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. 2009 May 13;106(21):8701–8706. doi: 10.1073/pnas.0903427106

Fig. 1.

Fig. 1.

HA and antibody interference. (A) Globular head of a monomer of HA (Protein Data Bank ID code 1hgf), showing five antibody-binding sites (or epitopes) and the receptor-binding site. The figure was drawn by using the PyMOL molecular graphics system. (B) Interference between antibodies that bind to two different HA epitopes. Illustrated are cross-sections of an IgG molecule and an HA trimer. The molecules were drawn approximately to scale. IgG is a Y-shaped molecule that can be separated into three fragments (two Fab fragments and one Fc fragment) of approximately the same size. A Fab fragment has approximate dimensions 80 × 50 × 40 Å (7). In comparison, an HA trimer has a length of ≈135 Å and a diameter of ≈55 Å (8), approximately equal to the width of the 40- × 50-Å distal surface of a Fab fragment, which contains the Fab-binding pocket.