Magic Angle Spinning Nuclear Magnetic Resonance of the Chlorosomes

Abstract

A review. Chlorosomes, the oblong light-harvesting bodies of green photosynthetic bacteria, are attached to the inner side of the cytoplasmic membrane. Magic Angle Spinning NMR (MAS NMR) was used to study isotopically labeled chlorosomes and in vitro model compds. Using uniform isotope labeling of chlorophyll mols., 2D and 3D MAS NMR dipolar correlation spectroscopy was performed in high magnetic field. The chem. shifts provided invaluable information about the structure via ring current effects, while long range correlations were generated that lead to intermol. distance constraints. Novel methodol. was developed and implemented using a Chl a/H2O aggregate, and a structural arrangement of bilayers of Chl sheets with interdigitating tails was resolved. Application of this technol. to chlorosomes and BChl c aggregates provided unambiguous evidence that self-organization of BChl c is the principal structural factor in establishing the rod elements in chlorosomes. This confirms that proteins do not play an essential role in the light harvesting function, which is of fundamental biol. interest. Finally, MAS NMR leads to a bilayer model for the tubular supra-structure of sheets of BChl c in the chlorosomes of Chlorobium tepidum. [on SciFinder(R)]