Unusual topogenic sequence directs prion protein biogenesis

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Prion protein (PrP) biosynthesis can yield distinct topological forms.
• These different topologies arise from the same nascent polypeptide chain in cell-free systems.
• System-dependent differences in PrP topology have been observed between wheat germ (WG) extracts and rabbit reticulocyte lysates (RRL).

Purpose of the Study:

• To investigate the topogenic sequence within PrP responsible for system-dependent topology.
• To determine if this sequence's function is translation-dependent.
• To assess the ability to confer system-dependent topology to other proteins.

Main Methods:

• Utilized cell-free translation systems (WG and RRL) with microsomal membranes.
• Analyzed PrP biosynthesis and topology.
• Engineered heterologous proteins by modifying codons to include the identified PrP topogenic sequence.

Main Results:

• A specific topogenic sequence within PrP directs the observed system-dependent topological differences.
• The topogenic sequence's activity was independent of ongoing translation.
• Conferring this sequence to heterologous proteins induced similar system-dependent topology.
• Adding RRL components to WG translation products also influenced topology, suggesting cytosolic factor involvement.

Conclusions:

• The prion protein contains an unusual topogenic sequence that dictates its topology in a cell-free system-dependent manner.
• This sequence's function is independent of translation and can be transferred to other proteins.
• Cytosolic factors likely interact with this sequence to mediate system-dependent topology.