title: Influence of the carboxy terminus of serum amyloid A on protein oligomerization, misfolding, and fibril formation.
abstract: The fibrillar deposition of serum amyloid A (SAA) has been linked to the disease amyloid A (AA) amyloidosis. We have used the SAA isoform, SAA2.2, from the CE/J mouse strain, as a model system to explore the inherent structural and biophysical properties of SAA. Despite its nonpathogenic nature in vivo, SAA2.2 spontaneously forms fibrils in vitro, suggesting that SAA proteins are inherently amyloidogenic. However, whereas the importance of the amino terminus of SAA for fibril formation has been well documented, the influence of the proline-rich and presumably disordered carboxy terminus remains poorly understood. To clarify the inherent role of the carboxy terminus in the oligomerization and fibrillation of SAA, we truncated the proline-rich final 13 residues of SAA2.2. We found that unlike full-length SAA2.2, the carboxy-terminal truncated SAA2.2 (SAA2.2ΔC) did not oligomerize to a hexamer or octamer, but formed a high molecular weight soluble aggregate. Moreover, SAA2.2ΔC also exhibited a pronounced decrease in the rate of fibril formation. Intriguingly, when equimolar amounts of denatured SAA2.2 and SAA2.2ΔC were mixed and allowed to refold together, the mixture formed an octamer and exhibited rapid fibrillation kinetics, similar to those for full-length SAA2.2. These results suggest that the carboxy terminus of SAA, which is highly conserved among SAA sequences in all vertebrates, might play important structural roles, including modulating the folding, oligomerization, misfolding, and fibrillation of SAA.
authors.affiliation: Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180, USA.
authors.forename: Sanket
authors.initials: S
authors.lastname: Patke
authors.forename: Ronak
authors.initials: R
authors.lastname: Maheshwari
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Litt
authors.forename: Saipraveen
authors.initials: S
authors.lastname: Srinivasan
authors.forename: J Javier
authors.initials: JJ
authors.lastname: Aguilera
authors.forename: Wilfredo
authors.initials: W
authors.lastname: Colón
authors.forename: Ravi S
authors.initials: RS
authors.lastname: Kane
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D007700:Kinetics; D051379:Mice; D018625:Microscopy, Atomic Force; D008970:Molecular Weight; D017510:Protein Folding; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000685:Serum Amyloid A Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D000682:Amyloid; D020033:Protein Isoforms; C489995:Saa2 protein, mouse; D000685:Serum Amyloid A Protein