Mammalian prions: tolerance to sequence changes-how far?

Area of Science:

• Neuroscience
• Structural Biology
• Molecular Biology

Background:

• Prion diseases involve the misfolding of cellular prion protein (PrP C) into abnormal, aggregated forms (PrP Sc).
• The molecular mechanisms and critical regions of PrP involved in this conversion process remain poorly understood.
• Previous studies indicated minimal sequence changes can disrupt prion replication.

Purpose of the Study:

• To investigate the tolerance of prion replication to substantial sequence modifications in the prion protein.
• To identify regions of PrP critical for conformational conversion and prion infectivity.
• To challenge existing structural models of PrP Sc and the concept of specific prion domains.

Main Methods:

• Employing a reverse genetic approach, introducing amino acid insertions into the H2-H3 inter-helix loop and H2 region of PrP.
• Generating and characterizing bona fide prions with engineered sequence alterations.
• Assessing prion replication and infectivity following sequence modifications.

Main Results:

• Prion replication demonstrated unexpected tolerance to insertions of up to 16 amino acids in the H2-H3 loop and octapeptide insertions in H2.
• Substantial sequence changes in the protease-resistant part of PrP did not abolish prion infectivity.
• The study indicates that prion conversion does not necessitate a specific sequence in the H2-H3 region.

Conclusions:

• Prion protein conversion is remarkably robust to significant sequence alterations, particularly within the protease-resistant region.
• The findings question the necessity of specific sequences or defined N- or C-terminal prion domains within the protease-resistant region for conversion.
• This challenges current structural models of PrP Sc and suggests a more flexible mechanism for prion propagation.