We are interested in all aspects of protein complexes and their properties in the gas phase of a mass spectrometer. Although not the traditional role of this analytical tool, recent developments enable mass spectrometry to probe large intact protein assemblies, providing knowledge of their stoichiometry, topology and interaction partners. I have chosen to highlight two research areas here:
Study of membrane protein complexes
Membrane protein complexes are notoriously difficult to study, particularly those that contain both membrane and soluble protein subunits since in order to maintain solubility, large quantities of detergent are required. Recently we showed however that these complexes, when introduced in detergent micelles, can be liberated from the electrospray droplet. Once in the gas phase, activation of the protein micelle complex yields the largely detergent free complex, enabling accurate mass measurement to reveal subunit stoichiometry, lipid interactions and small molecule binding. (Barrera, N.P., et al. (2008) Micelles protect membrane complexes from solution to vacuum. Science 321, 243-246).
3D models of protein complexes
The ability to generate interaction networks of protein complexes isolated directly from cells enables us to explore all the proteins within an assembly without modifying or removing any constituents. For example the 13-subunit eukaryotic initiation factor 3 (eIF3) was isolated intact (1) and a mass spectrum recorded (2). The complex was then dissociated into a series of building blocks by manipulating the ionic strength of the solution. (3) When these building blocks are pieced together they yield a complete interaction network. Furthermore when collision cross-sections of these components are measured in the gas phase using ion mobility this can lead to the distinction between close-packed and linear arrays of subunits (4). With this information, together with the 27 subcomplexes that were assigned in this study, we were able to build a subunit interaction map constrained by ion mobility restraints and EM density (5). (Zhou, M., et al. (2008) Mass spectrometry reveals modularity and a complete subunit interaction map of the eukaryotic translation factor eIF3. Proc Natl Acad Sci U S A 105, 18139-18144).
Current research group October 2009 taken at Exeter College Oxford at the group awayday.
