Investigation of serum amyloid a within animal species focusing on the 1-25 amino acid region

AA amyloidosis, characterized by the misfolding of serum amyloid A (SAA) protein, is the most common amyloid protein disorder across multiple species. SAA is a positive-acute phase protein synthesized by the liver in response to inflammation or stress, and it normally associates with high-density lipoprotein at its N-terminus. In this study, we focused on the 1-25 amino acid (aa) region of the complete 104 aa SAA sequence to examine the aggregation propensity of AA amyloid. A library comprising eight peptides from different species was assembled for analysis. To access the aggregation propensity of each peptide region, a bioinformatic study was conducted using the algorithm TANGO. Congo red (CR) binding assays, Thioflavin T (ThT) assays, and transmission electron microscopy (TEM) were utilized to evaluate whether the synthesized peptides formed amyloid-like fibrils. All synthetic SAA 1-25 congeners resulted in amyloid-like fibrils formation (per CR and/or ThT staining and TEM detection) at the exception of the ferret SAA1-25 fragment, which generated plaque-like materials by TEM. Ten residues were preserved among SAA 1-25 congeners resulting in amyloid-like fibrils, i.e. F6, E9, A10, G13, D16, M17, A20, Y21, D23, and M24. Amino acid residues highlighted by this study may have a role in increasing the propensity for amyloid-like fibril formation. This study put an emphasis on region 1-25 in the mechanism of SAA1 misfolding.