title: Serum amyloid A 2.2 refolds into a octameric oligomer that slowly converts to a more stable hexamer.
abstract: Serum amyloid A (SAA) is an inflammatory protein predominantly bound to high-density lipoprotein in plasma and presumed to play various biological and pathological roles. We previously found that the murine isoform SAA2.2 exists in aqueous solution as a marginally stable hexamer at 4-20°C, but becomes an intrinsically disordered protein at 37°C. Here we show that when urea-denatured SAA2.2 is dialyzed into buffer (pH 8.0, 4°C), it refolds mostly into an octameric species. The octamer transitions to the hexameric structure upon incubation from days to weeks at 4°C, depending on the SAA2.2 concentration. Thermal denaturation of the octamer and hexamer monitored by circular dichroism showed that the octamer is ∼10°C less stable, with a denaturation mid point of ∼22°C. Thus, SAA2.2 becomes kinetically trapped by refolding into a less stable, but more kinetically accessible octameric species. The ability of SAA2.2 to form different oligomeric species in vitro along with its marginal stability, suggest that the structure of SAA might be modulated in vivo to form different biologically relevant species.
authors: Department of Chemistry and Chemical Biology, Rensselaer Polytechnic Institute, Troy, NY 12180, USA.
authors: Yun
authors: Y
authors: Wang
authors: Saipraveen
authors: S
authors: Srinivasan
authors: Zhuqiu
authors: Z
authors: Ye
authors: J
authors: J
authors: Javier Aguilera
authors: Maria M
authors: MM
authors: Lopez
authors: Wilfredo
authors: W
authors: Colón
mesh_terms: D000818:Animals; D007527:Isoenzymes / Q000737:chemistry; D051379:Mice; D011489:Protein Denaturation; D017510:Protein Folding; D055503:Protein Multimerization; D000685:Serum Amyloid A Protein / Q000737:chemistry*; D014508:Urea / Q000737:chemistry
chemical_list: D007527:Isoenzymes; C489995:Saa2 protein, mouse; D000685:Serum Amyloid A Protein; D014508:Urea