The team then went a step further and used solid-state NMR spectroscopy -- a technique in which samples are spun very rapidly and exposed to a magnetic field -- to look deep inside the chlorosome. This technique enables researchers to understand the relationships between atomic nuclei in a sample and, ultimately, to acquire structural information about the molecules of interest.
"The NMR data revealed to us that the individual chlorophyll molecules in green bacteria are arranged in dimers -- molecules consisting of two identical simpler molecules -- with their long hydrophobic, or water-repellent, tails sticking out of either side," said Bryant. "We also learned precisely how the chlorophyll molecules attach to one another, and we were able to measure the distance between chlorophyll molecules. The cryo-electron microscopy pictures showed gross structural details and distances, and the NMR results allowed us to quantify these distances as well, and confirmed to us that what were were seeing was, in fact, stacks of the chlorophyll molecules all lined up," he said. The NMR results also enabled the scientists to determine that the chlorophyll molecules in green bacteria are arranged in helical spirals. In the mutant bacteria, the chlorophyll molecules are positioned at a nearly 90-degree angle in relation to the long axis of the nanotubes, whereas the angle is less steep in the wild-type organism. "It's the orientation of the chlorophyll molecules that is the most important thing here," said Bryant. The last steps for the team were to pull together all of their data and
|Contact: Barbara K. Kennedy|