Oxidative protein folding: from thiol-disulfide exchange reactions to the redox poise of the endoplasmic reticulum

Free Radic Biol Med. 2015 Mar;80:171-82. doi: 10.1016/j.freeradbiomed.2014.07.037. Epub 2014 Aug 1.


This review examines oxidative protein folding within the mammalian endoplasmic reticulum (ER) from an enzymological perspective. In protein disulfide isomerase-first (PDI-first) pathways of oxidative protein folding, PDI is the immediate oxidant of reduced client proteins and then addresses disulfide mispairings in a second isomerization phase. In PDI-second pathways the initial oxidation is PDI-independent. Evidence for the rapid reduction of PDI by reduced glutathione is presented in the context of PDI-first pathways. Strategies and challenges are discussed for determination of the concentrations of reduced and oxidized glutathione and of the ratios of PDI(red):PDI(ox). The preponderance of evidence suggests that the mammalian ER is more reducing than first envisaged. The average redox state of major PDI-family members is largely to almost totally reduced. These observations are consistent with model studies showing that oxidative protein folding proceeds most efficiently at a reducing redox poise consistent with a stoichiometric insertion of disulfides into client proteins. After a discussion of the use of natively encoded fluorescent probes to report the glutathione redox poise of the ER, this review concludes with an elaboration of a complementary strategy to discontinuously survey the redox state of as many redox-active disulfides as can be identified by ratiometric LC-MS-MS methods. Consortia of oxidoreductases that are in redox equilibrium can then be identified and compared to the glutathione redox poise of the ER to gain a more detailed understanding of the factors that influence oxidative protein folding within the secretory compartment.

Keywords: Disulfide exchange; Endoplasmic reticulum; Ero1; Glutathione; Oxidative protein folding; Peroxiredoxin; Protein disulfide isomerase; Quiescin sulfhydryl oxidase; Ratiometric mass spectrometry; Redox potential.

Publication types

  • Research Support, N.I.H., Extramural
  • Review

MeSH terms

  • Animals
  • Disulfides / chemistry*
  • Disulfides / metabolism
  • Endoplasmic Reticulum / chemistry
  • Endoplasmic Reticulum / metabolism*
  • Endoplasmic Reticulum / ultrastructure
  • Eukaryotic Cells / cytology
  • Eukaryotic Cells / enzymology
  • Glutathione / chemistry
  • Glutathione / metabolism
  • Glutathione Disulfide / chemistry
  • Glutathione Disulfide / metabolism
  • Humans
  • Kinetics
  • Models, Molecular
  • Oxidation-Reduction
  • Oxidoreductases Acting on Sulfur Group Donors / chemistry*
  • Oxidoreductases Acting on Sulfur Group Donors / metabolism
  • Protein Disulfide-Isomerases / chemistry*
  • Protein Disulfide-Isomerases / metabolism
  • Protein Folding
  • Protozoan Proteins / chemistry*
  • Protozoan Proteins / metabolism
  • Sulfhydryl Compounds / chemistry*
  • Sulfhydryl Compounds / metabolism
  • Trypanosoma brucei brucei / cytology
  • Trypanosoma brucei brucei / enzymology


  • Disulfides
  • Protozoan Proteins
  • Sulfhydryl Compounds
  • Oxidoreductases Acting on Sulfur Group Donors
  • quiescin sulfhydryl oxidase, Trypanosoma brucei
  • Protein Disulfide-Isomerases
  • Glutathione
  • Glutathione Disulfide