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Characterization of the oligomerization and aggregation of human Serum Amyloid A.

Patke S, Srinivasan S, Maheshwari R, Srivastava SK, Aguilera JJ, Colón W, Kane RS - PLoS ONE (2013)

Bottom Line: We found that hSAA1.1 formed alpha helix-rich, marginally stable oligomers in vitro on refolding and cross-beta-rich aggregates following incubation at 37°C.Strikingly, while hSAA1.1 was not highly amyloidogenic in vitro, the addition of a single N-terminal methionine residue significantly enhanced the fibrillation propensity of hSAA1.1 and modulated its fibrillation pathway.A deeper understanding of the oligomerization and fibrillation pathway of hSAA1.1 may help elucidate its pathological role.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York, USA.

ABSTRACT
The fibrillation of Serum Amyloid A (SAA) - a major acute phase protein - is believed to play a role in the disease Amyloid A (AA) Amyloidosis. To better understand the amyloid formation pathway of SAA, we characterized the oligomerization, misfolding, and aggregation of a disease-associated isoform of human SAA - human SAA1.1 (hSAA1.1) - using techniques ranging from circular dichroism spectroscopy to atomic force microscopy, fluorescence spectroscopy, immunoblot studies, solubility measurements, and seeding experiments. We found that hSAA1.1 formed alpha helix-rich, marginally stable oligomers in vitro on refolding and cross-beta-rich aggregates following incubation at 37°C. Strikingly, while hSAA1.1 was not highly amyloidogenic in vitro, the addition of a single N-terminal methionine residue significantly enhanced the fibrillation propensity of hSAA1.1 and modulated its fibrillation pathway. A deeper understanding of the oligomerization and fibrillation pathway of hSAA1.1 may help elucidate its pathological role.

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Cartoon representing the proposed pathway for oligomerization and fibrillation of MetSAA1.1 and hSAA1.1.Figures are not drawn to scale.
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pone-0064974-g005: Cartoon representing the proposed pathway for oligomerization and fibrillation of MetSAA1.1 and hSAA1.1.Figures are not drawn to scale.

Mentions: Our AFM studies revealed that hSAA1.1 did not form full-length amyloid fibrils upon incubation at 37°C even after ca. 200 h (Fig. 3D). The low amyloidogenicity of hSAA1.1 in vitro may seem surprising given its pathogenicity in vivo. This result is, however, consistent with our recent studies of murine SAA, where the pathogenic isoform SAA1.1 was found to be less amyloidogenic than the non-pathogenic isoform SAA2.2 [32]. Intriguingly, the addition of a single N-terminal methionine residue greatly enhanced the fibrillation propensity of hSAA1.1 and also modulated its fibrillation pathway. The proposed oligomerization and aggregation pathways for MetSAA1.1 and hSAA1.1 have been summarized in Figure 5. It would be interesting to probe the exact role of the methionine residue in modulating the amyloidogenicity of hSAA1.1 in future work. The ability of MetSAA1.1 to seed the aggregation of “native-like” oligomers of MetSAA1.1 suggests that the N-terminal region containing the methionine might be acting as a “template” for fibril formation. This result is consistent with previous studies that have indicated the importance of the N-terminus for fibril formation [46], and with the ability of N-terminal peptides to form fibrils [22]. However, caution must be exerted while correlating these studies to an in vivo model system especially since recombinantly expressed proteins lack the post-translational modifications typical of mammalian proteins.


Characterization of the oligomerization and aggregation of human Serum Amyloid A.

Patke S, Srinivasan S, Maheshwari R, Srivastava SK, Aguilera JJ, Colón W, Kane RS - PLoS ONE (2013)

Cartoon representing the proposed pathway for oligomerization and fibrillation of MetSAA1.1 and hSAA1.1.Figures are not drawn to scale.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3672174&req=5

pone-0064974-g005: Cartoon representing the proposed pathway for oligomerization and fibrillation of MetSAA1.1 and hSAA1.1.Figures are not drawn to scale.
Mentions: Our AFM studies revealed that hSAA1.1 did not form full-length amyloid fibrils upon incubation at 37°C even after ca. 200 h (Fig. 3D). The low amyloidogenicity of hSAA1.1 in vitro may seem surprising given its pathogenicity in vivo. This result is, however, consistent with our recent studies of murine SAA, where the pathogenic isoform SAA1.1 was found to be less amyloidogenic than the non-pathogenic isoform SAA2.2 [32]. Intriguingly, the addition of a single N-terminal methionine residue greatly enhanced the fibrillation propensity of hSAA1.1 and also modulated its fibrillation pathway. The proposed oligomerization and aggregation pathways for MetSAA1.1 and hSAA1.1 have been summarized in Figure 5. It would be interesting to probe the exact role of the methionine residue in modulating the amyloidogenicity of hSAA1.1 in future work. The ability of MetSAA1.1 to seed the aggregation of “native-like” oligomers of MetSAA1.1 suggests that the N-terminal region containing the methionine might be acting as a “template” for fibril formation. This result is consistent with previous studies that have indicated the importance of the N-terminus for fibril formation [46], and with the ability of N-terminal peptides to form fibrils [22]. However, caution must be exerted while correlating these studies to an in vivo model system especially since recombinantly expressed proteins lack the post-translational modifications typical of mammalian proteins.

Bottom Line: We found that hSAA1.1 formed alpha helix-rich, marginally stable oligomers in vitro on refolding and cross-beta-rich aggregates following incubation at 37°C.Strikingly, while hSAA1.1 was not highly amyloidogenic in vitro, the addition of a single N-terminal methionine residue significantly enhanced the fibrillation propensity of hSAA1.1 and modulated its fibrillation pathway.A deeper understanding of the oligomerization and fibrillation pathway of hSAA1.1 may help elucidate its pathological role.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York, USA.

ABSTRACT
The fibrillation of Serum Amyloid A (SAA) - a major acute phase protein - is believed to play a role in the disease Amyloid A (AA) Amyloidosis. To better understand the amyloid formation pathway of SAA, we characterized the oligomerization, misfolding, and aggregation of a disease-associated isoform of human SAA - human SAA1.1 (hSAA1.1) - using techniques ranging from circular dichroism spectroscopy to atomic force microscopy, fluorescence spectroscopy, immunoblot studies, solubility measurements, and seeding experiments. We found that hSAA1.1 formed alpha helix-rich, marginally stable oligomers in vitro on refolding and cross-beta-rich aggregates following incubation at 37°C. Strikingly, while hSAA1.1 was not highly amyloidogenic in vitro, the addition of a single N-terminal methionine residue significantly enhanced the fibrillation propensity of hSAA1.1 and modulated its fibrillation pathway. A deeper understanding of the oligomerization and fibrillation pathway of hSAA1.1 may help elucidate its pathological role.

Show MeSH
Related in: MedlinePlus