Kidney dialysis-associated amyloidosis: a molecular role for copper in fiber formation

Morgan, Charles G.; Gelfand, Michael; Atreya, Chloé E.; Miranker, Andrew D.

doi:10.1006/jmbi.2001.4661

Cited by 161 publications

(192 citation statements)

References 31 publications

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“…Importantly, the peak area of the electropherogram corresponding to the I 2 species appears reduced when a ␤ 2 -m sample is analyzed after preincubation with natural fibrils, indicating preferential interaction of the fibrils with I 2 . 2 There seem to be a general consensus that ␤ 2 -m is relatively stable in vitro at pH values close to those found in the plasma and in the extracellular spaces and that in vivo particular events are required to destabilize the native fold of ␤ 2 -m and therefore initiate the aggregation process (9,10,19,21). Our results are in agreement with these findings, since fibril formation does not occur in the absence of preformed fibrils at pH 7.4.…”

Section: Discussionmentioning

confidence: 99%

“…Various hypotheses have been put forward as possible mechanisms nucleating aggregation in vivo. These include destabilization of a fraction of ␤ 2 -m molecules by proteolytic cleavage of the six N-terminal residues (9), uptake into lysosomes of macrophages with consequent exposure of the protein to acidic pH values at which aggregation is more favored (10,19), and destabilization by Cu 2ϩ ions possibly released by hemodialyzed membranes (21).…”

Section: Discussionmentioning

confidence: 99%

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A Partially Structured Species of β2-Microglobulin Is Significantly Populated under Physiological Conditions and Involved in Fibrillogenesis

Chiti

Lorenzi

Grossi

et al. 2001

Journal of Biological Chemistry

144

188

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The folding of ␤ 2 -microglobulin (␤ 2 -m), the protein forming amyloid deposits in dialysis-related amyloidosis, involves formation of a partially folded conformation named I 2 , which slowly converts into the native fold, N. Here we show that the partially folded species I 2 can be separated from N by capillary electrophoresis. Data obtained with this technique and analysis of kinetic data obtained with intrinsic fluorescence indicate that the I 2 conformation is populated to ϳ14 ؎ 8% at equilibrium under conditions of pH and temperature close to physiological. In the presence of fibrils extracted from patients, the I 2 conformer has a 5-fold higher propensity to aggregate than N, as indicated by the thioflavine T test and light scattering measurements. A mechanism of aggregation of ␤ 2 -m in vivo involving the association of the preformed fibrils with the fraction of I 2 existing at equilibrium is proposed from these results. The possibility of isolating and quantifying a partially folded conformer of ␤ 2 -m involved in the amyloidogenesis process provides new opportunities to monitor hemodialytic procedures aimed at the reduction of such species from the pool of circulating ␤ 2 -m but also to design new pharmaceutical approaches that consider such species as a putative molecular target.Dialysis-related amyloidosis represents an inevitable and severe complication of long term hemodialysis (1-4). Under this pathological condition, protein aggregates known as amyloid fibrils, accumulate in essential tissues, such as the skeletal muscle, interfering with their normal functions. A major constituent of the amyloid fibrils related to this pathological condition is ␤ 2 -microglobulin (␤ 2 -m).1 In its native form, this 99-residue protein is constituted by two ␤-sheets packed against each other to form a fold typical of the immunoglobulin superfamily (5). The two ␤-sheets, constituted by three and four strands, respectively, interact by means of hydrophobic interactions and a disulfide bridge that stabilizes further the ␤-sandwich structure.␤ 2 -m constitutes the light chain of the major histocompatibility complex class I (MHCI). A significant pool of ␤ 2 -m is also normally present in the plasma as a consequence of the constant release from the MHCI to allow the process of catabolic degradation in the kidney (1, 2). In chronic dialysis patients, the artificial membrane induces an inflammatory reaction, which causes the production and release of ␤ 2 -m to increase significantly (6). In addition, ␤ 2 -m cannot be filtered efficiently through the artificial membrane, resulting in an increase of the levels of soluble ␤ 2 -m from 0.3 to 30 g/ml, the range of concentrations observed within healthy individuals, to ϳ40 g/ml (7). The increase of free circulating ␤ 2 -m, the preferential substrate for amyloid deposition by this protein, is responsible, at least in part, for this form of amyloidosis in these patients (1, 2). Big efforts have been expended to improve the biocompatibility and performance of dialysis approaches. ...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

A Partially Structured Species of β2-Microglobulin Is Significantly Populated under Physiological Conditions and Involved in Fibrillogenesis

Chiti

Lorenzi

Grossi

et al. 2001

Journal of Biological Chemistry

144

188

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“…13,14 In 2001, we discovered that β2m is a Cu 2+ -binding protein. 4 Whereas β2m apo is not amyloidogenic, β2m holo is aggregation-prone. …”

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confidence: 99%

Metal binding sheds light on mechanisms of amyloid assembly

Calabrese

Miranker

2009

Prion

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β-2 microglobulin (β2m) is the protein responsible for amyloid deposition in Dialysis-Related Amyloidosis (DRA). Aggregation can be induced by various solution conditions including exposure to divalent metal, incubation at acidic pH, and limited proteolysis. Using Cu 2+ as a trigger, we have trapped, isolated, and crystallized a stable oligomer of β2m that is populated under amyloidogenic solution conditions (Calabrese et al. Nat Struct Mol Biol 2008; 15:965-71). This structure reveals that Cu 2+ -binding is associated with dramatic conformational rearrangements. This has allowed us to postulate a set of structural changes common to all β2m aggregation pathways. Cu 2+ serves as a potential trigger in other aggregation systems such as Aβ, α-synuclein, and mammalian Prion (PrP). A comparison of Cu 2+ binding to β2m and PrP reveals common features. Therefore, in addition to providing insight into DRA, induction of structure by Cu 2+ binding appears to be a recurring structural motif for pathological changes in conformation. Backgroundβ2m is the 99 residue, 12 kDa non-covalent light chain of the Class I Major Histocompatibility Complex (MHC). Its function is to ensure proper folding and cell-surface expression of the MHC. 1 In the course of normal turnover, β2m is released to the serum and catabolized by the kidneys. In patients suffering from endstage renal disease who are treated with hemodialysis therapy, β2m levels rise and amyloid plaques develop throughout the joints and connective tissue. 2 Although an elevated serum level of β2m may be necessary for aggregation, it is not sufficient as β2m remains stably folded at > 1 mM concentration at 37 °C. 3,4 Furthermore, it can be reversibly folded in vitro 5-7 and amyloid is not reported in other diseases with elevated levels in serum. 8,9 Therefore, aggregation must be triggered by features unique to hemodialysis therapy.As β2m exists as a stable monomer under near physiological conditions, 3,10 much effort has been focused on understanding the molecular mechanism by which self association is triggered. Many approaches have been used to induce β2m aggregation. These include limited proteolysis, 11 incubation at acidic pH, 12 and exposure to detergents or organic solvents. 13,14 In 2001, we discovered that β2m is a Cu 2+ -binding protein. 4 Whereas β2m apo is not amyloidogenic, β2m holo is aggregation-prone. Cu 2+ Mediated OligomerizationWe are interested in Cu 2+ -dependent aggregation of β2m for several reasons. First, hemodialysis patients may be exposed to elevated levels of divalent cation as a consequence of therapy. This is apparent in the historical use of Cu 2+ in the preparation of dialysis membranes, and in water quality standards which permit as much as 1.6 μM Cu 2+ in hemodialysate. 15 This is comparable to the ~3 μM affinity of β2m measured in vitro. 4 Second, early experiments revealed that although Cu 2+ is necessary to initiate aggregation, mature fibers remain stable in the presence of a metal chelate. 10 This allowed the possibility that Cu 2+ acti...

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“…This can be accomplished by acidification of the solution (15), truncation of six amino acids from the N terminus (16), or the addition of Cu 2ϩ ions (17). Depending on the denaturing conditions used, a number of different fibril morphologies are formed in vitro (18,19).…”

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confidence: 99%

Co-populated Conformational Ensembles of β2-Microglobulin Uncovered Quantitatively by Electrospray Ionization Mass Spectrometry

Borysik

Radford²,

Ashcroft

2004

Journal of Biological Chemistry

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Ordered assembly of monomeric human ␤ 2 -microglobulin (␤ 2 m) into amyloid fibrils is associated with the disorder hemodialysis-related amyloidosis. Previously, we have shown that under acidic conditions (pH <5.0 at 37°C), wild-type ␤ 2 m assembles spontaneously into fibrils with different morphologies. Under these conditions, ␤ 2 m populates a number of different conformational states in vitro. However, this equilibrium mixture of conformationally different species is difficult to resolve using ensemble techniques such as nuclear magnetic resonance or circular dichroism. Here we use electrospray ionization mass spectrometry to resolve different species of ␤ 2 m populated between pH 6.0 and 2.0. We show that by linear deconvolution of the charge state distributions, the extent to which each conformational ensemble is populated throughout the pH range can be determined and quantified. Thus, at pH 3.6, conditions under which short fibrils are produced, the conformational ensemble is dominated by a charge state distribution centered on the 9؉ ions. By contrast, under more acidic conditions (pH 2.6), where long straight fibrils are formed, the charge state distribution is dominated by the 10؉ and 11؉ ions. The data are reinforced by investigations on two variants of ␤ 2 m (V9A and F30A) that have reduced stability to pH denaturation and show changes in the pH dependence of the charge state distribution that correlate with the decrease in stability measured by tryptophan fluorescence. The data highlight the potential of electrospray ionization mass spectrometry to resolve and quantify complex mixtures of different conformational species, one or more of which may be important in the formation of amyloid.␤ 2 -microglobulin (␤ 2 m) 1 is one of a number of proteins known to aggregate into insoluble amyloid deposits in vivo (1-3). These amyloid deposits have been linked to various human maladies such as Alzheimer's disease (4), Huntington's chorea (5), and senile systemic amyloidosis (6). However, for the majority of the ϳ20 known amyloid-related proteins, the structural mechanism of amyloid formation is still unclear, and, for several proteins, the role that different aggregated states play in the manifestation of the disease symptoms remains unresolved (7).␤ 2 m is a small (11,860-dalton) extracellular protein that forms the nonpolymorphic light chain component of the major histocompatibility class I complex. The physiological role of ␤ 2 m has been likened to a chaperone in that it is required for the heavy chain of the major histocompatibility class I complex to fold into a stable secreted entity (8, 9). ␤ 2 m is an all ␤-sheet protein, with a seven-stranded ␤-sandwich structure and a single disulfide bond linking Cys-25 and Cys-80 in the B and F strands (10) (Fig. 1). In healthy individuals, the serum concentration of circulating free ␤ 2 m is ϳ3 mg⅐liter Ϫ1 (11), and the protein is removed from the serum by renal catabolism (12). In individuals undergoing renal dialysis, the serum concentration of ␤ 2 m can rise to...

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Kidney dialysis-associated amyloidosis: a molecular role for copper in fiber formation

Cited by 161 publications

References 31 publications

A Partially Structured Species of β2-Microglobulin Is Significantly Populated under Physiological Conditions and Involved in Fibrillogenesis

A Partially Structured Species of β2-Microglobulin Is Significantly Populated under Physiological Conditions and Involved in Fibrillogenesis

Metal binding sheds light on mechanisms of amyloid assembly

Co-populated Conformational Ensembles of β2-Microglobulin Uncovered Quantitatively by Electrospray Ionization Mass Spectrometry

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