UCLA biochemists and colleagues have answered an important question about the structure of microcompartments - the mysterious molecular machines that seem to be present in a wide variety of pathogens and other bacteria.
In the Feb. 22 issue of the journal Science, the biochemists report how the microcompartment structure closes in three dimensions, forming a shell around the enzymes encased inside.
If scientists could prevent or disrupt the formation of these microcompartments, they could probably render the bacteria harmless, said research co-author Todd O. Yeates, UCLA professor of chemistry and biochemistry and a member of the UCLA–Department of Energy Institute of Genomics and Proteomics. They do not yet know how to do this, but the current research may provide a framework for targeting microcompartments.
Yeates and his colleagues have identified the proteins that play the critical role in how the structure folds in the carboxysome, a protein shell that is the best-known and most-studied microcompartment. The shell has a structure like a soccer ball or the large, iconic dome structure at the Walt Disney World's Epcot Center.
"A soccer ball has hexagons and 12 pentagons at the corners; the pentagons are essential to close the structure," said Yeates, who is also a member of the California NanoSystems Institute at UCLA and UCLA's Molecular Biology Institute. "The Epcot Center at Walt Disney World has Spaceship Earth, a well-known dome structure composed of triangles that fit into hexagons, but on closer inspection you will find 12 locations where only five triangles come together; the same is true of the Buckminster Fuller-type domes in the desert and many viral structures.
"This principle of closing a structure by combining a large number of hexagons with a small number of pentagons to create a piece of curvature has been understood by architects, molecular biologists studying viruses and soccer ball manufacturers."
That principle is also understood by microcompartments, in which proteins form 12 pentagons to close the structure; fewer than 12 would not completely close it, said Yeates, who calls the proteins "pentameric carboxysome shell proteins."
The structure of the carboxysome shows a repeating pattern of six protein molecules packed closely together. The carboxysome has more than 3,000 sub-units with six edges and six vertices in a single shell, Yeates said.