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.
Hölscher
C
C
Zentrum für Molekulare Biologie der Universität Heidelberg, Postfach 106249, 69052 Heidelberg, Germany.
Bach
U C
UC
Dobberstein
B
B
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