STT3B-Dependent Posttranslational N-Glycosylation as a Surveillance System for Secretory Protein

• Published in: Molecular cell 2012-07, Vol.47 (1), p.99-110
• Main Authors: Sato, Takashi, Sako, Yasuhiro, Sho, Misato, Momohara, Mamiko, Suico, Mary Ann, Shuto, Tsuyoshi, Nishitoh, Hideki, Okiyoneda, Tsukasa, Kokame, Koichi, Kaneko, Masayuki, Taura, Manabu, Miyata, Masanori, Chosa, Keisuke, Koga, Tomoaki, Morino-Koga, Saori, Wada, Ikuo, Kai, Hirofumi
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; amyloidosis; Azetidinecarboxylic Acid - pharmacology; Calcium-Binding Proteins; cell proliferation; endoplasmic reticulum; Endoplasmic Reticulum - metabolism; Glycosylation - drug effects; HEK293 Cells; Hexosyltransferases - genetics; Hexosyltransferases - metabolism; homeostasis; Humans; hydrophobicity; Immunoblotting; Mannosidases; Membrane Proteins - genetics; Membrane Proteins - metabolism; Models, Biological; Models, Molecular; Molecular Sequence Data; monitoring; mutants; Mutation; Polysaccharides - metabolism; prealbumin; Prealbumin - chemistry; Prealbumin - genetics; Prealbumin - metabolism; Protein Processing, Post-Translational; Protein Structure, Tertiary; Protein Unfolding; RNA Interference; Secretory Pathway - drug effects; Sequence Homology, Amino Acid; sulfhydryl groups; Ubiquitin-Conjugating Enzymes - genetics; Ubiquitin-Conjugating Enzymes - metabolism; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2012.04.015

Nascent secretory proteins are extensively scrutinized at the endoplasmic reticulum (ER). Various signatures of client proteins, including exposure of hydrophobic patches or unpaired sulfhydryls, are coordinately utilized to reduce nonnative proteins in the ER. We report here the cryptic N-glycosylation site as a recognition signal for unfolding of a natively nonglycosylated protein, transthyretin (TTR), involved in familial amyloidosis. Folding and ER-associated degradation (ERAD) perturbation analyses revealed that prolonged TTR unfolding induces externalization of cryptic N-glycosylation site and triggers STT3B-dependent posttranslational N-glycosylation. Inhibition of posttranslational N-glycosylation increases detergent-insoluble TTR aggregates and decreases cell proliferation of mutant TTR-expressing cells. Moreover, this modification provides an alternative pathway for degradation, which is EDEM3-mediated N-glycan-dependent ERAD, distinct from the major pathway of Herp-mediated N-glycan-independent ERAD. Hence we postulate that STT3B-dependent posttranslational N-glycosylation is part of a triage-salvage system recognizing cryptic N-glycosylation sites of secretory proteins to preserve protein homeostasis. [Display omitted] ► A cryptic N-glycosylation site of TTR is posttranslationally glycosylated by STT3B ► N-glycosylation increases the solubility of aggregation-prone TTR ► N-glycosylation of TTR provides an alternative pathway for degradation ► N-glycosylation of TTR depends on the severity of unfolding state