Water-soluble chlorophyll protein (WSCP): Biological function, photophysics, and protein-directed assembly of nanoparticles

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Water-soluble chlorophyll protein (WSCP) is an unusual chlorophyll-binding protein in that (i) it is extremely stable (withstanding boiling water for hours), and (ii), each subunit of about 20 kDa binds no more than 1 chlorophyll a or b molecule and no carotenoid. The biological function of WSCP is unknown, and part of this project will be dedicated to this question, based on the recent finding of highly accumulated WSCP in flower organs of Arabidopsis. The small number of chlorophylls and their close interaction in tetrameric WSCP, the known molecular structure of one WSCP homologue, and the possibility to modify the recombinant protein make WSCP a useful model to study chlorophyll-chlorophyll and chlorophyll-protein interactions. These studies will be done by several spectroscopy groups with whom we will collaborate by providing them with biological material. Finally, we will take advantage of functionalized recombinant WSCP tetramers, to use them as a stable scaffold for organizing oligomers of nanoparticles (NPs). These can be semiconductor NPs (quantum dots) which are able to transfer their excitation energy to the one or two chlorophyll molecules in the center of the WSCP tetramer. Even more exciting is the possibility of sandwiching WSCP between two Au NPs; this arrangement is expected to enhance the WSCP fluorescence drastically due to the local field enhancement and the increased emission rate in the hot spot of the nanoantenna. The various WSCP-NP constructs will be studied on the single-molecule level and in bulk. All sections of the proposal will share the modified versions of recombinant WSCP constructed in this project. Moreover, the project parts will mutually benefit from the information obtained about the biochemical and spectroscopic properties of WSCP.