Researchers from the lab of Dr. Todd O. Yeates, a UCLA professor of chemistry and biochemistry, have published a report in the journal Science desribing the 3D structures of newly discovered bacterial microcompartments. The research might open a new frontier in antibiotic development:
Cells of prokaryotes have been viewed as very primitive, although some contain unusual enclosures known as microcompartments, which appear to serve as primitive organelles inside bacterial cells, carrying out special reactions in their interior.
“Students who take a biology class learn in the first three days that cells of prokaryotes are uniform and without organization, while cells of eukaryotes have a complex organization,” Yeates said. “That contrast is becoming less stark; we are learning there is more of a continuum than a sharp divide. These microcompartments, which resemble viruses because they are built from thousands of protein subunits assembled into a shell-like architecture, are an important component of bacteria. I expect there will be a much greater focus on them now.”
Yeates’ Science paper reveals the first structures of the proteins that make up these shells, and the first high-resolution insights into how they function.
“Those microcompartments have remained shrouded in mystery, largely because of an absence of a detailed understanding of their architecture, of what the structures look like,” said Yeates, who also is a member of the California NanoSystems Institute and UCLA’s Molecular Biology Institute. “The complete three-dimensional structure is still unknown, but in this paper we have provided the first three-dimensional structure of the building blocks of the carboxysome, a protein shell which is the best-studied microcompartment…”
The structure of the carboxysome shows a repeating pattern of six protein molecules packed closely together.
“We didn’t know six would be the magic number,” Yeates said. “What surprises me is how nearly these six protein molecules fill the space between them. If you take six pennies and place them in the shape of a ring, that leaves a large space in the middle. Yet the shape of this protein molecule is such that when six proteins come together, they nearly fill the space; what struck me is how tightly packed they are. That tells us the shell plays an important role in controlling what comes in and goes out. When we saw how the many hexagons come together, we saw that they filled the space tightly as well.”