Final Report Summary - LARGEMS (The Dynamic Composition of Protein Complexes: A New Perspective in Structural Biology)
Traditionally protein complexes are seen as largely uniform in their composition and functional capacity. However, it is reasonable to speculate that the cell’s population of a specific protein complex actually represents a diverse group of functionally distinct entities. The main aim of the LARGEMS project was to emphasize that such modularity and structural flexibility can exist within a single protein complex. As a model system, we investigated the COP9 signalosome (CSN), an evolutionary conserved multi-subunit complex, which regulates the ubiquitin-proteasome degradation system. Our experimental strategy involved the development and application of native mass spectrometry approaches. Results obtained from this analytical chemistry method were then strengthen by biochemical analyses, fluorescence measurements, and cellular methods. This multidisciplinary approach, integrating in vitro and cellular findings, enabled us to expose the extensive subunit heterogeneity that exists within the CSN complex. Specifically, we determined that almost all of the composing CSN subunits have more than one variant. We also discovered that the specific spatiotemporal composition of the CSN is highly controlled, enabling the complex to rapidly adapt and respond to various cellular conditions. Moreover, we discovered that the CSN embraces an additional subunit, the ninth component of the complex. Altogether, the research conducted in the course of the LARGEMS project actively demonstrated how an integrated mode of analysis, combining chemistry with biology, could provide novel insight that could not have been obtained otherwise.