In a recent study, co-led by SciLifeLab National Fellow Jonas Barandun (SciLifeLab/Umeå University), researchers presented near atomic details of the smallest known eukaryotic protein synthesis machine, the microsporidian ribosome. The study was published in Nature Microbiology.

Microsporidia, a group of unicellular spore-forming fungi, known to parasitize almost every animal and with at least 14 different species infecting humans, are a great risk for the environment, agriculture and human health. Even though the US National Institutes of Health (NIH) recently added the parasitic fungi to the list of emerging pathogens of high priority not much is known about their internal molecular machinery.

Together with researchers from The Rockefeller University and Connecticut Agricultural Experiment Station, SciLifeLab researcher Jonas Barandun used cryo-electron microscopy to visualize the microsporidian ribosome, revealing the effect of extreme genome compaction in the process.

Due to the parasitic nature of microsporidian parasites, including the ability to utilize host cell molecules like ATP, they have been able to lose many important genes making their genome the smallest ever described in eukaryotes – even smaller than some bacterial genomes – containing approximately 2000 highly compacted genes.

“Microsporidia are the minimalists among the parasitic eukaryotes, reducing their genome to a minimum which is needed for survival and replication. This makes them ideal model organisms to study minimally required components of a molecular process” says Jonas Barandun, in a press release from Umeå University.

The microsporidia Vairimorpha nectatrix, known to have a ribosomal RNA approximately 30 percent smaller than the rRNA in yeast and 15 percent smaller than the rRNA in E. coli bacteria, was used in the study.

“While it was known that the microsporidian rRNA is significantly smaller than the related yeast rRNA, it was unclear if this compacted rRNA still was able to bind all the eukaryotic ribosomal proteins. Surprisingly, despite the loss of some of their RNA binding sites, almost all ribosomal proteins were still present in the structure, some of them exclusively bound by other ribosomal proteins and not in contact with RNA anymore” explains Jonas in the press release.

Read the full press release here.