חדר סמינרים


Dr. Dvir Harris Faculty of Chemistry Massachusetts Institute of Technology, Cambridge, MA, USA

Spectroscopic and structural dynamics in photosynthetic macroassemblies

Mankind strives for efficient and formidable energy resources to meet the ever-growing demand resulted from technological progress. Biological light harvesting operates at near perfect quantum efficiency in the highly dynamic cellular environment, and may provide either the means, or at the very least the designing principles, for such solutions. In my talk I will go over two of my post-doc projects, interrogating the ways different photosynthetic organisms – namely, cyanobacteria and purple bacteria –  overcome environmental stress conditions, at the photosynthetic level. In the first project, we combined single molecule fluorescence spectroscopy and cryogenic electron microscopy (CryoEM), gaining insight on the inherent heterogeneity protein complexes possess. We have found that the 2-MDa cyanobacterial Photosystem I – Iron-Stressed Induced Antenna (PSI-IsiA) super-complex, expressed under iron-limiting conditions, retains strong energetic connectivity albeit structural fluctuations by having multiple energetic pathways from the IsiA antenna system to the PSI reaction center. In the second project, we combined CryoEM and ultrafast transient absorption spectroscopy to investigate the femtosecond energy transfer processes within the photosynthetic network of purple bacteria. We reconstituted two light harvesting antenna complexes (LH3, which is expressed under low light conditions, and LH2) in a membrane-forming lipid bilayer, which is encompassed by amphipathic belting proteins, forming a near-native nanodisc. We have extracted the timescale of energy transfer between LH3 and LH2, and showed that the naturally occurring structural arrangement is a result of optimization between functionality and acclimation flexibility. Altogether, we realized various means by which photosynthetic organisms adapt to environmental stresses, which can be utilized in future biohybrid or bioinspired energetic constructs.