Surface proteins, ERAD and antigenic variation in Trypanosoma brucei

Area of Science:

• Molecular biology
• Parasitology
• Cell biology

Background:

• Variant surface glycoprotein (VSG) is crucial for antigenic variation in African trypanosomes.
• Previous studies suggested excess VSG synthesis and degradation via ER-associated degradation (ERAD).

Purpose of the Study:

• To re-evaluate VSG turnover rates in African trypanosomes.
• To confirm the presence and function of ERAD in trypanosomes.
• To investigate the role of ERAD in VSG regulation and parasite survival.

Main Methods:

• Investigated VSG turnover rates using pulse-chase experiments.
• Utilized a mutated ESAG7 subunit (E7:Ty) to assess ERAD function.
• Employed the proteasomal inhibitor MG132 to rescue misfolded protein turnover.
• Assessed the unfolded protein response (UPR) pathway activation.

Main Results:

• No evidence of rapid degradation of newly synthesized VSG was found, supporting regulated synthesis.
• A mutated transferrin receptor subunit (E7:Ty) accumulated in the ER, indicating misfolded protein retention.
• MG132 treatment rescued E7:Ty turnover, confirming proteasomal activity in ERAD.
• ER accumulation of E7:Ty did not induce an unfolded protein response.

Conclusions:

• VSG synthesis is likely precisely regulated, not subject to significant ERAD.
• Functional ERAD exists in trypanosomes and can be confirmed using misfolded protein reporters.
• ERAD may play roles beyond VSG regulation, potentially influencing parasite adaptation and evolution.