title: Signal peptide peptidase (SPP) assembles with substrates and misfolded membrane proteins into distinct oligomeric complexes.
abstract: 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.
authors.affiliation: Zentrum für Molekulare Biologie der Universität Heidelberg, DKFZ-ZMBH-Allianz, Germany.
authors.forename: Bianca
authors.initials: B
authors.lastname: Schrul
authors.forename: Katja
authors.initials: K
authors.lastname: Kapp
authors.forename: Irmgard
authors.initials: I
authors.lastname: Sinning
authors.forename: Bernhard
authors.initials: B
authors.lastname: Dobberstein
mesh_terms: D016282:Aspartic Acid Endopeptidases / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D002460:Cell Line; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D055355:Opsins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D053719:Tandem Mass Spectrometry
chemical_list: D008565:Membrane Proteins; D055355:Opsins; D016282:Aspartic Acid Endopeptidases; C460085:signal peptide peptidase