One area of enduring interest for Sibley and his colleagues has been the question of how Toxoplasma and other apicomplexan parasites move themselves around, given their lack of appendages or hairlike structures known as cilia or flagella. Researchers had determined that Toxoplasma has a rotating protein-based conveyor belt on its underside that enables it to move.
To push forward, any rotating object -- be it a belt or a wheel -- needs traction, or the ability to grip onto something and push against that grip. Car wheels, for example, are sometimes given added traction in wintertime via the addition of chains.
The parasite supplies its moving belt with traction by putting spots of an adhesive protein on it. The adhesive protein allows the host to attach to the exterior of the host cell. The resulting contact points give the belt something to push against as it moves backward, in turn pushing the parasite forward.
But these adhesive spots have a significant disadvantage in comparison to a chain: if the belt is to continue rotating, the glue spots have to be cut off at the back or they will jam the belt, greatly reducing the parasite's ability to move and thereby infect a host.
A postdoctoral researcher in Sibley's lab, Fabien Brossier, Ph.D., decided to try to use the recently completed Toxoplasma genome to search for the protein that lets the parasite detach glue spots at the back of the belt. Scientists led by the Institute for Genomic Research in Rockville, Md., posted the completed Toxoplasma genome online last year. Geneticists at Washington University's Genome Sequencing Center contributed to the effort.
Brossier knew the protein that did the work had to be a protease, a protein that cuts or degrades other proteins. He also knew it was likely to belong to a special subcategory known as rhomboid proteases, which are able to clip off sections of proteins near the surfac
Source:Washington University in St. Louis