Prion Protein Translocation Mechanism Revealed by Pulling Force Studies

Area of Science:

• Biochemistry
• Molecular Biology
• Neuroscience

Background:

• The mammalian prion protein (PrP) can adopt various topological forms during synthesis.
• Some PrP topologies are linked to neurodegenerative diseases, highlighting the importance of understanding its synthesis.
• The ribosome-Sec61 translocation channel plays a critical role in PrP biogenesis.

Purpose of the Study:

• To investigate the cotranslational folding and translocation mechanisms of the prion protein (PrP).
• To measure the forces acting on the nascent PrP chain during translocation.
• To elucidate how specific sequences influence PrP topology and its link to disease.

Main Methods:

• Utilized an Xbp1-based arrest peptide as a folding sensor coupled to PrP synthesis.
• Measured forces exerted on the nascent PrP chain during translocation through the ribosome-Sec61 complex.
• Analyzed the interaction of specific PrP sequences with the TRAP complex.

Main Results:

• Identified two major and one minor pulling events during PrP nascent chain translocation.
• Demonstrated that a specific intrinsically disordered region interacts with the TRAP complex, modulating the second pulling event.
• Revealed that inefficient translocation, driven by signal sequence and downstream sequences, leads to alternative PrP topologies.

Conclusions:

• The force landscape during PrP synthesis is crucial for determining its final topology.
• Specific sequence elements within PrP, including intrinsically disordered regions, actively modulate translocation dynamics.
• Understanding these mechanisms provides insight into the generation of potentially toxic PrP topologies relevant to neurodegenerative diseases.