FIG 4.

Individual frequency and structural location of amino acid polymorphisms in RSV A F (n = 127) and RSV B F (n = 283) protein sequences. (Top) Major structural features of full-length RSV F protein (amino acids [AA] 1–574), including the extracellular region (F₂: AA 24–109 and F₁: 137-524); SP, signal peptide; p27 peptide; FP, fusion peptide; HR, heptad repeats; and TM/CT, transmembrane/carboxy terminus. (Middle) Linear plot of individual amino acid variation frequency in full-length RSV A F (red) and RSV B F (blue) protein sequences compared to year 2013 RSV A/13-005275 and RSV B/13-001273 reference strains, respectively. Amino acid polymorphisms detected at ≥10% frequency (Table 2) are denoted. (Bottom) Proximal locations of amino acid polymorphisms in antigenic sites of mature prefusion and postfusion RSV F protein trimers. Previously defined antigenic sites (Ø and I to V) (13) are delineated in color. Amino acid positions at which polymorphisms were detected at ≥1% frequency (Table 2) are highlighted in black with adjoining arrows. A and B superscripts denote subtype A and B, respectively.