scholarly journals Signal peptide peptidase (SPP) assembles with substrates and misfolded membrane proteins into distinct oligomeric complexes

2010 ◽  
Vol 427 (3) ◽  
pp. 523-534 ◽  
Author(s):  
Bianca Schrul ◽  
Katja Kapp ◽  
Irmgard Sinning ◽  
Bernhard Dobberstein
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Membrane Protein ◽  
Signal Peptide ◽  
Large Range ◽  
Endoplasmic Reticulum Membrane ◽  
Signal Peptides ◽  
Type Ii ◽  
Signal Peptide Peptidase

SPP (signal peptide peptidase) is an aspartyl intramembrane cleaving protease, which processes a subset of signal peptides, and is linked to the quality control of ER (endoplasmic reticulum) membrane proteins. We analysed SPP interactions with signal peptides and other membrane proteins by co-immunoprecipitation assays. We found that SPP interacts specifically and tightly with a large range of newly synthesized membrane proteins, including signal peptides, preproteins and misfolded membrane proteins, but not with all co-expressed type II membrane proteins. Signal peptides are trapped by the catalytically inactive SPP mutant SPPD/A. Preproteins and misfolded membrane proteins interact with both SPP and the SPPD/A mutant, and are not substrates for SPP-mediated intramembrane proteolysis. Proteins interacting with SPP are found in distinct complexes of different sizes. A signal peptide is mainly trapped in a 200 kDa SPP complex, whereas a preprotein is predominantly found in a 600 kDa SPP complex. A misfolded membrane protein is detected in 200, 400 and 600 kDa SPP complexes. We conclude that SPP not only processes signal peptides, but also collects preproteins and misfolded membrane proteins that are destined for disposal.

Intramembrane proteolysis and post-targeting functions of signal peptides

2003 ◽  
Vol 31 (6) ◽  
pp. 1243-1247 ◽  
Author(s):  
B. Martoglio
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Bilayer ◽  
Signal Peptide ◽  
Eukaryotic Cells ◽  
Endoplasmic Reticulum Membrane ◽  
Signal Peptides ◽  
Peptide Fragments ◽  
Intramembrane Proteolysis ◽  
Signal Sequences ◽  
Membrane Spanning

Signal sequences are the addresses of proteins destined for secretion. In eukaryotic cells, they mediate targeting to the endoplasmic reticulum membrane and insertion into the translocon. Thereafter, signal sequences are cleaved from the pre-protein and liberated into the endoplasmic reticulum membrane. We have recently reported that some liberated signal peptides are further processed by the intramembrane-cleaving aspartic protease signal peptide peptidase. Cleavage in the membrane-spanning portion of the signal peptide promotes the release of signal peptide fragments from the lipid bilayer. Typical processes that include intramembrane proteolysis is the regulatory or signalling function of cleavage products. Likewise, signal peptide fragments liberated upon intramembrane cleavage may promote such post-targeting functions in the cell.

Molecular insights into mechanisms of intramembrane proteolysis through signal peptide peptidase (SPP)

2010 ◽  
Vol 427 (3) ◽  
pp. e1-e3 ◽  
Author(s):  
Bernd Schröder ◽  
Paul Saftig
Keyword(s):  
Membrane Protein ◽  
Signal Peptide ◽  
Cell Signalling ◽  
Dominant Negative ◽  
Signal Peptides ◽  
Intramembrane Proteolysis ◽  
Independent Manner ◽  
Interacting Protein ◽  
Signal Peptide Peptidase ◽  
Signalling Molecules

The processing of membrane-anchored signalling molecules and transcription factors by RIP (regulated intramembrane proteolysis) is a major signalling paradigm in eukaryotic cells. Intramembrane cleaving proteases liberate fragments from membrane-bound precursor proteins which typically fulfil functions such as cell signalling and regulation, immunosurveillance and intercellular communication. Furthermore, they are thought to be involved in the development and propagation of several diseases, such as Alzheimer's disease and hepatitis C virus infection. In this issue of the Biochemical Journal, Schrul and colleagues investigate the interaction of the endoplasmic reticulum-resident intramembrane cleaving SPP (signal peptide peptidase) with different type II oriented transmembrane proteins. A combination of co-immunoprecipitation experiments using wild-type and a dominant-negative SPP with electrophoretic protein separations under native conditions revealed selectivity of the interaction. Depending on the interacting protein, SPP formed complexes of different sizes. SPP could build tight interactions not only with signal peptides, but also with pre- and mis-folded proteins. Whereas signal peptides are direct substrates for SPP proteolysis, the study suggests that SPP may be involved in the controlled sequestration of possibly toxic membrane protein species in a proteolysis-independent manner. These large oligomeric membrane protein aggregates may then be degraded by the proteasome or autophagy.

scholarly journals An ATP-binding membrane protein is required for protein translocation across the endoplasmic reticulum membrane.

1991 ◽  
Vol 2 (10) ◽  
pp. 851-859 ◽  
Author(s):  
D L Zimmerman ◽  
P Walter
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Membrane Protein ◽  
Protein Translocation ◽  
Signal Sequence ◽  
Microsomal Membrane ◽  
Atp Binding ◽  
Endoplasmic Reticulum Membrane ◽  
Receptor Complex

The role of nucleotides in providing energy for polypeptide transfer across the endoplasmic reticulum (ER) membrane is still unknown. To address this question, we treated ER-derived mammalian microsomal vesicles with a photoactivatable analogue of ATP, 8-N3ATP. This treatment resulted in a progressive inhibition of translocation activity. Approximately 20 microsomal membrane proteins were labeled by [alpha 32P]8-N3ATP. Two of these were identified as proteins with putative roles in translocation, alpha signal sequence receptor (SSR), the 35-kDa subunit of the signal sequence receptor complex, and ER-p180, a putative ribosome receptor. We found that there was a positive correlation between inactivation of translocation activity and photolabeling of alpha SSR. In contrast, our data demonstrate that the ATP-binding domain of ER-p180 is dispensable for translocation activity and does not contribute to the observed 8-N3ATP sensitivity of the microsomal vesicles.

scholarly journals The C-terminal tail guides assembly and degradation of membrane proteins

2019 ◽  
Author(s):  
Sha Sun ◽  
Malaiyalam Mariappan
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Membrane Protein ◽  
Nuclear Membrane ◽  
Time Window ◽  
Protein Complexes ◽  
Long Tails ◽  
Membrane Protein Complexes ◽  
Biochemical Features

SUMMARYA large number of newly synthesized membrane proteins in the endoplasmic reticulum (ER) are assembled into multi-protein complexes, but little is known about the mechanisms required for either assembly or degradation of unassembled membrane proteins. We find that C-terminal transmembrane domains (C-TMDs) with shorter tails are inefficiently inserted into the ER membrane since the translation is terminated before they emerge from ribosomes. These TMDs of insufficient hydrophobicity are post-translationally retained by the Sec61 translocon, thus providing a time window for efficient assembly with TMDs from partner membrane proteins. The unassembled C-TMDs are slowly flipped into the ER lumen. While the luminal chaperone BiP captures flipped C-TMDs with long tails and routes them to the ER-associated quality control, C-TMDs with shorter tails are diffused into the nuclear membrane. Thus, our studies suggest that C-terminal tails harbor important biochemical features for both biosynthesis and quality control of membrane protein complexes.

TMCC3 localizes at the three-way junctions for the proper tubular network of the endoplasmic reticulum

2019 ◽  
Vol 476 (21) ◽  
pp. 3241-3260
Author(s):  
Sindhu Wisesa ◽  
Yasunori Yamamoto ◽  
Toshiaki Sakisaka
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Membrane Protein ◽  
Mammalian Cells ◽  
Coiled Coil ◽  
Transmembrane Domains ◽  
Domain Family ◽  
Coiled Coil Domain ◽  
U2os Cells ◽  
Er Membrane

The tubular network of the endoplasmic reticulum (ER) is formed by connecting ER tubules through three-way junctions. Two classes of the conserved ER membrane proteins, atlastins and lunapark, have been shown to reside at the three-way junctions so far and be involved in the generation and stabilization of the three-way junctions. In this study, we report TMCC3 (transmembrane and coiled-coil domain family 3), a member of the TEX28 family, as another ER membrane protein that resides at the three-way junctions in mammalian cells. When the TEX28 family members were transfected into U2OS cells, TMCC3 specifically localized at the three-way junctions in the peripheral ER. TMCC3 bound to atlastins through the C-terminal transmembrane domains. A TMCC3 mutant lacking the N-terminal coiled-coil domain abolished localization to the three-way junctions, suggesting that TMCC3 localized independently of binding to atlastins. TMCC3 knockdown caused a decrease in the number of three-way junctions and expansion of ER sheets, leading to a reduction of the tubular ER network in U2OS cells. The TMCC3 knockdown phenotype was partially rescued by the overexpression of atlastin-2, suggesting that TMCC3 knockdown would decrease the activity of atlastins. These results indicate that TMCC3 localizes at the three-way junctions for the proper tubular ER network.

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