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Protein Modifications in the RER

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Modification of secretory and transmembrane proteins entering the rough ER begins in the ER lumen. These modifications aid in protein folding and stabilize the acquired tertiary structure. Protein modifications in the rough ER co-occur at different stages of protein folding.
Broadly, these modifications can be categorized into four main categories — glycosylation, formation of disulfide bonds, assembly of protein subunits, and specific proteolytic cleavages like removal of signal sequences.

Sulfur Assimilation

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Sulfur is an essential element in biological systems, contributing to synthesizing key biomolecules, including amino acids such as cysteine and methionine, and cofactors such as coenzyme A and biotin. Microorganisms primarily assimilate sulfur as sulfate (SO₄²⁻) from the environment, which must undergo a series of biochemical transformations before it can be incorporated into cellular components. As sulfate is highly oxidized, it must undergo assimilatory sulfate reduction to become...

Preparation and Reactions of Sulfides

Preparation and Reactions of Sulfides

Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.

Protein Folding

Protein Folding

Proteins are chains of amino acids linked together by peptide bonds. Upon synthesis, a protein folds into a three-dimensional conformation, critical to its biological function. Interactions between its constituent amino acids guide protein folding, and hence the protein structure is primarily dependent on its amino acid sequence.
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Preparation and Reactions of Thiols

Thiols are prepared using the hydrosulfide anion as a nucleophile in a nucleophilic substitution reaction with alkyl halides. For instance, bromobutane reacts with sodium hydrosulfide to give butanethiol.

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Related Experiment Video

Updated: Jun 10, 2026

Combining Non-reducing SDS-PAGE Analysis and Chemical Crosslinking to Detect Multimeric Complexes Stabilized by Disulfide Linkages in Mammalian Cells in Culture

Combining Non-reducing SDS-PAGE Analysis and Chemical Crosslinking to Detect Multimeric Complexes Stabilized by Disulfide Linkages in Mammalian Cells in Culture

Published on: May 2, 2019

Disulfide bond acquisition through eukaryotic protein evolution.

Jason W H Wong¹, Simon Y W Ho, Philip J Hogg

¹Prince of Wales Clinical School and Lowy Cancer Research Centre, Faculty of Medicine, University of New South Wales, Sydney, New South Wales, Australia.

Molecular Biology and Evolution

|August 3, 2010

Summary

This summary is machine-generated.

Disulfide bonds are highly conserved in proteins, even more so than tryptophan. Their presence correlates with organismal complexity, suggesting positive selection in eukaryotic evolution.

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Combining Non-reducing SDS-PAGE Analysis and Chemical Crosslinking to Detect Multimeric Complexes Stabilized by Disulfide Linkages in Mammalian Cells in Culture

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Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies

Production of Disulfide-stabilized Transmembrane Peptide Complexes for Structural Studies

Published on: March 6, 2013

Area of Science:

Biochemistry
Genomics
Evolutionary Biology

Background:

Disulfide bonds are crucial for protein stability and function.
Previous studies on disulfide bond conservation were limited.
Comparative genomic analysis is needed to understand disulfide bond evolution.

Purpose of the Study:

To analyze the conservation of disulfide bonds across eukaryotic genomes.
To investigate the relationship between disulfide bond acquisition and organismal complexity.
To explore the evolutionary trajectory of disulfide bonds.

Main Methods:

Comparative genomic analysis of disulfide bonds from the Protein Data Bank.
Examination of 29 completely sequenced eukaryotic genomes.
Statistical analysis of cysteine conservation and organismal complexity.

Main Results:

Disulfide-bonded cysteines (half-cystines) are significantly more conserved than unpaired cysteines and other amino acids.
Half-cystines exhibit higher conservation than tryptophan.
Disulfide bond acquisition strongly correlates with organismal complexity.
Disulfide bonds are rarely lost once acquired.
Independent acquisition of disulfide bonds in CD4 protein domain 2 was observed in primates and rodents.

Conclusions:

Disulfide bonds are under strong positive selection in eukaryotic evolution.
The increasing prevalence of disulfide bonds reflects the demand for sophisticated protein functions in complex organisms.
Cysteine usage has increased in modern proteomes.
Evolutionary pathways for disulfide bond formation can be independent.