Electron and X-ray diffraction studies of influenza neuraminidase complexed with monoclonal antibodies

Complexes of influenza virus neuraminidase both with antigen-binding (Fab) fragments and with whole monoclonal antibody molecules have been crystallized. Uniformly thin platelet microcrystals suitable for structure analysis by electron diffraction, yielding reflections to approximately 4.3 A resolution, have been grown from one neuraminidase-Fab complex, that of N9 neuraminidase with 32/3 Fab, and thicker crystals of a second neuraminidase-Fab complex (N9 neuraminidase-NC35 Fab) diffract X-rays to approximately 4.0 A resolution. Electron microscope lattice images of microcrystals both of Fab and of immunoglobulin G complexed with neuraminidase have been interpreted in terms of negatively stained images of the respective individual complex protomers. The sites of binding of the antibodies to the antigen are consistent with the notion that single amino acid changes observed in monoclonal variants of neuraminidase occur in binding epitopes for the antibody used for their selection.