beta2-microglobulin is a component of amyloid fibrils of primary localized cutaneous nodular amyloidosis

Primary localized cutaneous nodular amyloidosis is a rare form of cutaneous amyloidosis. Amyloid fibrils in primary localized cutaneous nodular amyloidosis have been reported to be originated from immunoglobulin light chains. Immunohistochemical studies on the lesional skins of four patients with primary localized cutaneous nodular amyloidosis demonstrated that amyloid deposits of all cases showed a positive reaction with the antibodies for beta2-microglobulin and advanced glycation end products as well as immunoglobulin light chain (kappa or lambda). No beta2-microglobulin and advanced glycation end product immunoreactivity was found in the amyloid deposits of other primary localized cutaneous amyloidosis (lichen amyloidosis and macular amyloidosis). Double immunofluorescence study of the lesional skin of primary localized cutaneous nodular amyloidosis showed that anti-kappa light chain, anti-beta2-microglobulin and anti-advanced glycation end product antibodies mostly reacted with the same area of amyloid deposit. Amyloid proteins were sequentially extracted with distilled water from one case of primary localized cutaneous nodular amyloidosis and recovered in the five water-soluble fractions (fractions I-V). Immunoblot assay of amyloid fibril proteins demonstrated that immunoreactive polypeptides with anti-kappa light chain antibody (29 kDa) and with anti-beta2-microglobulin antibody (12 kDa) were detected in fractions I-V, whereas immunoreactive polypeptide with anti-advanced glycation end product antibody (12 kDa) was detected exclusively in fractions III-V but not in fractions I and II. Two-dimensional polyacrylamide gel electrophoresis revealed that 12 kDa polypeptide in fractions I and II was electrophoretically identical with authentic beta2-microglobulin and that beta2-microglobulin in fractions III-V was advanced glycation end product-modified beta2-microglobulin with more acidic pI value. These results indicate that beta2-microglobulin is another major component of amyloid fibrils in primary localized cutaneous nodular amyloidosis and that beta2-microglobulin in primary localized cutaneous nodular amyloidosis is partly subjected to the modification of advanced glycation end product.

Protein aggregation

Protein aggregation occurs in vivo as a result of improper folding or misfolding. Diverse diseases arise from protein misfolding and are now grouped under the term "protein conformational diseases", including most of the neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, the prion encephalopathies and Huntington's disease, as well as cystic fibrosis, sickle cell anemia and other less common conditions. The hallmark event in these diseases is a change in the secondary and/or tertiary structure of a normal, functional protein, leading to the formation of protein aggregates with various supramolecular organizations. In most cases the aggregates are organized in structurally well-defined fibrils forming amyloid deposits. The crucial feature of the amyloidogenic proteins is their structural instability induced either by mutations, post-translational modifications, or local conditions, such as pH, temperature, and co-solutes. The conformational change may promote the disease either by gain of a toxic activity or by the lack of biological function of the natively folded protein. As different molecular mechanisms are involved in the formation of the various forms of protein aggregates, the laboratory diagnostic approach remains frequently elusive.

Identification and location of a cysteinyl posttranslational modification in an amyloidogenic kappa1 light chain protein by electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry

Amyloid-deposited light chain (AL) amyloidosis is correlated with the overproduction of a monoclonal immunoglobulin light chain protein by a B-lymphocyte clone. Since the amyloid fibril deposits in AL amyloidosis most often consist of the N-terminal fragments of the light chain, the majority of studies have focused on the determination of the primary structure of the protein, and reducing agents have been used routinely in the initial purification process. In this study, two light chain proteins were isolated and purified, without reduction, from the urine of a patient diagnosed with kappa 1 (kappa1) AL amyloidosis. One protein had a relative molecular mass of 12,000 and the other 24,000. Electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry, in combination with enzymatic digestions, were used to verify the amino acid sequences and identify and locate posttranslational modifications in these proteins. The 12-kDa protein was confirmed to be the N-terminal kappa1 light chain fragment (variable region) consisting of residues 1-108 or 1-109 and having one disulfide bond. The 24-kDa protein was determined to be the intact kappa1 light chain containing a cysteinyl posttranslational modification at Cys214 and disulfide bonds located at Cys23-Cys88, Cys134-Cys194, and Cys214-Cys. The methods used in this report enable high-sensitivity determination of amino acid sequence and variation in intact and truncated light chains as well as posttranslational modifications. This approach facilitates consideration of the effect of cysteinylation on the native protein structure and the potential involvement of this modification in AL amyloidosis.

Glycosylation of immunoglobulin light chains associated with amyloidosis

AL amyloidosis is a fatal disease caused by deposition of immunoglobulin light chains in a fibrillarforin (AL) in various organs. By searching the Kabat database of immunoglobulin sequences using the KabatMan software, we have shown that there is a preponderance of the consensus glycosylation sequon (AsnXxxSer/Thr) in the framework regions of amyloid light chains. We have characterised by computer graphics simulations, NMR spectroscopy and carbohydrate biochemistry the structure and conformation of the oligosaccharide from amyloid protein AL MS (lamba1) and from the amyloid associated Bence Jones protein of patient MH (kappa1). These proteins have glycosylation in the hypervariable complementarity-determining region versus framework region, respectively. Both contained a 2-6 sialylated core fucosylated biantennary chain mostly with bisecting GIcNAc. Together our results suggest that light chain glycosylation may be one of several modifications which may render the protein more prone to amyloid formation.

Four structural risk factors identify most fibril-forming kappa light chains

Antibody light chains (LCs) comprise the most structurally diverse family of proteins involved in amyloidosis. Many antibody LCs incorporate structural features that impair their stability and solubility, leading to their assembly into fibrils and to their subsequent pathological deposition when produced in excess during multiple myeloma and primary amyloidosis. The particular amino acid variations in antibody LCs that account for fibril formation and amyloidogenesis have not been identified. This study focuses on amyloidogenesis within the kappa1 family of human LCs. Reanalysis of the current database of primary structures of proteins from more than 100 patients who produced kappa1 LCs, 37 of which were amyloidogenic, reveals apparent structural features that may contribute to amyloidosis. These features include loss of conserved residues or the gain of particular residues through mutation at sites involving a repertoire of approximately 20% of the amino acid positions in the light chain variable domain (V(L)). Moreover 80% of all kappa1 amyloidogenic V(L)s are identifiable by the presence of at least one of three single-site substitutions or the acquisition of an N-linked glycosylation site through mutations. These findings suggest that it is feasible to predict fibril propensity by analysis of primary structure.

Review: immunoglobulin light chain amyloidosis--the archetype of structural and pathogenic variability

AL amyloidosis is caused by deposition in target tissue of amyloid fibrils constituted by monoclonal immunoglobulin light chains. The amyloidogenic plasma cells derive from a transformed memory B cell that can be identified by anti-idiotype monoclonal antibodies. Comparison of the primary structures of amyloidogenic and nonamyloidogenic light chains does not show any common structural motif in the amyloidogenic variants but reveals peculiar replacements which can destabilize the folding state. Reduced folding stability now appears to be a unifying property of amyloidogenic light chains. The tendency of these proteins to populate a partially unfolded intermediate state is a key event in the self-association that progresses to the formation of oligomers and fibrils. The mechanism of organ damage caused by AL amyloid deposition is not known, but clinical findings suggest that the process of amyloid fibril formation itself exerts tissue toxic effects independently of the amount of amyloid deposited. Since the disease is caused by the neoplastic expansion of the plasma cell population synthesizing the amyloidogenic light chains, the clone represents the prime therapeutic target of conventional chemotherapy and experimental immunotherapy. In common with other types of amyloidosis the therapeutic strategy can take advantage of drugs able to improve the reabsorption of the amyloid deposits or able to bind and stabilize the light chain in the native-like folded state.

The amino acid sequence of a monoclonal gamma 3-heavy chain from a patient with articular gamma-heavy chain deposition disease

Abnormal deposition of proteins, including monoclonal immunoglobulin gamma-heavy chains, may cause tissue damage and organ dysfunction. We here report the amino acid sequence of the free gamma-heavy chains present in serum and urine of the first reported case (patient G. L.) of synovial heavy chain deposition disease. The protein was heavily deleted and consisted of the hinge, in addition to the CH2 and CH3 domains, in a dimeric form, thus lacking its variable domain as well as the CH1 domain. The sequence was consistent with the gamma 3 subclass (gamma 3GL). Gm typing revealed the gamma 3 allotypes G3m(b0) and G3m(b1) in accordance with the residues Pro123, Phe128, Thr171 and Phe268 in gamma 3GL. Furthermore, the gamma 3GL molecule was glycosylated at Asn in position 129. Finally, the gamma 3GL protein was shown to contain a typical binding site for the first complement component, C1q, namely the residues Glu150, Lys152 and Lys154, with the potential of binding and activating complement, causing tissue damage following deposition.

Glycoxidative modification of AA amyloid deposits in renal tissue

BACKGROUND

N(epsilon)-carboxymethyllysine (CML) is a product of the oxidative modification of glycated proteins, which damages proteins with ageing, diabetes, uraemia and Alzheimer's disease. In contrast, pyrraline is one of the advanced glycation end products, which is independent of oxidative processes. CML has been identified in beta-amyloid of Alzheimer's disease and beta(2)-microglobulin-associated amyloid. We investigated whether CML and pyrraline are formed in AA and AL amyloid of the kidney.

METHOD

Renal specimens from 19 cases of AA amyloidosis and 14 cases of AL amyloidosis were investigated for immunolocalization of CML, pyrraline, collagen type IV and laminin in amyloid deposits. Renal biopsies of 10 age-matched cases with thin basement membrane disease and normal renal function were used as controls. The fractional areas of amyloid, CML, laminin and collagen IV in glomeruli and interstitium (%amyloid, %CML, %laminin and %collagen, respectively) were calculated using the point counting method. The correlation between these parameters was evaluated using Spearman's rank correlation test.

RESULTS

CML colocalized with AA amyloid, but not AL amyloid, except in two cases of the latter with a long history of nephropathy exceeding 14 years. In contrast, pyrraline was not observed in either type of amyloid. Mean %CML in AA amyloid was significantly higher than %collagen and %laminin in glomeruli and interstitium, indicating that AA amyloid is modified by CML independent of colocalized extracellular matrix. %CML significantly correlated with %amyloid both in glomeruli and interstitium in AA amyloidosis. AL amyloid cases with a long history of nephropathy showed positive staining for CML in glomeruli and interstitium but no staining for collagen IV and laminin in amyloid deposits.

CONCLUSION

CML modification may occur in amyloid deposits of AA amyloidosis, independent of extracellular matrix components. Glycoxidative modification may have a functional link to AA amyloid deposition in renal tissues.

Protein purification and gene isolation of chlamysin, a cold-active lysozyme-like enzyme with antibacterial activity

An antibacterial approximately 11 kDa protein designated chlamysin was isolated from viscera of the marine bivalve Chlamys islandica. Chlamysin inhibited the growth of all Gram-positive and Gram-negative bacteria tested. The isolated protein was highly efficient in hydrolyzing Micrococcus luteus cells only at low pH (4.5-6.2) and at low temperature (4-35 degrees C). No significant loss of enzyme activity was observed after 30 days storage at room temperature or after heating to 70 degrees C for 15 min, suggesting relatively high protein structure stability. Sequence-analyzed fragments of the protein revealed data which guided the isolation of the cDNA gene, encoding a 137 amino acid chlamysin precursor in scallops. The deduced protein contains a high portion of cysteine, serine and histidine residues and has a predicted isoelectric point below 7. The chlamysin protein was found to have sequence homology to an isopeptidase and to a recently published bivalve lysozyme.

Electrophoretic analysis of Bence Jones proteinuria

The electrophoresis of Bence Jones proteinuria (BJP) by urinary protein electrophoresis (UPE), immunoelectrophoresis (IE), immunofixation electrophoresis (IFE), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing (IEF), two-dimensional electrophoresis (2-DE) and capillary electrophoresis (CE) is described. UPE, IE and IFE are briefly discussed as clinical laboratory methods for the detection and typing of free light chain (LC) whilst the high resolution electrophoretic methods (SDS-PAGE, IEF, 2-DE and CE) are considered in greater detail as research tools for molecular characterisation of free LC and its association with nephrotoxicity. Refinements of sample processing designed to improve the standardisation of analysis of BJP by high resolution electrophoretic methods are reported.

Organ-Specific (Localized) Synthesis of Ig Light Chain Amyloid

Ig amyloidosis is usually a systemic disease with multisystem involvement. However, in a significant number of cases amyloid deposition is limited to one specific organ. It has not been determined if the Ig light chain (LC) amyloid precursor protein in localized amyloidosis is synthesized by circulating plasma cells with targeting of the amyloid fibril-forming process to one specific organ, or whether the synthesis of Ig LC and fibril formation occurs entirely as a localized process. In the present study local synthesis of an amyloid fibril precursor LC was investigated. Amyloid fibrils were isolated from a ureter that was obstructed by extensive infiltration of the wall with amyloid. Amino acid sequence analysis of the isolated fibril subunit protein proved it to be derived from a λII Ig LC. Plasma cells within the lesion stained positively with labeled anti-λ Ab and by in situ hybridization using an oligonucleotide probe specific for λ-LC mRNA. RT-PCR of mRNA extracted from the tumor and direct DNA sequencing gave the nucleotide sequence coding specifically for the λII amyloid subunit protein, thus confirming local synthesis of the LC protein.