Structural relationship of kappa-type light chains with AL amyloidosis: multiple deletions found in a VkappaIV protein

Amyloid formation in light chain amyloidosis

Light chain amyloidosis is one of the unique examples within amyloid diseases where the amyloidogenic precursor is a protein that escapes the quality control machinery and is secreted from the cells to be circulated in the bloodstream. The immunoglobulin light chains are produced by an abnormally proliferative monoclonal population of plasma cells that under normal conditions produce immunoglobulin molecules such as IgG, IgM or IgA. Once the light chains are in circulation, the proteins misfold and deposit as amyloid fibrils in numerous tissues and organs, causing organ failure and death. While there is a correlation between the thermodynamic stability of the protein and the kinetics of amyloid formation, we have recently found that this correlation applies within a thermodynamic range, and it is only a helpful correlation when comparing mutants from the same protein. Light chain amyloidosis poses unique challenges because each patient has a unique protein sequence as a result of the selection of a germline gene and the incorporation of somatic mutations. The exact location of the misfolding process is unknown as well as the full characterization of all of the toxic species populated during the amyloid formation process in light chain amyloidosis.

Aggregates, crystals, gels, and amyloids: intracellular and extracellular phenotypes at the crossroads of immunoglobulin physicochemical property and cell physiology

Recombinant immunoglobulins comprise an important class of human therapeutics. Although specific immunoglobulins can be purposefully raised against desired antigen targets by various methods, identifying an immunoglobulin clone that simultaneously possesses potent therapeutic activities and desirable manufacturing-related attributes often turns out to be challenging. The variable domains of individual immunoglobulins primarily define the unique antigen specificities and binding affinities inherent to each clone. The primary sequence of the variable domains also specifies the unique physicochemical properties that modulate various aspects of individual immunoglobulin life cycle, starting from the biosynthetic steps in the endoplasmic reticulum, secretory pathway trafficking, secretion, and the fate in the extracellular space and in the endosome-lysosome system. Because of the diverse repertoire of immunoglobulin physicochemical properties, some immunoglobulin clones' intrinsic properties may manifest as intriguing cellular phenotypes, unusual solution behaviors, and serious pathologic outcomes that are of scientific and clinical importance. To gain renewed insights into identifying manufacturable therapeutic antibodies, this paper catalogs important intracellular and extracellular phenotypes induced by various subsets of immunoglobulin clones occupying different niches of diverse physicochemical repertoire space. Both intrinsic and extrinsic factors that make certain immunoglobulin clones desirable or undesirable for large-scale manufacturing and therapeutic use are summarized.

A single mutation promotes amyloidogenicity through a highly promiscuous dimer interface

Light chain amyloidosis is a devastating protein misfolding disease characterized by the accumulation of amyloid fibrils that causes tissue damage and organ failure. These fibrils are composed of monoclonal light chain protein secreted from an abnormal proliferation of bone marrow plasma cells. We previously reported that amyloidogenic light chain protein AL-09 adopts an altered dimer while its germline protein (kappaI O18/O8) forms a canonical dimer observed in other light chain crystal structures. In solution, conformational heterogeneity obscures all NMR signals at the AL-09 and kappaI O18/O8 dimer interfaces, so we solved the nuclear magnetic resonance structure of two related mutants. AL-09 H87Y adopts the normal dimer interface, but the kappaI Y87H solution structure presents an altered interface rotated 180 degrees relative to the canonical dimer interface and 90 degrees from the AL-09 arrangement. Our results suggest that promiscuity in the light chain dimer interface may promote new intermolecular contacts that may contribute to amyloid fibril structure.

Light chain amyloidosis - current findings and future prospects

Systemic light chain amyloidosis (AL) is one of several protein misfolding diseases and is characterized by extracellular deposition of immunoglobulin light chains in the form of amyloid fibrils [1]. Immunoglobulin (Ig) proteins consist of two light chains (LCs) and two heavy chains (HCs) that ordinarily form a heterotetramer which is secreted by a plasma cell. In AL, however, a monoclonal plasma cell population produces an abundance of a pathogenic LC protein. In this case, not all of the LCs pair with the HCs, and free LCs are secreted into circulation. The LC-HC dimer is very stable, and losing this interaction may result in an unstable LC protein [2]. Additionally, somatic mutations are thought to cause amyloidogenic proteins to be less stable compared to non-amyloidogenic proteins [3-5], leading to protein misfolding and amyloid fibril formation. The amyloid fibrils cause tissue damage and cell death, leading to patient death within 12-18 months if left untreated [6]. Current therapies are harsh and not curative, including chemotherapy and autologous stem cell transplants. Studies of protein pathogenesis and fibril formation mechanisms may lead to better therapies with an improved outlook for patient survival. Much has been done to determine the molecular factors that make a particular LC protein amyloidogenic and to elucidate the mechanism of amyloid fibril formation. Anthony Fink's work, particularly with discerning the role of intermediates in the fibril formation pathway, has made a remarkable impact in the field of amyloidosis research. This review provides a general overview of the current state of AL research and also attempts to capture the most recent ideas and knowledge generated from the Fink laboratory.

Structural alterations within native amyloidogenic immunoglobulin light chains

Amyloid diseases are characterized by the misfolding of a precursor protein that leads to amyloid fibril formation. Despite the fact that there are different precursors, some commonalities in the misfolding mechanism are thought to exist. In light chain amyloidosis (AL), the immunoglobulin light chain forms amyloid fibrils that deposit in the extracellular space of vital organs. AL proteins are thermodynamically destabilized compared to non-amyloidogenic proteins and some studies have linked this instability to increased fibril formation rates. Here we present the crystal structures of two highly homologous AL proteins, AL-12 and AL-103. This structural study shows that these proteins retain the canonical germ line dimer interface. We highlight important structural alterations in two loops flanking the dimer interface and correlate these results with the somatic mutations present in AL-12 and AL-103. We suggest that these alterations are informative structural features that are likely contributing to protein instability that leads to conformational changes involved in the initial events of amyloid formation.

Altered dimer interface decreases stability in an amyloidogenic protein

Amyloidoses are devastating and currently incurable diseases in which the process of amyloid formation causes fatal cellular and organ damage. The molecular mechanisms underlying amyloidoses are not well known. In this study, we address the structural basis of immunoglobulin light chain amyloidosis, which results from deposition of light chains produced by clonal plasma cells. We compare light chain amyloidosis protein AL-09 to its wild-type counterpart, the kappaI O18/O8 light chain germline. Crystallographic studies indicate that both proteins form dimers. However, AL-09 has an altered dimer interface that is rotated 90 degrees from the kappaI O18/O8 dimer interface. The three non-conservative mutations in AL-09 are located within the dimer interface, consistent with their role in the decreased stability of this amyloidogenic protein. Moreover, AL-09 forms amyloid fibrils more quickly than kappaI O18/O8 in vitro. These results support the notion that the increased stability of the monomer and delayed fibril formation, together with a properly formed dimer, may be protective against amyloidogenesis. This could open a new direction into rational drug design for amyloidogenic proteins.

Deposition-associated diseases related with a monoclonal compound

Up to 3% of adults over 50 years of age show a monoclonal peak values in blood or urine. Findings and prognosis will be distinct in view of the nature of this factor. In B-cell neoplasias (multiple myeloma, Waldeström macroglobulinaemia, chronic myeloid leukaemia and non-Hodgkin lymphoma) the clinical pattern is dominated by the systemic effects produced by the expansion of the malign clone; the monoclonal protein may result in hyperviscosity syndrome or renal damage. On the other hand, there are other less frequent processes called diseases associated to monoclonal components, where the main clinical manifestations and prognosis depend of the biological effects of the monoclonal protein. With reference to this last group, which is the objective of this revision, no bone lesions, anaemia or a greater tendency to infections usually occur when compared with the first group. Even so, there are some cases of interposition between both groups: for instance, type IgM immunoglobulin present in Waldeström macroglobulinaemia may have cold agglutinin activity, and in the case of multiple myeloma, the clone may secrete amyloidogenic light chains.

Where disease pathogenesis meets protein formulation: Renal deposition of immunoglobulin aggregates

Aggregation is one of the important issues encountered during the development of immunoglobulin-based drugs. The aim of the current review is to discuss the causes and consequences of immunoglobulin aggregation as well as the relevance of immunoglobulin aggregation to disease pathogenesis. Extracellular deposition of immunoglobulins, either monoclonal light chains or intact polyclonal antibodies, induces renal failure in various nephropathies. The aggregates can present fibrillar or amorphous structures. In this review, factors known to influence protein aggregation, such as the primary structure of the protein, local environment and glycosylation are assessed, as well as the subsequent altered clearance, fibril formation and toxicity. The role of the protein local environment is emphasized. Even if the local environment causes only minor perturbations in the protein structure, these perturbations might be sufficient to trigger aggregate formation. This fact underlines the importance of choosing appropriate formulations for protein drugs. If the formulation provides a slightly destabilizing environment to the protein, the long-term stability of the drug may be compromised by aggregate formation.

Immunoglobulin kappa light chain and its amyloidogenic mutants: A molecular dynamics study

AL amyloidosis and LCDD are pathological conditions caused by extracellural deposition of monoclonal Ig light chain variable domains. In the former case, deposits have a form of amyloid fibrils, in the latter, amorphous aggregates. 1REI kappa light chain variable domain and its two point mutants, R61N and D82I, were chosen for the analysis in this work. Wild 1REI does not create deposits in vitro, while R61N aggregates as amyloid fibrils and D82I creates amorphous aggregates. Both mutated residues create a conserved salt bridge; thus, substitution of any of them should decrease V(L) domain stability. For these three proteins, 5 ns MD simulations were conducted in temperatures of 300 K and 400 K, with protonated and unprotonated acidic residues, mimicking acidic and neutral experimental pH conditions (3 sets: N300, N400, and A400). The analysis of trajectories focused on characterization of changes in conformational behavior and stability of Ig kappa light chain variable domain caused by single aminoacid substitutions that were experimentally proved to enhance aggregation propensity, both in the form of amyloid and amorphous aggregates. Residue D82 turns out to be involved not only in R61-D82 but also in K45-D82 interaction, which was not observed in the X-ray structure, but frequently populated simulations of 1REI. The substitution D82I excludes both interactions, resulting in substantial destabilization (i.e., easier aggregation). Examination of behavior of edge regions of V(L) beta-sandwich reveals significant alterations in D82I mutant compared to wild 1REI, while relatively small changes occur in R61N. This suggests that mild and slow destabilization is the reason of the conversion of V(L) to partially folded amyloidogenic intermediate structure.

Immunoglobulin light chain amyloidosis and the kidney

Immunoglobulin light chain amyloidosis and the kidney. Amyloidosis (AL) is a common cause of nephrotic syndrome in nondiabetic, nonhypertensive adults. All adult patients with nephrotic syndrome should have immunofixation of serum and urine as a screen. The finding of a monoclonal protein, particularly of lambda type, should lead to a subcutaneous fat aspirate or bone marrow biopsy to search for amyloid deposits. When the result of either test is positive, a kidney biopsy is unnecessary. The prognosis of patients who have renal amyloidosis depends on the concentration of serum creatinine at presentation and whether an echocardiographic evaluation demonstrates infiltrative cardiomyopathy. Most therapies are directed against the plasma cell dyscrasia present in all patients with AL and can include melphalan and prednisone, high-dose dexamethasone, and, most recently, peripheral blood stem cell transplantation.