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Updated: May 8, 2026

Determining Membrane Protein Topology Using Fluorescence Protease Protection (FPP)
Published on: April 20, 2015
TRAP assists membrane protein topogenesis at the mammalian ER membrane
Nicole Sommer1, Tina Junne2, Kai-Uwe Kalies1
1CSCM, Institute of Biology, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany.
Abstract:
Membrane protein insertion and topogenesis generally occur at the Sec61 translocon in the endoplasmic reticulum membrane. During this process, membrane spanning segments may adopt two distinct orientations with either their N- or C-terminus translocated into the ER lumen. While different topogenic determinants in membrane proteins, such as flanking charges, polypeptide folding, and hydrophobicity, have been identified, it is not well understood how the translocon and/or associated components decode them. Here we present evidence that the translocon-associated protein (TRAP) complex is involved in membrane protein topogenesis in vivo. Small interfering RNA (siRNA)-mediated silencing of the TRAP complex in HeLa cells enhanced the topology effect of mutating the flanking charges of a signal-anchor, but not of increasing signal hydrophobicity. The results suggest a role of the TRAP complex in moderating the 'positive-inside' rule.
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