A 63-year-old man has had chronic arthritis for the past 15 years. Physical examination shows ulnar deviation with bony ankylosis producing swan neck deformities of the fingers. Laboratory studies show 4.2 g of protein in a 24-hour urine collection, serum creatinine of 3.1 g/ dL, and urea nitrogen of 3 g/dL. Level of C-reactive protein is markedly elevated. A rectal biopsy is performed, which shows deposition of amorphous pink material with H&E staining in the mucosa. The material stains positive with Congo red. Which of the following proteins is the most likely precursor to this material in the mucosa?