39 research outputs found
An Asp to Asn mutation is a toxic trigger in beta-2 microglobulin : structure and biophysics
No full textBeta-2 microglobulin (β2m) is part of the Major Histocompatibility Complex Class I (MHC I) and when monomeric becomes an aggregation prone protein that is responsible for a human disorder known as dialysis-related amyloidosis. In 2012 Valleix et al. described a new familial systemic amyloidosis: an unreported β2m mutant (D76N) is the etiological agent of such disease. Main symptoms were chronic diarrhea, loss of weight and polyneuropathy: large amyloid deposits were found in internal organs. From the biophysical point of view, the D76N β2m is much less stable and more amyloidogenic than wt β2m; however, its crystal structure reveals very minor conformational changes compared with the wt protei
A covalent homodimer probing early oligomers along amyloid aggregation
No full textEarly oligomers are crucial in amyloid aggregation; however, due to their transient nature they are among the least structurally characterized species. We focused on the amyloidogenic protein beta2-microglobulin (β2m) whose early oligomers are still a matter of debate. An intermolecular interaction between D strands of facing β2m molecules was repeatedly observed, suggesting that such interface may be relevant for β2m dimerization. In this study, by mutating Ser33 to Cys, and assembling the disulphide-stabilized β2m homodimer (DimC33), such DD strand interface was locked. Although the isolated DimC33 display a stability similar to wt β2m under native conditions, it shows enhanced amyloid aggregation propensity. Three distinct crystal structures of DimC33 suggest that dimerization through the DD interface is instrumental for enhancing DimC33 aggregation propensity. Furthermore, the crystal structure of DimC33 in complex with the amyloid-specific dye Thioflavin-T pinpoints a second interface, which likely participates in the first steps of β2m aggregation. The present data provide new insight into β2m early steps of amyloid aggregation
Wild type beta-2 microglobulin and DE loop mutants display a common fibrillar architecture.
No full textBeta-2 microglobulin (β2m) is the protein responsible for a pathologic condition known as dialysis related amyloidosis. In recent years an important role has been assigned to the peptide loop linking strands D and E (DE loop) in determining β2m stability and amyloid propensity. Several mutants of the DE loop have been studied, showing a good correlation between DE loop geometrical strain, protein stability and aggregation propensity. However, it remains unclear whether the aggregates formed by wild type (wt) β2m and by the DE loop variants are of the same kind, or whether the mutations open new aggregation pathways. In order to address this question, fibrillar samples of wt and mutated β2m variants have been analysed by means of atomic force microscopy and infrared spectroscopy. The data here reported indicate that the DE loop mutants form aggregates with morphology and structural organisation very similar to the wt protein. Therefore, the main effect of β2m DE loop mutations is proposed to stem from the different stabilities of the native fold. Considerations on the structural role of the DE loop in the free monomeric β2m and as part of the Major Histocompatibility Complex are also presented
Class I Major Histocompatibility Complex: the Trojan horse for secretion of amyloidogenic β2-microglobulin.
No full textTo form extracellular aggregates, amyloidogenic proteins bypass the intracellular quality control which normally targets unfolded/aggregated polypeptides. Human D76N β2-microglobulin (β2m) variant is the prototype of unstable and amyloidogenic protein which forms abundant extracellular fibrillar deposits. Here we focus on the role of the Class I Major Histocompatibility Complex (MHC) in the intracellular stabilization of D76N β2m. Using biophysical and structural approaches we show that the MHC containing D76N β2m (MHC76) displays stability, dissociation patterns and crystal structure comparable to those of the MHC with wild type β2m. Conversely, limited proteolysis experiments show a reduced protease susceptibility for D76N β2m within the MHC76 compared to the free variant, suggesting that the MHC has a chaperone-like activity in preventing D76N β2m degradation within the cell. Accordingly, D76N β2m is normally assembled in the MHC and circulates as free plasma species in a transgenic mouse model
Class I Histocompatibility Complex, the Trojan Horse for Secretion of Amyloidogenic β2-Microglobulin
No full textTo form extracellular aggregates, amyloidogenic proteins bypass the intracellular quality control which normally targets unfolded/aggregated polypeptides. Human D76N β2-microglobulin (β2m) variant is the prototype of unstable and amyloidogenic protein which forms abundant extracellular fibrillar deposits. Here we focus on the role of the Class I Major Histocompatibility Complex (MHC) in the intracellular stabilization of D76N β2m. Using biophysical and structural approaches we show that the MHC containing D76N β2m (MHC76) displays stability, dissociation patterns and crystal structure comparable to those of the MHC with wild type β2m. Conversely, limited proteolysis experiments show a reduced protease susceptibility for D76N β2m within the MHC76 compared to the free variant, suggesting that the MHC has a chaperone-like activity in preventing D76N β2m degradation within the cell. Accordingly, D76N β2m is normally assembled in the MHC and circulates as free plasma species in a transgenic mouse model
Structural basis of HMCES interactions with abasic DNA and multivalent substrate recognition
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AFM characterisation of wt β2m and DE loop mutants aggregates incubated for 24 h.
No full text<p>Tapping mode AFM images (top, height data; bottom, amplitude data) of wt β2m and DE loop mutants aggregated for 24h. A-D) Scan size 1.4 μm; the colour bars correspond to a Z range of A) 30 nm; B) 35 nm; C) 100 nm; D) 60 nm. E-H) histograms showing aggregate height measured from cross-sectional profiles in the topographic AFM images. I-L) fibrils found in the pellets of samples A-D). Scan size 860 nm.</p
