New technology solves mystery of respiration in Tetrahymena

Tetrahymena, a little single celled-organism, turns out to be hiding a astonishing magic formula: it truly is executing respiration—using oxygen to crank out cellular energy—differently from other organisms these types of as plants, animals or yeasts. The discovery, printed March 31 in Science, highlights the ability of new tactics in structural biology and reveals gaps in our knowledge of a important department of the tree of life.

“We thought we knew about respiration from learning other organisms, but this shows us how considerably we still will not know,” claimed Maria Maldonado, a postdoctoral researcher in the Division of Molecular and Cellular Biology at the College of California, Davis and co-first creator on the paper.

Tetrahymena is a genus of totally free-dwelling, one-celled organisms typically discovered quietly swimming all over ponds by beating their coat of very small hairs, or cilia. Like us, they are eukaryotes, with their genetic substance in a nucleus. They belong to a huge and numerous team of organisms known as the SAR supergroup. With a couple exceptions, these kinds of as the malaria parasite Plasmodium, the SAR supergroup is small researched.

“It is really a enormous proportion of the biosphere, but we really don’t think about them considerably,” Maldonado said.

Like all other eukaryotes—and some bacteria—Tetrahymena eat oxygen to crank out vitality by respiration, mentioned James Letts, assistant professor of molecular and cellular biology in the UC Davis School of Organic Sciences.

Oxygen will come in at the conclude of the collection of chemical reactions included in respiration. Electrons are handed via a chain of proteins located in constructions identified as cristae in the inner membrane of the mitochondrion. This drives formation of water from oxygen and hydrogen atoms, pumping protons throughout the membrane, which in switch drives development of the ATP, a keep of chemical energy for the mobile. This electron transportation chain is elementary to oxygen-dependent respiration in individuals and other eukaryotes.

New ways in structural biology

There have been clues that there is a little something diverse about the electron transportation chain in Tetrahymena, Letts stated. In the 1970s and 80s, experts learned that its electron-carrying protein—cytochrome c—and oxygen consuming enzyme at the stop of the chain—terminal oxidase—function otherwise than those in crops and animals. Until finally now, it was not apparent accurately how or why these enzymes differed in Tetrahymena when they ended up conserved across other analyzed eukaryotes.

Maldonado, Letts and co-initial author Long Zhou made use of new approaches in structural biology to uncover the Tetrahymena electron transportation chain. These bundled a cryo-electron microscopy structural proteomics approach—working out the structures of substantial selection of proteins in a blended sample at the same time.

Cryo-electron microscopy freezes samples to exceptionally small temperatures, building photos at practically atomic resolution. Instead of imaging a one, purified protein, the workforce labored with combined samples isolated from mitochondrial membranes and then taught an algorithm to realize associated structures.

In this way, they have been capable to scan through hundreds of hundreds of protein pictures and determine the buildings of 277 proteins in a few significant assemblies, symbolizing the Tetrahymena electron transport chain at in the vicinity of atomic resolution. Some of these proteins have no matching gene in the known Tetrahymena genome database—showing that there must be gaps in the out there reference genome.

By revealing the gaps in our knowledge of a rather frequent organism, the get the job done displays our blind places with regard to biodiversity, Letts stated. It also reveals the potential of these new approaches in structural biology as a discovery software, he claimed.

Part of the operate was conducted with cryo-electron microscopes at the BioEM core facility at the UC Davis College of Organic Sciences. Added authors on the paper are Abhilash Padavannil and Fei Guo, equally at UC Davis. Zhou is now at Zhejiang University University of Drugs, Hangzhou, China.