Functional characterization of the trypanosome translational repressor SCD6

Area of Science:

• Molecular Biology
• Cell Biology
• Parasitology

Background:

• Translationally inactive mRNA storage in cytosolic granules allows cellular adaptation.
• Scd6/Rap55 proteins regulate mRNA granules like P-bodies and stress granules in eukaryotes.
• TbSCD6, found in Trypanosoma brucei cytosolic granules, is structurally similar to eukaryotic orthologs.

Purpose of the Study:

• To investigate the function of TbSCD6 in translation and mRNA granule dynamics in Trypanosoma brucei.
• To determine if TbSCD6 interacts with known translational regulators like Dhh1.
• To identify domains responsible for TbSCD6 localization and function.

Main Methods:

• RNA interference (RNAi) for TbSCD6 depletion.
• Analysis of global protein synthesis levels.
• Co-purification assays to identify interacting proteins.
• Mass spectrometry for protein identification and characterization (e.g., methylation).
• Domain analysis of TbSCD6.

Main Results:

• TbSCD6 acts as a general repressor of translation; its depletion leads to increased protein synthesis.
• Steady-state protein levels remain largely unchanged upon TbSCD6 depletion.
• TbSCD6 is not essential for starvation-induced granule formation and does not complex with Dhh1.
• TbSCD6 co-purifies with arginine methyltransferases and is itself methylated.
• Lsm and N-rich domains are crucial for TbSCD6 localization and translational repression.

Conclusions:

• TbSCD6 is a critical regulator of protein synthesis in Trypanosoma brucei, primarily through translational repression.
• Its mechanism differs from yeast and multicellular Scd6 orthologs, particularly regarding Dhh1 interaction.
• Post-translational modification, specifically arginine methylation, and specific domains contribute to TbSCD6's function.