The Covalent Structure of Amyloid-Related Serum Protein SAA from two Patients with Inflammatory Disease

Abstract
The complete covalent structure of an amyloid-related serum protein SAA from a patient with severe rheumatoid arthritis is presented. The structure was elucidated by N-terminal analyses of the protein as well as on peptides derived from tryptic digestion and after cleaving the protein with BNPS[3-bromo-3-methyl-2-(2-nitrophenylthio-3H-indole)]-skatole. The characterization of tryptic peptide T-9 revealed a polymorphism similar to that seen in protein AA. Structural studies performed on another protein SAA, isolated from a patient with acute systemic lupus erythematosus, indicated that this protein is homologous to that from the rheumatoid arthritis patient. The formation and deposition of the protein AA-containing amyloid fibrils is discussed.