Quality control of ER synthesized proteins: An exposed thiol group as a three-way switch mediating assembly, retention and degradation

Anna M. Fra, Claudio Fagioli, Dario Finazzi, Roberto Sitia, Cristina Alberini

Research output: Contribution to journalArticle

Abstract

Plasma cells secrete IgM only in the polymeric form: the C-terminal cysteine of the μ heavy chain (Cys575) is responsible for both intracellular retention and assembly of IgM subunits. Polymerization is not quantitative, and part of IgM is degraded intracellularly. Neither chloroquine nor brefeldin A (BFA) inhibits degradation, suggesting that this process occurs in a pre-Golgi compartment. Degradation of IgM assembly intermediates requires Cys575: the monomeric IgMala575 mutant is stable also when endoplasmic reticulum (ER) to Golgi transport is blocked by BFA. Addition of the 20 C-terminal residues of μ to the lysosomal protease cathepsin D is sufficient to induce pre-Golgi retention and degradation of the chimeric protein: the small amounts of molecules which exit from the ER are mostly covalent dimers. By contrast, when retained by the KDEL sequence, cathepsin D is stable in the ER, indicating that retention is not sufficient to cause degradation. Replacing the C-terminal cysteine with serine restores transport through the Golgi. As all chimeric cathepsin D constructs display comparable protease activity in vitro, their different fates are not determined by gross alterations in folding. Thus, also out of its normal context, the μ chain Cys575 plays a crucial role in quality control, mediating assembly, retention and degradation.

Original languageEnglish (US)
Pages (from-to)4755-4761
Number of pages7
JournalEMBO Journal
Volume12
Issue number12
StatePublished - 1993

Fingerprint

Sulfhydryl Compounds
Endoplasmic Reticulum
Quality Control
Cathepsin D
Quality control
Immunoglobulin M
Switches
Brefeldin A
Degradation
lysyl-aspartyl-glutamyl-leucine
Cysteine
Proteins
Peptide Hydrolases
Chloroquine
Plasma Cells
Polymerization
Serine
Proteolysis
Dimers
Display devices

Keywords

  • Cathepsin D
  • Degradation
  • Endoplasmic reticulum
  • Immunoglobulin
  • Secretion

ASJC Scopus subject areas

  • Genetics
  • Cell Biology

Cite this

Quality control of ER synthesized proteins : An exposed thiol group as a three-way switch mediating assembly, retention and degradation. / Fra, Anna M.; Fagioli, Claudio; Finazzi, Dario; Sitia, Roberto; Alberini, Cristina.

In: EMBO Journal, Vol. 12, No. 12, 1993, p. 4755-4761.

Research output: Contribution to journalArticle

Fra, Anna M. ; Fagioli, Claudio ; Finazzi, Dario ; Sitia, Roberto ; Alberini, Cristina. / Quality control of ER synthesized proteins : An exposed thiol group as a three-way switch mediating assembly, retention and degradation. In: EMBO Journal. 1993 ; Vol. 12, No. 12. pp. 4755-4761.
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