Generation of prion transmission barriers by mutational control of amyloid conformations

385

437

Over residues 15-36, which comprise the H-bonded core of the amyloid fibrils it forms, the Alzheimer's disease plaque peptide amyloid ␤ (A␤) possesses a very similar sequence to that of another short, amyloidogenic peptide, islet amyloid polypeptide (IAPP). Using elongation rates to quantify seeding efficiency, we inquired into the relationship between primary sequence similarity and seeding efficiency between A␤-(1-40) and amyloid fibrils produced from IAPP as well as other proteins. In both a solution phase and a microtiter plate elongation assay, IAPP fibrils are poor seeds for A␤-(1-40) elongation, exhibiting weight-normalized efficiencies of only 1-2% compared with A␤-(1-40) fibrils. Amyloid fibrils of peptides with sequences completely unrelated to A␤ also exhibit poor to negligible seeding ability for A␤ elongation. Fibrils from a number of point mutants of A␤-(1-40) exhibit intermediate seeding abilities for wild-type A␤ elongation, with differing efficiencies depending on whether or not the mutation is in the amyloid core region. The results suggest that amyloid fibrils from different proteins exhibit structural differences that control seeding efficiencies. Preliminary results also suggest that identical sequences can grow into different conformations of amyloid fibrils as detected by seeding efficiencies. The results have a number of implications for amyloid structure and biology.

Section: Discussionsupporting

confidence: 57%

Seeding Specificity in Amyloid Growth Induced by Heterologous Fibrils

O’Nuallain

Williams

Westermark

et al. 2004

385

437

“…It has been suggested that the morphology of fibrils can be propagated by seeding (23)(24)(25)(26). This was true for the sonication-induced fibrils, since the F3 and F4 fibrils had the same morphology and secondary structure as the F2 fibrils, i.e.…”

Section: Ultrasonication-induced Fibrilmentioning

confidence: 83%

Ultrasonication-induced Amyloid Fibril Formation of β2-Microglobulin

Ohhashi

Kihara

Naiki

et al. 2005

160

167

To obtain insight into the mechanism of fibril formation, we examined the effects of ultrasonication, a strong agitator, on ␤ 2 -microglobulin (␤2-m), a protein responsible for dialysis-related amyloidosis. Upon sonication of an acid-unfolded ␤2-m solution at pH 2.5, thioflavin T fluorescence increased markedly after a lag time of 1-2 h with a simultaneous increase of light scattering. Atomic force microscopy images showed the formation of a large number of short fibrils 3 nm in diameter. When the sonication-induced fibrils were used as seeds in the next seeding experiment at pH 2.5, a rapid and intense formation of long fibrils 3 nm in diameter was observed demonstrating seed-dependent fibril growth. We then examined the effects of sonication on the native ␤2-m at neutral pH, conditions under which amyloid deposits occur in patients. In the presence of 0.5 mM sodium dodecyl sulfate, a model compound of potential trigger and stabilizer of amyloid fibrils in patients, a marked increase of thioflavin T fluorescence was observed after 1 day of sonication at pH 7.0. The products of sonication caused the accelerated fibril formation at pH 7.0. Atomic force microscopy images showed that the fibrils formed at pH 7.0 have a diameter of more than 7 nm, thicker than those prepared at pH 2.5. These results indicate that ultrasonication is one form of agitation triggering the formation of amyloid fibrils of ␤2-m, producing fibrils adapted to the respective pH.Amyloidosis results from the deposition of normally soluble proteins into insoluble amyloid fibrils: long, unbranched, and often twisted fibrillar structures a few nanometers in diameter and predominantly composed of cross ␤-sheets (1-4). Among various amyloidogenic proteins,3 is a target of extensive study because of its clinical importance and suitable size for examining the relation between protein folding and amyloid fibril formation (5-12). Dialysis-related amyloidosis is a common and serious complication in patients receiving hemodialysis for more than 10 years (5, 6). ␤2-m, a typical immunoglobulin domain made of 99 residues, is present as the non-polymorphic light chain of the class I major histocompatibility complex (13). As part of its normal catabolic cycle, ␤2-m dissociates from the class I major histocompatibility complex and is transported in serum to the kidneys where the majority (95%) of it is degraded (6). Renal failure disrupts the clearance of ␤2-m from the serum, and moreover the ␤2-m does not pass through the dialysis membrane, resulting in an increase in the ␤2-m concentration by up to 50-fold in the blood circulation (6). By a mechanism that is currently not well understood, ␤2-m then self-associates to form amyloid fibrils under physiological conditions.The incubation of ␤2-m in vitro under acidic conditions in the presence or absence of seed fibrils results in the formation of high yields of amyloid fibrils with a range of different morphologies (7-11). In contrast, the generation of a substantial amount of amyloid fibrils at neutral pH has be...

“…Although we do not know the precise structure of the amyloid fibrils prepared from the heterologous seeds, critical differences were observed in the fibril diameters between seeded and non-seeded fibrils in the present study. From a view point of structural changes influenced by fibril additives, it is interesting to note the report that changes in the specific structure of fibrils, caused either by mutation (68) or other extrinsic factors (69), are implicated in the onset of prion-like behavior of Sup35. Such changes in the fibril structure might be caused by fibril seeds of the same protein (in the case of Sup35) or different proteins (in the case of the present experiments).…”

Section: Discussionmentioning

confidence: 99%

Amyloid Fibril Formation of α-Synuclein Is Accelerated by Preformed Amyloid Seeds of Other Proteins

Yagi

Kusaka

Hongo

et al. 2005

100

␣-Synuclein is one of the causative proteins of familial Parkinson disease, which is characterized by neuronal inclusions named Lewy bodies. Lewy bodies include not only ␣-synuclein but also aggregates of other proteins. This fact raises a question as to whether the formation of ␣-synuclein amyloid fibrils in Lewy bodies may occur via interaction with fibrils derived from different proteins. To probe this hypothesis, we investigated in vitro fibril formation of human ␣-synuclein in the presence of preformed fibril seeds of various different proteins. We used three proteins, Escherichia coli chaperonin GroES, hen lysozyme, and bovine insulin, all of which have been shown to form amyloid fibrils. Very surprisingly, the formation of ␣-synuclein amyloid fibril was accelerated markedly in the presence of preformed seeds of GroES, lysozyme, and insulin fibrils. The structural characteristics of the natively unfolded state of ␣-synuclein may allow binding to various protein particles, which in turn triggers the formation (extension) of ␣-synuclein amyloid fibrils. This finding is very important for understanding the molecular mechanism of Parkinson disease and also provides interesting implications into the mechanism of transmissible conformational diseases.