In mammalian hosts, the African trypanosome parasite replicates freely in the bloodstream, despite being fully exposed to the immune system. To do this, the pathogen relies on the stochastic switching of a Variant Surface Glycoprotein (VSG) for immune evasion.

Now, a study presents the newly discovered ESB2 protein—an active RNA endonuclease—which acts as a “molecular shredder,” allowing the parasite to avoid detection by fine-tuning expression of virulence genes through specialized RNA decay.

Transmitted by the bite of the tsetse fly, if left untreated, the parasites invade the central nervous system, causing neurological issues including severe sleep disruptions, confusion, and coma. This understanding of a previously undescribed mechanism of how the parasite avoids detection with incredible precision may allow researchers to identify new vulnerabilities in its life cycle. It may open the door for future treatments for sleeping sickness—a disease that continues to have a devastating impact on communities across sub-Saharan Africa.

This work is published in Nature Microbiology in the paper, “Specialized RNA decay fine-tunes monogenic antigen expression in Trypanosoma brucei.”

“We’ve discovered that the parasite’s secret to staying invisible isn’t just what it prints, but what it chooses to redact,” noted Joana Faria, PhD, leader of the research group at the University of York. “By placing a ‘molecular shredder’ directly inside its ‘protein factory,’ the parasite can edit its genetic manual in real-time. This suggests a fundamental shift in how we view infection: survival for many organisms may depend less on how they issue genetic instructions and more on how they destroy them at the source.”

The discovery provides an answer to a lingering question in the parasite’s biology that has challenged scientists for 40 years. The genetic manual for the VSG also contains several genes needed for survival and immune evasion. Logic suggests that when the parasite follows these genetic instructions, it should produce equal amounts of each protein. However, the parasite somehow produces a mountain of cloak proteins but only a tiny amount of helper proteins.

By identifying the ESB2 protein, the York team discovered that the parasite controls its genetic messages through destruction rather than just production. ESB2 sits directly inside the parasite’s protein factory, known as the Expression Site Body (ESB). ESB2 acts as a “molecular blade,” ensuring the parasite expresses exactly what it needs to remain hidden from the host’s immune system.

The researchers applied TurboID-mediated proximity labelling mass spectrometry (PL-MS) to “map the ESB post-transcriptional network, identifying three new components: ESB-

associated protein 1 (ESAP1) and ESB-specific proteins 2 and 3 (ESB2 and 3).” They then characterized ESB2 as an RNA endonuclease that negatively regulates ESAG transcripts.

Crucially, they write, they demonstrate that “ESB2 recruitment depends on both its own catalytic activity and a hierarchy involving VEX2, ESAP1, and ESB3.”

“This discovery is a real full-circle moment for me,” added Faria. “The mystery of how this parasite manages the asymmetric expression of its genetic manual has been a cold case in the back of my mind since my days as a postdoc. To finally solve it now, as the first major output of my own lab here at York, is incredibly rewarding. It’s a testament to what a fresh lab and a diverse group of scientists can achieve when they look at an old problem from a completely new angle.”

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