In this reporting period we have continued a collaboration with Dr. David Margulies on the characterization of interactions of proteins constituting the peptide loading complex, specifically the TAPBPR protein and its interactions with MHC class I molecules in the presence of different peptides. While we are largely employing analytical ultracentrifugation at the current state, this project involves SPR and fluorescence anisotropy studies and may potentially evolve into a model application for global multi-method analysis of multi-protein interactions. In collaboration with Dr. Mark Mayer, we have continued to study the homo- and hetero-oligomerization of different isoforms of glutamate receptor amino terminal domains. Since the quaternary structure of these receptors controls their ion gating properties, their interactions are of great biological importance. In addition, for us they provide challenging model systems for the development of techniques for studying high-affinity interactions with fluorescence-detected sedimentation velocity. To broaden our experience in this technique, we have also applied it collaboratively to the study tubulin dimer dissociation (with Dr. Dan Sackett), and the self-association properties of several new fluorescent proteins (with Dr. George Patterson). We have also continued our collaboration with Dr. Patrizia Farci applying surface plasmon resonance biosensing to examine the interaction of anti-core antibodies isolated and cloned from livers of patients HBV-associated acute liver failure with their HBV core antigens. The determination of binding epitopes, affinities and kinetics of these antibodies against the homologous core and wild type may provide new insights into the role of these antibodies in the pathogenesis of ALF. We have intensified our long-term collaboration with Dr. Lawrence Samelson on the study of multi-protein interactions in signaling particles after T-cell activation. In more detail, we have explored the hydrodynamic properties of protein constructs that will enable us to study four-component complexes of adapter proteins, and characterize their architecture with regard to the binding stoichiometries and potentially affinities and cooperativity by using multi-signal sedimentation velocity and calorimetric techniques.
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