We have significantly extended the capabilities of studying multi-protein complexes by global multi-method analysis (GMMA) by implementing four-component interactions in our SEDPHAT multi-method data analysis software. An example is the formation of a reversible LAT-Gads-Slp76-PLCgamma complex during T-cell signalling, which we have studied by isothermal titration calorimetry (ITC) and sedimentation velocity analytical ultracentrifugation (AUC) for measuring the energetics of complex formation. A second significant improvement of our GMMA capabilities was the implementation of a generic interaction model with arbitrary number of complexes and binding equilibria. This will be extended into the user interface as a model builder and disseminated, so that colleauges can build customized binding models to globally fit biophysical interaction data of more complex systems. We also have enhanced our capability of using total intensity fluorescence data that report on binding-induced changes in fluorescence quantum yield, in joint analysis with sedimentation velocity and other biophysical techniques. This was tested in the study of HIV-1 Gag interactions with nucleic acids in the early stages of viral assembly. This provides an example how the combination of microscopic binding information from fluorescence quench with macroscopic data on homo-and hetero-dimerization measured by sedimentation velocity allows the identification of structural changes associated with different binding steps. Finally, in order to disseminate our SEDPHAT software and facilitate application of multi-method analyses by colleagues, we have organized workshops at NIH and a FEBS Practical Course at Charles University Prague.
