A 2-year-old boy is brought to the emergency department with fever, lethargy, and nuchal rigidity. A lumbar puncture is performed, and cerebrospinal fluid analysis shows elevated neutrophils and protein. Gram stain reveals gram-positive, alpha-hemolytic, optochin-sensitive diplococci. The infectious disease consultant explains that this organism’s major virulence factor impairs opsonization by preventing complement deposition on its surface, thereby evading phagocytosis. Which structural component of this pathogen is primarily responsible for this immune evasion?