The amino-acid sequence of the variable region of a carbohydrate-containing amyloid fibril protein EPS (immunoglobulin light chain, type lambda)

N-glycosylation of monoclonal light chains on routine MASS-FIX testing is a risk factor for MGUS progression

Our group previously demonstrated that M-protein light chain (LC) glycosylation can be detected on routine MASS-FIX testing. Glycosylation is increased in patients with immunoglobulin light chain amyloidosis (AL) and rarely changes over the course of a patient’s lifetime. To determine the rates of progression to AL and other plasma cell disorders (PCDs), we used residual serum samples from the Olmsted monoclonal gammopathy of undetermined significance (MGUS) screening cohort. Four-hundred and fourteen patients with known MGUS were tested by MASS-FIX, and 25 (6%) were found to have glycosylated light chains (LCs). With a median follow-up of surviving patients of 22.2 years, the 20-year progression rates to a malignant PCD were 67% (95% CI 29%, 84%) and 13% (95% CI 9%, 18%) for patients with and without glycosylated LCs, respectively. The risk of progression was independent of Mayo MGUS risk score. The respective rates of progression to AL at 20-years were 21% (95% CI 0.0, 38%) and 3% (95% CI 0.6%, 5.5%). In summary, monoclonal LC glycosylation is a potent risk factor for progression to AL, myeloma, and other PCDs, an observation which could lead to earlier diagnoses and potentially reduced morbidity and mortality.

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.

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.

Mutational Analysis in Murine Models for Myeloma-Associated Fanconi’s Syndrome or Cast Myeloma Nephropathy

We have designed an in vivo model in which murine hybridoma cell clones producing human Ig light chains (LC) are administred to mice. Depending on which monoclonal LC is expressed, this model mimicks either cast myeloma nephropathy or the pathological condition defined as myeloma-associated Fanconi’s syndrome (FS) with LC crystallization. Morphological alterations of the kidney cells are thus obtained in mice. All studied LC are closely related human monoclonal VκI proteins, which differ by a limited number of substitutions within the variable region. In the case of an FS monoclonal LC, we show that limited changes introduced through site-directed mutagenesis in the variable domain may suppress formation of intracellular crystals within tubular cells. We also show that multiple peculiarities of the variable region are simultaneously needed to allow LC crystallization; this property thus likely results from a unique LC tridimensional conformation imposed by concomitant somatic mutations of a specific germinally encoded framework.

Structural relationship of lambda-type light chains with AL amyloidosis

Three human amyloidogenic Bence Jones proteins, NIG76 VlambdaII, NIG204 VlambdaI, and NIG250 VlambdaV, were characterized. In a comparative study, three amino acids, Ser-25a, Thr-68, and Val-95, were found to be common to amyloidogenic proteins of the VlambdaII subgroup. NIG204 had an insertion of Pro residue following position 30 (30a). Proteins having an insertion at this position are invariantly amyloidogenic. NIG250 had a characteristic VlambdaV VL domain, with Mcg+ and KERN+ CL domain isotypes. Following the protein DEL, this is the second example of this subgroup. No common residue is found in the other subgroup proteins but unique substitutions do occur. It would seem that any substitution that causes an alteration in the protein conformation may lead to its being more prone to association with the amyloid processes.

Molecular characterization of the human immunoglobulin V lambda I germline gene repertoire

To advance our understanding of the human immunoglobulin V lambda germline gene contribution to normal as well as autoimmune responses, we have isolated and sequenced six germline genes of the V lambda I subgroup. These genes can be divided into three sub-subgroups on the basis of greater than or equal to 93% nucleotide sequence homology and greater than or equal to 88% deduced amino acid sequence similarity. Examination of all cDNA and protein sequences available for expressed V lambda I genes supports the assignment of these three sub-subgroups. Sequence comparisons also suggest that germline gene members of two of these sub-subgroups, I-a and I-b, are preferentially utilized in the expressed V lambda I repertoire. This finding may be at least partially attributable to regulatory sequence abnormalities apparent in two of the other V lambda I germline genes (Humlv101 and Humlv104) which may interfere with their expression.

Complementary DNA sequence of human amyloidogenic immunoglobulin light-chain precursors

The primary structure of three amyloid precursor light chains was deduced from the sequence of complementary DNA (cDNA) from bone marrow cells from patients affected with classical lambda (patient Air) or kappa (patient Arn) amyloidosis and from a patient (Aub) in whom lambda amyloid deposits were unusual by their perimembranous location in the kidney glomerulus. All three RNAs were of normal size, as estimated by Northern blotting, and encoded normal-sized light chains. The deduced light-chain sequence from patient Arn was related to the V kappa 1 subgroup, and included ten residues that had not been previously reported at these positions, only one of which (Leu-21) was located in a beta-sheet (4-2). The unusual presence of Asn-70 determined a potential N-glycosylation site. The sequence of the light chain from patient Air belonged to the V lambda 1 subgroup, and included three unusually located amino acid residues, one of which had already been reported in an amyloidogenic lambda-chain. The sequence of the light chain from patient Aub was related to the V lambda 3 subgroup, and contained five amino acid residues that had not previously been described at the corresponding positions; two of them (His-36 and Ser-77) were located in beta-sheets (3-1 and 4-3 respectively). This sequence was also peculiar because of the presence of numerous acidic residues in the complementarity-determining regions. Such unusual primary structures might be responsible for the amyloidogenic properties of these light-chain precursors.

Structure of a monoclonal kappa chain of the V kappa IV subgroup in the kidney and plasma cells in light chain deposition disease

That structural abnormalities may be responsible for nonamyloid immunoglobulin (Ig) light chain deposition disease (LCDD) is suggested by previous results of Ig biosynthesis studies, but this hypothesis was not documented at the molecular level. We report on the first complete primary sequence deduced from cDNA analysis of a kappa light chain responsible for LCDD associated with an apparently nonsecretory myeloma. Bone marrow myeloma cells contained intracellular kappa chains and no heavy chains by immunofluorescence. Kidney biopsy showed typical nonamyloid PAS-positive kappa chain deposits. SDS-PAGE analysis of material extracted from a kidney biopsy specimen and of Ig produced by the myeloma cells revealed kappa chains of abnormally high apparent molecular mass (30,000). Comparison of the NH2-terminal aminoacid sequence of the kappa chain deposited in the kidney and of the complete sequence of several identical kappa cDNA clones from bone marrow cells showed the identity of the tissue deposited and plasma cell kappa chain. The kappa mRNA had an overall normal structure and corresponded to the V kappa IV gene rearranged to J kappa 1 and followed by a normal constant exon of the Km(3) allotype. The variable sequence differed from the V kappa IV germline gene by nine point mutations, including an Asp----Asn substitution at position +70 resulting in a potential N-glycosylation site. In vitro biosynthesis experiments and treatment with N-glycosidase provided evidence for the intracellular glycosylation of the monoclonal kappa chain. The peculiar sequence and the glycosylation of a kappa chain of the rare V kappa IV subgroup might be responsible for structural abnormalities leading to tissue deposition.

Definition of the human immunoglobulin variable lambda (IGLV) gene subgroups

Comparison of 60 human immunoglobulin variable lambda (IGLV) sequences allowed us to define seven subgroups designated V lambda I to V lambda VII. We demonstrate that all lambda proteins sequenced so far fall into the subgroups I, II, III and VI, and that the lambda regions previously assigned to subgroups IV and V belong, in fact, to subgroups III and II, respectively. Four sequences not belonging to any of the subgroups I, II, III and VI define the new subgroups IV, V and VII. Interestingly, these subgroups show a higher homology to rabbit or mouse V lambda genes than to the other human V lambda subgroups. By comparison of the proteins either with the sequences deduced from the germ-line genes or with the consensus sequences, the rate of amino acid changes due to somatic mutations or allelic variations was evaluated in several lambda proteins. Framework and complementarity-determining regions of the human IGLV genes and proteins were delineated. Alignment of the lambda sequences shows that functional V-J rearrangement occurs, with or without deletion of nucleotides encoding one or two amino acids at the 3' end of the V gene. Diversity of the third complementarity-determining region is due to somatic mutations and to flexible V-J junction, but there is no evidence of N-diversity in the human lambda locus.

The primary structure of the variable region of an immunoglobin IV light-chain amyloid-fibril protein (AL GIL)

The primary structure of the variable region of an amyloid-fibril protein GIL of immunoglobulin lambda-light-chain origin (AL) was determined. The AL protein obtained from the fibrils in the spleen of a 54-year-old man with primary systemic amyloidosis could be assigned to subgroup IV of the lambda variable-region sequence. About 50% of the protein was found to be truncated in the N-terminus and lacked the first six amino acid residues. The polypeptides consisted of about 146 amino acid residues and contained traces of carbohydrate. An acceptor site for N-glycosylation was found in positions 90-93, but no glycopeptide could be isolated. Comparison of the amino acid sequence of AL protein GIL with that of the only Bence-Jones protein of subgroup IV previously studied revealed a sequence homology of 89%. A similar comparison made with other AL proteins gave sequence homologies below 66%.

Is the formation of AL-type amyloid promoted by structural peculiarities of immunoglobulin L-chains? Primary structure of an amyloidogenic lambda-L-chain (BJP-ZIM)

A Bence-Jones protein (Protein ZIM) was isolated from the urine of a patient with myeloma-associated amyloidosis. The amino-acid sequence of the variable region of the carboxymethylated protein was established by automatic stepwise degradation of the enzymatically deblocked protein and tryptic peptides thereof. The protein is of the lambda-type of human immunoglobulin L-chains and is closely homologous to subgroup I. In the course of the tryptic digestion a precipitate was formed which showed properties characteristic of amyloid, such as staining with Congo red and green birefringence in polarized light. High-performance liquid chromatography was applied to separate these peptides. The precipitate consists of two peptides which coincide with position 19-45 of the variable and 129-140 of the constant part, respectively. Possible implications of this finding are discussed in the context of amyloid formation after limited proteolytic digestion.

Structural studies of a carbohydrate-containing immunoglobulin-lambda-light-chain amyloid-fibril protein (AL) of variable subgroup III

The amino acid sequence of the variable region of a carbohydrate-containing amyloid-fibril protein MOL of immunoglobulin-light-chain type (AL) was elucidated. The sequence determination involved cleaving the protein with CNBr, BNPS-skatole, thermolysin and trypsin. The sequenced protein consisted of about 130 amino acid residues; however, gel-filtration and N-terminal analysis studies revealed AL proteins ranging in Mr from about 10,000 to 25,000. The oligosaccharide chain was found to be bound in the hypervariable region. By sequence homology to other lambda chains the AL protein MOL was shown to be of the V lambda III subgroup.