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.
In August 2005, Yeates and colleagues reported in the journal Science an underlying principle that governs the assembly of microcompartments: The proteins that form the outer shell form hexagons, which fit together to form extended two-dimensional molecular sheets. The researchers hypothesized that the molecular sheets formed by these hexagons formed the outer shell of the microcompartment and the tiny holes allowed small molecules to move in and out. Yeates and his colleagues have now answered how the shell closes in three dimensions.
Yeates is now studying other microcompartments that are of biomedical importance. Bacteria produce microcompartments when they infect a host, he said.
"We're learning about the kinds of strategies that bacteria have evolved to optimize the efficiency with which they operate or to deal with challenges they face," Yeates said. "In some cases, microcompartments are believed to serve a protective function, protecting the cell."
In the future, Yeates wants to learn how the shell comes to surround the enzymes, how microcompartments are formed and how microcompartments differ from one another. He is also interested in whether it is possible to create "designer microcompartments" that would encase other enzymes.
A key distinction separating the cells of primitive organisms like bacteria, known as prokaryotes, from the cells of complex organisms like humans is that complex, or eukaryotic, cells have
|Contact: Stuart Wolpert|
University of California - Los Angeles