PhD defence
Resolving the Dynamic Structure of Chlorosomes in Green Sulfur Bacteria by MAS NMR
- L.A. Dsouza
- Date
- Tuesday 24 February 2026
- Time
- Address
-
Academy Building
Rapenburg 73
2311 GJ Leiden
Supervisor(s)
Summary
Photosynthesis relies on highly efficient light-harvesting systems to initiate energy conversion. In green sulfur bacteria, this function is performed by chlorosomes, the largest known photosynthetic antennae in nature. Chlorosomes are unique because their bacteriochlorophyll molecules self-assemble without a protein scaffold, enabling excitation energy to be transferred with near-unity efficiency over distances of several hundred nanometres. Understanding how this remarkable efficiency arises requires detailed knowledge of both chlorosome structure and molecular dynamics.
This thesis investigates the structure and dynamics of chlorosomes using primarily magic angle spinning (MAS) solid-state nuclear magnetic resonance (NMR), integrated with cryo-electron microscopy, optical spectroscopy, and molecular modelling. By studying chlorosomes from wild-type bacteria as well as genetically modified mutants with reduced structural heterogeneity, well-defined molecular packing motifs could be identified. The results reveal that bacteriochlorophylls form ordered syn-anti parallel stacks with distinct orientations depending on the chlorosome type.
Beyond structure, this work demonstrates that chlorosomes exhibit controlled molecular motion. NMR dipolar coupling measurements provide direct experimental evidence for restricted rotational (librational) motion of the bacteriochlorophyll macrocycles. This motion supports theoretical predictions that dynamic modulation of excitonic energy levels enables ultrafast and highly efficient energy delocalisation throughout the chlorosome. These findings establish chlorosomes as examples of “plastic crystalline” biological materials, combining structural order with functional dynamics.
Finally, the extension of NMR methods to intact bacterial cells shows that chlorosome structure and dynamics can be studied in their native environment. Together, these insights advance our understanding of natural photosynthesis and provide design principles for developing artificial light-harvesting systems for sustainable energy applications.
PhD dissertations
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