Mass-spectrometry-based approaches can bring understanding to the proteins and protein assemblies involved in bacterial photosynthesis.  One complex, Fenna-Matthews-Olson (FMO) protein, a water soluble trimer (150 kDa) and the first photosynthetic complex crystallized and analyzed by x-ray crystallography, mediates energy transfer from the light-harvesting chlorosomes to a membrane-embedded reaction center. For a problem not soluble by x-ray, mass spectrometry-based footprinting  shows the orientation of the complex to permit efficient energy transfer, measures by native spray the number of pigments within the protein, correcting a number that was accepted for many years, and in combination with electron-capture dissociation, maps out flexible regions.  Coupled with HDX, mass spectrometry reveals FMO's interactions with a base plate protein in the chlorosome.  Using crosslinking, MS can also characterize a fully functional megacomplex composed of phycobilisome antenna complex (PBS) and Photosystems I and II from the cyanobacterium Synechocystis PCC 6803. Native spray, in this system, also characterizes  the protective role of Orange Carotenoid Protein showing convincingly how a monomer-dimer equilibrium accommodates excess energy input. MS now provides a clearly power approach that complements optical spectroscopy and other biochemical methods.

Mass spectrometry-based biophysical approaches characterize protein systems in photosynthesis

247th National Meeting (2014)

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