A model of the VSG–antibody interaction.

<p>A hypothetical model of immunoglobulin M (IgM) antibody (teal) binding to VSG (pink and blue). The precise arrangement of VSG on the cell membrane (gray) is unknown, but the packing of VSG on the cell membrane is known to be extremely dense. It is unknown whether IgM binds VSG in this particular configuration, but the dense packing of VSG may nevertheless affect the accessibility of antibody to the C-terminus (pink), as illustrated here. The multimeric IgM is also likely to interact with more than one VSG on the cell surface, resulting in the depicted “staple” conformation. The figure was produced by combining (1) the pentameric C-alpha model of IgM (PDB ID 2RCJ), (2) modeling the remainder of the chains using the FG-MD Server [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005784#ppat.1005784.ref008" target="_blank">8</a>] over (3) a planar array of manually positioned VSG N-terminal and C-terminal domains based on the crystal structures of VSG221 (PDB ID 1VSG, 1XU6).