The aim of this project is to consolidate preliminary studies on the 3-d structures of influenza virus neuraminidase and of complexes between two antibody molecules (NC41 and NOlO) and the influenza virus antigen neuraminidase. It is a continuation of work supported under NIH grant A121659. Specifically, three tasks will be undertaken. (1) The previously determined structure of NC41 Fab-neuraminidase complex will be defined against the available X-ray diffraction data to 2.8A resolution. The resulting structure will be analyses to enable an accurate description of conformational changes in the neuraminidase which are believed to accompany the binding of this particular antibody (NC41), and to attempt to find a structural correlate of the decrease in enzyme activity when the antibody binds. The refinement will also permit an accurate description of the V-module quaternary structure in the Fab fragment, which has been reported to be unusual. Since the uncommon pairing of VL and VH domains observed in the case of the complexed NC41 antibody might have been induced by antigen, the detailed differences between this and other Fab structures may provide some fundamental insights into immune recognition. (2) The structure of NClO Fab-neuraminidase complex will be determined and refined. The findings from this structure will add to the very small database on antibody-antigen complex structures, and help to clarify the relative importance of adaptable fitting versus rigid bonding in the formation of this important class of macromolecular complexes. (3) The structures of escape mutants of neuraminidase will be completed and crystallization experiments with other monoclonal antibodies and influenza A virus neuraminidases will continue. The knowledge generated from this work will (a) permit a description of two overlapping epitopes of this influenza virus antigen, (b) add to our understanding of antigenic variation in this and other variable viruses (such as HIV), (c) help to provide a general understanding of immune recognition, at least as regards B cell immunity, and (d) aid in the future rational design of synthetic vaccines.
