Determining chlorophyll orientation in the CP29 light harvesting complex with arithmetic polarized 2D electronic spectroscopy

CP29, a light harvesting complex (LHC) in photo system II of plants, plays multiple putative roles in vivo: in addition to collecting solar energy, its location at the periphery of the reaction center core implies that excitations originating in other regions of the photosynthetic antenna must be chanelled through it. Furthermore, it has been implicated in the photoprotective nonphotochemical quenching of excess chlorophyll excitations in high light [1]. Nevertheless, the working model for CP29 [2,3] is still relatively uncertain, as it relies on amino acid sequence homology with the major LHC, LHCII, whose x-ray crystal structure has been solved at high resolution. Thus, it is critical to obtain structural information about CP29 directly from experimental data to determine the appropriateness of relying on homology