A 52-year-old man complains of pain in his back and fatigue for 6 months. He admits to polyuria and polydipsia. An X-ray film of the upper torso reveals numerous lytic lesions in the lumbar vertebral bodies. Laboratory studies show hypoalbuminemia and mild anemia and thrombocytopenia. A monoclonal immunoglobulin peak is demonstrated by serum electrophoresis, and a bone marrow aspiration demonstrates numerous atypical plasma cells. Urinalysis shows 4+ proteinuria. A renal biopsy in this patient would most likely show deposits of which of the following amyloid precursor proteins?