A 16-year-old college freshman presents to the emergency department with acute onset fever, headache, photophobia, and neck stiffness. He lives in a crowded dormitory and reports being up to date on most childhood immunizations but did not receive the meningococcal conjugate vaccine. Lumbar puncture reveals cloudy cerebrospinal fluid with a neutrophilic predominance. Gram stain shows gram-negative intracellular diplococci. Which virulence factor of this pathogen primarily contributes to its ability to evade phagocytosis through resistance to opsonization?