Mechanism Of Amyloid Fibril Formation Research Articles

Prediction of Amyloidogenic and Disordered Regions in Protein Chains

The determination of factors that influence protein conformational changes is very important for the identification of potentially amyloidogenic and disordered regions in polypeptide chains. In our work we introduce a new parameter, mean packing density, to detect both amyloidogenic and disordered regions in a protein sequence. It has been shown that regions with strong expected packing density are responsible for amyloid formation. Our predictions are consistent with known disease-related amyloidogenic regions for eight of 12 amyloid-forming proteins and peptides in which the positions of amyloidogenic regions have been revealed experimentally. Our findings support the concept that the mechanism of amyloid fibril formation is similar for different peptides and proteins. Moreover, we have demonstrated that regions with weak expected packing density are responsible for the appearance of disordered regions. Our method has been tested on datasets of globular proteins and long disordered protein segments, and it shows improved performance over other widely used methods. Thus, we demonstrate that the expected packing density is a useful value with which one can predict both intrinsically disordered and amyloidogenic regions of a protein based on sequence alone. Our results are important for understanding the structural characteristics of protein folding and misfolding.

Identification of the Region Responsible for Fibril Formation in the CAD Domain of Caspase-Activated DNase

Caspase-activated DNase (CAD) has a compact domain at its N-terminus (CAD domain, 87 amino acid residues), which comprises one alpha-helix and five beta-strands forming a single sheet. The CAD domain of CAD (CAD-CD) forms amyloid fibrils containing alpha-helix at low pH in the presence of salt. To obtain insights into the mechanism of amyloid fibril formation, we identified the peptide region essential for fibril formation of CAD-CD and the region responsible for the salt requirement. We searched for these regions by constructing a series of deletion and point mutants of CAD-CD. Fibril formation by these CAD-CD mutants was examined by fluorescence analysis of thioflavin T and transmission electron microscopy. C-Terminal deletion and point mutation studies revealed that an aromatic residue near the C-terminus (Trp81) is critical for fibril formation. In addition, the main chain conformation of the beta5 strand, which forms a hydrophobic core with Trp81, was found to be important for the fibril formation by CAD-CD. The N-terminal 30 amino acid region containing two beta-strands was not essential for fibril formation. Rather, the N-terminal region was found to be responsible for the requirement of salt for fibril formation.

Core and Heterogeneity of β 2-Microglobulin Amyloid Fibrils as Revealed by H/D Exchange

Dialysis-related amyloidosis, which occurs in the patients receiving a long-term hemodialysis with high frequency, accompanies the deposition of amyloid fibrils composed of β 2-microglobulin (β2-m). In vitro, β2-m forms two kinds of fibrous structures at acidic pH. One is a rigid “mature fibril”, and the other is a flexible thin filament often called an “immature fibril”. In addition, a 22-residue peptide (K3 peptide) corresponding to Ser20 to Lys41 of intact β2-m forms rigid amyloid-like fibrils similar to mature fibrils. We compared the core of these three fibrils at single-residue resolution using a recently developed hydrogen/deuterium (H/D) exchange method with the dissolution of fibrils by dimethylsulfoxide (DMSO). The exchange time-course of these fibrils showed large deviations from a single exponential curve showing that, because of the supramolecular structures, the same residue exists in different environments from molecule to molecule, even in a single fibril. The exchange profiles revealed that the core of the immature fibril is restricted to a narrow region compared to that of the mature fibril. In contrast, all residues were protected from exchange in the K3 fibril, indicating that a whole region of the peptide is engaged in the β-sheet network. These results suggest the mechanism of amyloid fibril formation, in which the core β-sheet formed by a minimal sequence propagates to form a rigid and extensive β-sheet network.

Amyloid fibrils from the viewpoint of protein folding.

In amyloid related diseases, proteins form fibrillar aggregates with highly ordered beta-sheet structure regardless of their native conformations. Formation of such amyloid fibrils can be reproducible in vitro using isolated proteins/peptides, suggesting that amyloid fibril formation takes place as a result of protein conformational change. In vitro studies revealed that perturbation of the native structure is important for the fibril formation, and it is suggested that the mechanisms of amyloid fibril formation share the mechanisms of protein folding. In particular, amyloid fibril formation is similar to one of the common features of proteins, i.e. amorphous aggregation upon partial unfolding, which is likely driven by hydrophobic interactions through exposed protein interior. However, these molecular associations are distinct phenomena, and identifying factors that lead to amyloid fibril formation would precede our understanding of the mechanisms of amyloid fibrillization. The necessity of understanding the nature of protein denatured states is also suggested.

Structure and Formation of Amyloid Fibrils of .BETA.2-Microglobulin

Amyloid fibril formation is a phenomenon common to many proteins and peptides. Clarifying the mechanism of amyloid fibril formation is essential not only for understanding the pathogenesis of amyloidosis but also for improving our understanding of the mechanism of protein folding. Dialysis-related amyloidosis is a common and serious complication among patients on long-term hemodialysis, in which β2-microglobulin forms amyloid fibrils. We studied the core of fibrils at single-residue resolution using recently developed H/D exchange method with the dissolution of fibrils by dimethylsulfoxide. The results suggest the mechanism of amyloid fibril formation, in which the core β-sheet formed by a minimal sequence propagates to form a rigid and extensive β-sheet network.

Amyloid Fibril Formation in the Context of Full-length Protein: EFFECTS OF PROLINE MUTATIONS ON THE AMYLOID FIBRIL FORMATION OF β2-MICROGLOBULIN

Beta2-microglobulin (beta2-m), a typical immunoglobulin domain made of seven beta-strands, is a major component of amyloid fibrils formed in dialysis-related amyloidosis. To understand the mechanism of amyloid fibril formation in the context of full-length protein, we prepared various mutants in which proline (Pro) was introduced to each of the seven beta-strands of beta2-m. The mutations affected the amyloidogenic potential of beta2-m to various degrees. In particular, the L23P, H51P, and V82P mutations significantly retarded fibril extension at pH 2.5. Among these, only L23P is included in the known "minimal" peptide sequence, which can form amyloid fibrils when isolated as a short peptide. This indicates that the residues in regions other than the minimal sequence, such as H51P and V82P, determine the amyloidogenic potential in the full-length protein. To further clarify the mutational effects, we measured their stability against guanidine hydrochloride of the native state at pH 8.0 and the amyloid fibrils at pH 2.5. The amyloidogenicity of mutants showed a significant correlation with the stability of the amyloid fibrils, and little correlation was observed with that of the native state. It has been proposed that the stability of the native state and the unfolding rate to the amyloidogenic precursor as well as the conformational preference of the denatured state determine the amyloidogenicity of the proteins. The present results reveal that, in addition, stability of the amyloid fibrils is a key factor determining the amyloidogenic potential of the proteins.

Role of the C-terminal 28 residues of beta2-microglobulin in amyloid fibril formation.

Beta2microglobulin (beta2m) is the major protein component of the fibrillar amyloid deposits isolated from patients diagnosed with dialysis-related amyloidosis (DRA). While investigating the molecular mechanism of amyloid fibril formation by beta2m, we found that the beta2m C-terminal peptide of 28 residues (cbeta2m) itself forms amyloid fibrils. When viewed by electron microscopy, cbeta2m aggregates appear as elongated unbranched fibers, the morphology typical for amyloids. Cbeta2m fibers stain with Congo red and show apple-green birefringence in polarized light, characteristic of amyloids. The observation that the beta2m C-terminal fragment readily forms amyloid fibrils implies that beta2m amyloid fibril formation proceeds via interactions of amyloid forming segments, which become exposed when the beta2m subunit is partially unfolded.

Direct Observation of Amyloid Fibril Growth Monitored by Thioflavin T Fluorescence

Real-time monitoring of fibril growth is essential to clarify the mechanism of amyloid fibril formation. Thioflavin T (ThT) is a reagent known to become strongly fluorescent upon binding to amyloid fibrils. Here, we show that, by monitoring ThT fluorescence with total internal reflection fluorescence microscopy (TIRFM), amyloid fibrils of beta2-microgobulin (beta2-m) can be visualized without requiring covalent fluorescence labeling. One of the advantages of TIRFM would be that we selectively monitor fibrils lying along the slide glass, so that we can obtain the exact length of fibrils. This method was used to follow the kinetics of seed-dependent beta2-m fibril extension. The extension was unidirectional with various rates, suggesting the heterogeneity of the amyloid structures. Since ThT binding is common to all amyloid fibrils, the present method will have general applicability for the analysis of amyloid fibrils. We confirmed this with the octapeptide corresponding to the C terminus derived from human medin and the Alzheimer's amyloid beta-peptide.

A model for amyloid fibril formation in immunoglobulin light chains based on comparison of amyloidogenic and benign proteins and specific antibody binding

In an attempt to understand the mechanism of amyloid fibril formation in light chain amyloidosis, the properties of amyloidogenic (SMA) and benign (LEN) immunoglobulin light chain variable domains (VL) were compared. The conformations of LEN and SMA were measured using secondary and tertiary structural probes over the pH range from 2 and 8. At all pH values, LEN was more stable than SMA. The CD spectra of LEN at pH 2 were comparable to those of SMA atpH 7.5, indicating that the low pH conformation of LEN closely resembles that of SMA at physiological pH. At low pH, a relatively unfolded intermediate conformation is populated for SMA and rapidly leads to amyloid fibrils. The luck of such an intermediate with LEN, is attributed to sequence differences and accounts for the lack of LEN fibrils in the absence of agitation. A κIV-specific monoclonal antibody that recognizes the N-terminal of SMA caused unraveling of the fibrils to the protofilaments and was observed to bind to one end of SMA protofilaments by atomic force microscopy. The antibody result indicates that each protofilament is asymmetric with different ends. A model for the formation of fibrils by SMA is proposed.

An Insight into the pathway of the amyloid fibril formation of hen egg white lysozyme obtained from a small-angle X-ray and neutron scattering study.

It is known that hen egg white lysozyme (HEWL) forms amyloid fibrils. Since HEWL is one of the proteins that have been studied most extensively and is closely related to human lysozyme, the variants of which form the amyloid fibrils that are related to hereditary systemic amyloidosis, this protein is an ideal model to study the mechanism of amyloid fibril formation. In order to gain an insight into the mechanism of amyloid fibril formation, systematic and detailed studies to detect and characterize various structural states of HEWL were conducted. Since HEWL forms amyloid fibrils in highly concentrated ethanol solutions, solutions of various concentrations of HEWL in various concentrations of ethanol were prepared, and the structures of HEWL in these solutions were investigated by small-angle X-ray and neutron scattering. It was shown that the structural states of HEWL were distinguished as the monomer state, the state of the dimer formation, the state of the protofilament formation, the protofilament state, and the state towards the formation of amyloid fibrils. A phase diagram of these structural states was obtained as a function of protein, water and ethanol concentrations. It was found that under the monomer state the structural changes of HEWL were not gross changes in shape but local conformational changes, and the dimers, formed by the association at the end of the long axis of HEWL, had an elongated shape. Circular dichroism measurements showed that the large changes in the secondary structures of HEWL occurred during dimer formation. The protofilaments were formed by stacking of the dimers with their long axis (nearly) perpendicular to and rotated around the protofilament axis to form a helical structure. These protofilaments were characterized by their radius of gyration of the cross-section of 2.4nm and the mass per unit length of 16,000(+/-2300)Da/nm. It was shown that the changes of the structural states towards the amyloid fibril formation occurred via lateral association of the protofilaments. A pathway of the amyloid fibril formation of HEWL was proposed from these results.

Elongation in a beta-structure promotes amyloid-like fibril formation of human lysozyme.

To understand the mechanism of amyloid fibril formation of a protein, we examined wild-type and three mutant human lysozymes containing both amyloidogenic and non-amyloidogenic proteins: I56T (amyloidogenic); EAEA, which has four additional residues (Glu-Ala-Glu-Ala-) at the N-terminus located on a beta-structure; and EAEA-I56T, which is an I56T mutant of EAEA. All formed amyloid-like fibrils through an in the increase contents of alpha-helix with increasing concentration of ethanol. The order of propensity for amyloid-like fibril formation in highly concentrated ethanol solution is EAEA-I56T > EAEA > I56T > wild-type. This order is almost the reverse of the order of conformational stability of these proteins, wild-type > EAEA > I56T > EAEA-I56T. The important views in this work are as follows. (i) Artificially modified proteins formed amyloid fibrils in vitro. This means that amyloid formation is a generic property of polypeptide chains. (ii) The amyloidogenic mutation Ile56 to Thr caused the destabilization and promoted fibril formation in the wild-type and EAEA human lysozymes, indicating that instability facilitates amyloid formation. (iii) The mutant protein EAEA human lysozyme had higher propensity for fibril formation than the amyloidogenic mutant protein, indicating that amyloid formation is controlled not only by stability but also by other factors. In this case, appending polypeptide chains to a beta-structure accelerated amyloid formation.

Investigation of a Peptide Responsible for Amyloid Fibril Formation of β2-Microglobulin byAchromobacter Protease I

To obtain insight into the mechanism of amyloid fibril formation from beta(2)-microglobulin (beta2-m), we prepared a series of peptide fragments using a lysine-specific protease from Achromobacter lyticus and examined their ability to form amyloid fibrils at pH 2.5. Among the nine peptides prepared by the digestion, the peptide Ser(20)-Lys(41) (K3) spontaneously formed amyloid fibrils, confirmed by thioflavin T binding and electron microscopy. The fibrils composed of K3 peptide induced fibril formation of intact beta2-m with a lag phase, distinct from the extension reaction without a lag phase observed for intact beta2-m seeds. Fibril formation of K3 peptide with intact beta2-m seeds also exhibited a lag phase. On the other hand, the extension reaction of K3 peptide with the K3 seeds occurred without a lag phase. At neutral pH, the fibrils composed of either intact beta2-m or K3 peptide spontaneously depolymerized. Intriguingly, the depolymerization of K3 fibrils was faster than that of intact beta2-m fibrils. These results indicated that, although K3 peptide can form fibrils by itself more readily than intact beta2-m, the K3 fibrils are less stable than the intact beta2-m fibrils, suggesting a close relation between the free energy barrier of amyloid fibril formation and its stability.

Extension of Aβ2M amyloid fibrils with recombinant human β2-microglobulin

In order to elucidate the pathogenesis ofAβ2M amyloidosis, we established an experimental system to study the mechanism of amyloid fibril formation or degradation in vitro. We compared the kinetics of Aβ2M amyloid fibril (fAβ2M) extension with native β2microglobulin (n-β2M) purified from the urine of a patient suffering from renal insufficiency, with that with recombinant β2M (r-β2M) in vitro. n-β2M and r-β2M were incubated with fβ32Mpurifiedfrom synovial tissues excised from Aβ2M amyloidosis patients. The fA β2M extension reaction could be explained by a first-order kinetic model in both β2Ms. The extension reaction was greatly dependent on the pH of the reaction mixture and maximum around pH 2.5-3.0 in both p2Ms. ThefAβ2M extended with both p2Ms assumed the similar helical filament structure, although the fibrils extended with r-β2M were slightly wider than those extended with n-β2M and the former fibrils assumed a helical structure more clearly as compared to the latter. In order to obtain pure, unmodifiedfAβ2M, we next extendedfA β2M repeatedly by the algorithmic protocol with r-β2M. As the generation of the extended fibrils proceeded, the initial rate of the extension reaction increased. The ultrastructure of fibrils was completely preserved throughout the repeated extension steps. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunoblotting revealed that f A P2M extended repeatedly with r-β2Mwere composed solely ofr-β2M. The use of these r-β2M and fAβ2M will be advantageous to assess the effects of several amyloid-associated molecules in the formation or degradation offAβ2M in vitro.

The stability and folding process of amyloidogenic mutant human lysozymes

Amyloid deposits are frequently formed by mutant proteins that have a lower stability than the wild-type proteins. Some reports, however, have shown that mutant-induced thermodynamic destabilization is not always a general mechanism of amyloid formation. To obtain a better understanding of the mechanism of amyloid fibril formation, we show in this study that equilibrium and kinetic refolding-unfolding reaction experiments with two amyloidogenic mutant human lysozymes (I56T and D67H) yield folding pathways that can be drawn as Gibbs energy diagrams. The equilibrium stabilities between the native and denatured states of both mutant proteins were decreased, but the degrees of instability were different. The Gibbs energy diagrams of the folding process reveal that the Gibbs energy change between the native and folding intermediate states was similar for both proteins, and also that the activation Gibbs energy change from the native state to the transition state decreased. Our results confirm that the tendency to favor the intermediate of denaturation facilitates amyloid formation by the mutant human lysozymes more than equilibrium destabilization between the native and completely denatured states does.

The process of amyloid-like fibril formation by methionine aminopeptidase from a hyperthermophile, Pyrococcus furiosus.

Amyloid is associated with serious diseases including Alzheimer's disease and senile-systemic amyloidosis due to misfolded proteins. In the course of study of the denaturation process of methionine aminopeptidase (MAP) from the hyperthermophile P. furiosus, we found that MAP forms amyloid-like fibrils, and we then investigated the mechanism of amyloid fibril formation. The kinetic experiments on denaturation monitored by CD at 222 nm indicated that MAP in the presence of 3.37 M GuHCl at pH 3.31 changed to a conformation containing a considerable content of beta-sheet structure after the destruction of the alpha-helical structure. MAP in this beta-rich conformation was highly associated, and its stability was remarkably high: the midpoint of the GuHCl denaturation curve was 4.82 M at pH 3.0, and a thermal transition was not observed up to 125 degrees C by calorimetry. The amyloid-like fibril formation of MAP was confirmed by Congo red staining with a typical peak at 542 nm in the difference spectrum, showing a cross-beta X-ray diffraction pattern with a clear sharp reflection at 4.7 A and a characteristic unbranched fibrillar appearance with a length of about 1000 A and a diameter of about 70 A in the electron micrographs. Present results indicate that the amyloid-like form of MAP appears just after the protein is almost completely denatured, and even highly stable proteins can also form amyloid-like conformation under conditions where the denatured state of the protein is abundantly populated.

A peptide from the adenovirus fiber shaft forms amyloid-type fibrils

The fiber protein of adenovirus consists of a C-terminal globular head, a shaft and a short N-terminal tail. The crystal structure of a stable domain comprising the head plus a part of the shaft of human adenovirus type 2 fiber has recently been solved at 2.4 Å resolution [van Raaij et al. (1999) Nature 401, 935–938]. A peptide corresponding to the portion of the shaft immediately adjacent to the head (residues 355–396) has been synthesized chemically. The peptide failed to assemble correctly and instead formed amyloid-type fibrils as assessed by electron microscopy, Congo red binding and X-ray diffraction. Peptides corresponding to the fiber shaft could provide a model system to study mechanisms of amyloid fibril formation.

20] Kinetic analysis of amyloid fibril formation

A nucleation-dependent polymerization model has been proposed to explain the mechanisms of amyloid fibril formation in vitro. This model consists of two phases—the nucleation and extension phases. Nucleus formation requires a series of association steps of monomers that are thermodynamically unfavorable, representing the rate-limiting step in amyloid fibril formation. Once the nucleus ( n -mer) has been formed, the further addition of monomers becomes thermodynamically favorable, resulting in a rapid extension of amyloid fibrils. This chapter developes a first-order kinetic model of amyloid fibril extension in vitro and confirmed that the extension of amyloid fibrils proceeds via the consecutive association of monomeric precursor proteins onto the ends of existing fibrils. A characteristic sigmoidal time-course curve of amyloid fibril formation from monomeric precursor proteins at a physiological pH is widely believed to represent the essence of a nucleation-dependent polymerization model—that is, an initial lag phase represents the thermodynamically unfavorable nucleus formation. However, no convincing kinetic models to explain the sigmoidality of the curve have been reported. This chapter describes the paradigm to analyze the kinetic aspect of amyloid fibril formation in vitro. During the investigation of murine senile amyloidosis observed in the senescence-accelerated mouse (SAM), it develops a novel fluorometric method to determine amyloid fibrils in vitro based on the unique characteristics of thioflavin T (ThT). In recent years, this method has been applied to the analysis of several human amyloidoses, including gelsolin-derived amyloidosis, dialysis-related amyloidosis, and Alzheimer's β -amyloidosis. With this fluorometric method, this chapter successfully measures the polymerization velocity of three types of amyloid fibrils—that is, murine senile amyloid fibrils (fAApoAII), Alzheimer's β -amyloid fibrils (fA β ), and dialysis-related amyloid fibrils (fA β 2 -m), and performs kinetic analysis of amyloid fibril polymerization in vitro.

Partial denaturation of transthyretin is sufficient for amyloid fibril formation in vitro.

Amyloid diseases are caused by the self-assembly of a given protein into an insoluble cross-beta-sheet quaternary structural form which is pathogenic. An understanding of the biochemical mechanism of amyloid fibril formation should prove useful in understanding amyloid disease. Toward this end, a procedure for the conversion of the amyloidogenic protein transthyretin into amyloid fibrils under conditions which mimic the acidic environment of a lysosome has been developed. Association of a structured transthyretin denaturation intermediate is sufficient for amyloid fibril formation in vitro. The rate of fibril formation is pH dependent with significant rates being observed at pHs accessible within the lysosome (3.6-4.8). Far-UV CD spectroscopic studies suggest that transthyretin retains its secondary structural features at pHs where fibrils are formed. Near-UV CD studies demonstrate that transthyretin has retained the majority of its tertiary structure during fibril formation as well. Near-UV CD analysis in combination with glutaraldehyde cross-linking studies suggests that a pH-mediated tetramer to monomer transition is operative in the pH range where fibril formation occurs. The rate of fibril formation decreases markedly at pHs below pH 3.6, consistent with denaturation to a monomeric TTR intermediate which has lost its native tertiary structure and capability to form fibrils. It is difficult to specify with certainty which quaternary structural form of transthyretin is the amyloidogenic intermediate at this time. These difficulties arise because the maximal rate of fibril formation occurs at pH 3.6 where tetramer, traces of dimer, and significant amounts of monomer are observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Amyloidosis

The clinical amyloidosis syndromes are a heterogeneous group of disorders characterised by abnormal extracellular accumulation of autologous protein material. Amyloid deposits are largely composed of insoluble protein fibrils which are intimately associated with sulphated glycosaminoglycan residues. Amyloid P component (AP) is a minor but almost universal constituent of the deposits and is derived from the normal circulating glycoprotein serum amyloid P component (SAP), a member of the pentraxin family of plasma proteins. The current classification of amyloidosis is based on the chemical nature of the fibril protein subunits. Systemic amyloidosis is well known as a relatively rare but important cause of serious morbidity, and vital organ involvement is usually fatal. In recent years it has become increasingly recognised that amyloid deposition in a variety of sites is a universal feature of ageing, and in particular that amyloid in the cerebral blood vessels and within the brain itself is an integral part of the pathology of Alzheimer's disease. Also recently, a new form of amyloid has emerged, confined to patients who have received long term haemodialysis for end stage renal failure, in whom β 2-microglobulin ( β 2M) is laid down as amyloid fibrils predominantly in periarticular and bony tissues. Considerable progress in knowledge of the composition, molecular structure and properties of many different constituents of amyloid has been made in the past 30 years. However, the precise mechanisms of amyloid fibril formation, deposition and persistence are not known and no generally effective therapy yet exists which can arrest amyloid deposition or promote its resolution. A major reason for our ignorance of the natural history of amyloidosis is that it is an exclusively histological diagnosis, at the time of which most patients with systemic disease have extensive amyloid deposits throughout many organs and a very poor prognosis. Some optimism has been generated from recent work suggesting that amyloid fibrils are not inherently non-biodegradable and that the use of radiolabelled SAP may permit non-invasive sensitive, scintigraphic imaging of amyloid deposits in vivo.

Pathological Society of Great Britain and Ireland. 154th meeting, 7-9 January 1987. Synopses of papers.

The transformation of serum proteins into Congo red-sensitive fibrillar material is requisite for the onset and progression of amyloid disease. All the mechanisms which lead to the disease itself have not been elucidated, but our knowledge has increased significantly. It is apparent that in all types of amyloid fibrils, three common features are displayed by the major protein constituents. These are that the fibril protein has a serum precursor, a high degree of anti-parallel beta-sheet conformation and a distinctive ultrastructure on electron microscopy. In the AL and AA forms of amyloidosis, the putative precursors appear to undergo limited degradation to form the protein component of amyloid fibrils. It has been suggested that there may be certain primary structural characteristics inherent in precursor molecules which make them amyloidogenic, thus predisposing them to amyloid fibril formation. This would include certain subtypes of immunoglobulin light chains, possibly kappa I and lambda VI, in the AL type of amyloidosis and one of the polymorphic SAA species, SAA2, which has been identified as the predominating isotype found in AA amyloid fibrils. In AH amyloidosis, the mechanism of amyloid fibril formation appears to be simply a concentration phenomenon where elevated concentrations of B2-M are not handled normally and amyloid deposition is the result. Amyloidogenesis in the hereditary form of systemic amyloidosis may involve other factors in addition to the presence of a variant precursor prealbumin as indicated by the delayed onset of the disease. It is evident that the elucidation of the mechanism(s) which governs the onset and progression of the amyloidoses will allow future regulation and treatment of these all too often complex disorders.