Prion protein contains a second endoplasmic reticulum targeting signal sequence located at its C terminus.
Prion protein (PrP) is synthesized at the membrane of the endoplasmic reticulum (ER) in three different topological forms as follows: a fully translocated one ((sec)PrP) and two with opposite orientations in the membrane ((Ntm)PrP and (Ctm)PrP). We asked whether other signal sequences exist in the PrP, other than the N-terminal signal sequence, that contribute to its topological diversity. In vitro translocation assays showed that PrP lacking its N-terminal signal sequence could still translocate into ER microsomes, although at reduced efficiency. Deletion of each of the two hydrophobic regions in PrP revealed that the C-terminally located hydrophobic region (TM2) can function as second signal sequence in PrP. Translocation mediated by the TM2 alone can occur post-translationally and yields mainly (Ctm)PrP, which is implicated in some forms of neurodegeneration in prion diseases. We conclude that, in vitro, PrP can insert into ER membranes co- and post-translationally and can use two different signal sequences. We propose that the unusually complex topology of PrP results from the differential utilization of two signal sequences in PrP.
Zentrum für Molekulare Biologie der Universität Heidelberg, Postfach 106249, 69052 Heidelberg, Germany.
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Hölscher
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UC
Bach
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Dobberstein
D000818:Animals; D010450:Endopeptidases / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism*; D017096:Prion Diseases; D011328:Prions / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014176:Protein Biosynthesis; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017384:Sequence Deletion; D014158:Transcription, Genetic
D011328:Prions; D021382:Protein Sorting Signals; D012333:RNA, Messenger; D011994:Recombinant Proteins; D010450:Endopeptidases