Aug. 22, 2000 COLUMBUS, Ohio -- Researchers here have determined that a seemingly ordinary protein called YidC found within the membranes of bacteria serves as a gatekeeper of sorts, allowing into the membrane other proteins essential for the bacteria to live. When YidC isn't present, the bacteria die.
The finding surprised scientists who long believed that certain "independent" proteins were able to pass into the membrane on their own. The new discovery, reported in this week's issue of the journal Nature, may suggest a completely new pathway for the translocation of proteins within basic biological units.
Even more startling was the discovery that several other proteins that are remarkably similar to YidC may play similar roles inside mitochondria and in chloroplasts as well. The discovery suggests that bacteria, chloroplasts and mitochondria may all have evolved from a common ancestor.
While YidC has been known to be present in cells for some time, researchers were unclear as to what role it might perform, explained Ross Dalbey, professor of chemistry at Ohio State University. Dalbey and Ph.D student James Samuelson were investigating the protein's role in Escherichia coli bacteria as part of a National Science Foundation-supported study.
"Proteins are synthesized within the cytoplasm of the cell but they then have to be transported, or inserted, either across or into the membranes of organelles within the cell to do their work," Dalbey said. These membranes function as barriers, he said, blocking proteins and other compounds from areas where they don't belong.
In their work, Dalbey and Samuelson developed a strain of the E. coli in which YidC can be depleted. They found that when the YidC was absent, proteins could not migrate into the membranes and the bacteria died.
They also looked at another specific protein called Procoat that was considered "independent," that is, researchers believed it would insert itself into the membrane on its own. But in bacteria lacking YidC, even the Procoat was blocked from entering the membrane. "To everyone's surprise, the protein nearly everybody thought inserted spontaneously requires YidC to succeed in entering the membrane," he said.
The finding of YidC's role in bacteria is even more important when linked to other research on two other basic organelles - chloroplasts in plants and mitochondria in eukaryotic cells. Other teams have found that in mitochondria, a protein called Oxa1 is known to be required for other proteins to migrate into the mitochondrial inner membrane. Without it, there is no migration and the mitochrondia cannot carry out vital cellular processes. A similar protein called Albino3 in the membranes of chloroplasts inside plant cells functions in apparently the same manner. Without it, the chloroplasts can't function.
"The process of membrane insertion is needed for cellular respiration in bacteria and mitochondria, as well as for photosynthesis in chloroplasts," Dalbey said. When scientsts look at the genetic sequences of YidC, Oxa1 and Albino3, Dalbey said, "they are so remarkably similar that it makes you believe they're evolutionarily linked."
The researchers hope that uncovering the function of YidC and related proteins may offer new ways of either enhancing cell function or in accelerating cell death - two mechanisms essential in fighting most diseases, Dalbey said.
Along with Samuelson and Dalbey, Minyong Chen and Fenglei Jiang, both Ph.D students at Ohio State, Ines Moller and Martin Wiedman of Memorial Sloan-Kettering Cancer Center, Andreas Kuhn of the University of Hohenheim and Greg Phillips of Iowa State University all worked on the project.
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