Orientation of antenna protein in photosynthetic bacteria...( Researchers at Washington University...)

Researchers at Washington University in St. Louis have figured out the orientation of a protein in the antenna complex to its neighboring membrane in a photosynthetic bacterium, a key find in the process of energy transfer in photosynthesis.

Robert Blankenship, Ph.D., Markey Distinguished Professor of biology and chemistry in Arts & Sciences, led a team that for the first time combined chemical labeling with mass spectroscopy to verify the orientation. The team also included Michael Gross, Ph.D., Washington University professor of chemistry, immunology and medicine, and chemistry graduate students Jianzhong Wen and Hao Zhang. A paper describing this work appeared recently in the Proceedings of the National Academy of Sciences USA.

In green sulfur bacteria, which live in extremely dim environments with scarce visible light, the membrane-attached Fenna-Matthews-Olson (FMO) antenna protein serves as a sort of wire connecting the large peripheral chlorosome antenna complex with the organism's reaction center. These bacteria are related to extreme heat-loving bacteria that live at thermal vents on the ocean floor. Their antenna systems are much larger and more pronounced than those of other bacteria to take advantage of whatever geothermal light they can harvest.

Blankenship fondly refers to the FMO protein as the taco shell protein because of its structure: its ribbon-like backbone wraps around three clusters of seven chlorophylls, just like a taco shell around ground beef. The structure also is referred to as trimeric because of the three clusters.

The taco shell is a sort of "middleman" in the antenna system, sandwiched in between a larger antenna and a complex called the reaction center, where all the electron transfer chemistry takes place. Most of the absorption of light is carried out by a complex called the chlorosome that then transfers the energy to the trimeric protein that in turn transfers to the reaction c
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