A 35-year-old man with a history of traumatic splenectomy presents to the emergency department with high fever, chills, and a productive cough producing rust-colored sputum. On examination, he is febrile and tachycardic, and auscultation reveals crackles in the right lower lung field. A chest radiograph confirms consolidation in the right lower lobe. Blood cultures grow optochin-sensitive, alpha-hemolytic, gram-positive diplococci. Despite appropriate antibiotic therapy, the patient has persistent bacteremia, and laboratory tests show markedly decreased opsonization of the pathogen. Which bacterial virulence factor is primarily responsible for this organism’s resistance to phagocytosis?