New technology solves mystery of respiration in Tetrahymena

Tetrahymena, a tiny single celled-organism, turns out to be hiding a stunning key: it can be performing respiration—using oxygen to generate mobile energy—differently from other organisms these as plants, animals or yeasts. The discovery, published March 31 in Science, highlights the electric power of new approaches in structural biology and reveals gaps in our awareness of a key department of the tree of daily life.

“We imagined we realized about respiration from researching other organisms, but this displays us how considerably we continue to do not know,” said Maria Maldonado, a postdoctoral researcher in the Office of Molecular and Cellular Biology at the University of California, Davis and co-to start with writer on the paper.

Tetrahymena is a genus of free-living, one-celled organisms generally observed quietly swimming about ponds by beating their coat of little hairs, or cilia. Like us, they are eukaryotes, with their genetic content in a nucleus. They belong to a large and varied group of organisms termed the SAR supergroup. With a several exceptions, these as the malaria parasite Plasmodium, the SAR supergroup is little analyzed.

“It can be a big proportion of the biosphere, but we really don’t believe about them a great deal,” Maldonado stated.

Like all other eukaryotes—and some bacteria—Tetrahymena consume oxygen to generate energy via respiration, explained James Letts, assistant professor of molecular and mobile biology in the UC Davis University of Organic Sciences.

Oxygen will come in at the conclude of the series of chemical reactions included in respiration. Electrons are passed by a chain of proteins situated in buildings identified as cristae in the internal membrane of the mitochondrion. This drives formation of water from oxygen and hydrogen atoms, pumping protons across the membrane, which in change drives development of the ATP, a shop of chemical electricity for the mobile. This electron transportation chain is essential to oxygen-centered respiration in people and other eukaryotes.

New approaches in structural biology

There were being clues that there is a thing unique about the electron transportation chain in Tetrahymena, Letts reported. In the 1970s and 80s, scientists learned that its electron-carrying protein—cytochrome c—and oxygen consuming enzyme at the finish of the chain—terminal oxidase—function in a different way than those people in plants and animals. Right until now, it wasn’t crystal clear accurately how or why these enzymes differed in Tetrahymena when they were conserved throughout other studied eukaryotes.

Maldonado, Letts and co-initial writer Very long Zhou made use of new techniques in structural biology to uncover the Tetrahymena electron transport chain. These integrated a cryo-electron microscopy structural proteomics approach—working out the buildings of massive amount of proteins in a mixed sample at the exact time.

Cryo-electron microscopy freezes samples to particularly low temperatures, building images at just about atomic resolution. Alternatively of imaging a single, purified protein, the staff worked with mixed samples isolated from mitochondrial membranes and then taught an algorithm to identify associated structures.

In this way, they had been in a position to scan via hundreds of hundreds of protein photographs and establish the buildings of 277 proteins in 3 massive assemblies, representing the Tetrahymena electron transport chain at in the vicinity of atomic resolution. Some of these proteins have no matching gene in the recognized Tetrahymena genome database—showing that there will have to be gaps in the readily available reference genome.

By revealing the gaps in our expertise of a reasonably prevalent organism, the work demonstrates our blind places with respect to biodiversity, Letts reported. It also shows the likely of these new approaches in structural biology as a discovery software, he explained.

Portion of the function was conducted with cryo-electron microscopes at the BioEM main facility at the UC Davis College of Biological Sciences. Added authors on the paper are Abhilash Padavannil and Fei Guo, each at UC Davis. Zhou is now at Zhejiang College College of Drugs, Hangzhou, China.