Protein O-Mannosyltransferases Associate with the Translocon to Modify Translocating Polypeptide Chains

• Verfasst von: Loibl, Martin [VerfasserIn]
• Verfasst von: Hutzler, Johannes [VerfasserIn]
• Verfasst von: Strahl, Sabine [VerfasserIn]
• Titel: Protein O-Mannosyltransferases Associate with the Translocon to Modify Translocating Polypeptide Chains
• Verf.angabe: Martin Loibl, Lina Wunderle, Johannes Hutzler, Benjamin L. Schulz, Markus Aebi, Sabine Strahl
• Umfang: 12 S.
• Fussnoten: Gesehen am 16.05.2017
• Titel Quelle: Enthalten in: The journal of biological chemistry
• Jahr Quelle: 2014
• Band/Heft Quelle: 289(2014), 12, S. 8599-8611
• ISSN Quelle: 1083-351X
• DOI: doi:10.1074/jbc.M113.543116
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 155864699X

Abstract

O-Mannosylation and N-glycosylation are essential protein modifications that are initiated in the endoplasmic reticulum (ER). Protein translocation across the ER membrane and N-glycosylation are highly coordinated processes that take place at the translocon-oligosaccharyltransferase (OST) complex. In analogy, it was assumed that protein O-mannosyltransferases (PMTs) also act at the translocon, however, in recent years it turned out that prolonged ER residence allows O-mannosylation of un-/misfolded proteins or slow folding intermediates by Pmt1-Pmt2 complexes. Here, we reinvestigate protein O-mannosylation in the context of protein translocation. We demonstrate the association of Pmt1-Pmt2 with the OST, the trimeric Sec61, and the tetrameric Sec63 complex in vivo by co-immunoprecipitation. The coordinated interplay between PMTs and OST in vivo is further shown by a comprehensive mass spectrometry-based analysis of N-glycosylation site occupancy in pmtΔ mutants. In addition, we established a microsomal translation/translocation/O-mannosylation system. Using the serine/threonine-rich cell wall protein Ccw5 as a model, we show that PMTs efficiently mannosylate proteins during their translocation into microsomes. This in vitro system will help to unravel mechanistic differences between co- and post-translocational O-mannosylation.