X-RAY ABSOPTION STUDY ON BACTERIOCHLOROPHYLL ORGANIZATION IN CHLOROSOMES

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Chlorosomes are light harvesting complexes from filamentous and sulphur green photo-synthetic bacteria. The chlorosome is the only photosynthetic antenna complex found in nature in which the chlorophyll molecules are not organized by a protein matrix, but by interactions between the various bacteriochlorophyll (BChl) molecules themselves. It is also the only antenna complex for which structural information is still scarce. One of the active sites guiding the self-assembly of chlorosomes is the central magnesium atom in the BChl porphyrin ring. We aim to elucidate the details of the inter-molecular bonding in chlorosomes by probing the surroundings of the magnesium site with X-ray absorption spectroscopy. The required photon energies range from 1300 eV to 2000 eV and above. Our plan is to compare the BChl bonding in native chlorosomes to a series of polycrystalline chlorophyll samples with known structures. In addition, our simulations show that Mg-coordination numbers and bond lengths to oxygen atoms from neighboring BChl molecules can be obtained from the XANES and EXAFS signals.