Title : Membrane insertion and topology of the
translocating chain-associating membrane protein (
TRAM )
Abstract :
- The translocating chain-associating membrane protein ( TRAM ) is a glycoprotein involved in the translocation of secreted proteins into the endoplasmic reticulum (ER) lumen and in the insertion of integral membrane proteins into the lipid bilayer
- As a major step toward elucidating the structure of the functional ER translocation/insertion machinery, we have characterized the membrane integration mechanism and the transmembrane topology of TRAM using two approaches: photocross-linking and truncated C-terminal reporter tag fusions.
- Our data indicate that TRAM is recognized by the signal recognition particle and translocon components, and suggest a membrane topology with eight transmembrane segments, including several poorly hydrophobic segments
- Furthermore, we studied the membrane insertion capacity of these poorly hydrophobic segments into the ER membrane by themselves
- Finally, we confirmed the main features of the proposed membrane topology in mammalian cells expressing full-length TRAM