A 28-year-old woman from Delhi presents with acute onset fever, headache, and neck stiffness. Lumbar puncture is performed, and cerebrospinal fluid (CSF) shows pleocytosis with predominantly neutrophils, elevated protein, and low glucose. A Gram stain of the CSF reveals Gram-negative diplococci with a kidney bean or coffee bean shape. Blood cultures and CSF cultures are sent. Which of the following structural components of this organism is the primary virulence factor that enables evasion of the complement-mediated bactericidal pathway?