Cysteine Carbamidomethylation (Cysteine CAM) is a modification due to a reaction with iodoacetamide and used to block cysteine from oxidation.
Cysteine residues are reactive substances which can create disulfide bonds between and inside the peptides. Reduction and S-Carboxymethylation (RCM) is used to cap cysteine residues and prevent them from reacting and forming disulfide linkages.
What is it used for?
Peptide Mass fingerprinting is an analytical technique for protein identification and characterization using a mass spectrometer. In order to easily analyses peptide mappings, and because disulfide bridges makes the reverse phase analysis and identification difficult, S-Carboxymethylation of cysteine is performed. Otherwise, proteolytic enzymes need a high pH to digest proteins, and that occurs a disulfide binding. Therefore, Cysteine CAM is an important factor to do peptide mass fingerprinting.
Additionally, RCM is often used prior to protein sequencing and amino acids analysis (AAA).
We have shown previously that at physiologically relevant oxygen tension (pO(2) approximately 10 mmHg), NO S-nitrosylates 1 of approximately 50 free cysteines per ryanodine receptor 1 (RyR1) subunit and transduces a calcium-sensitizing effect on the channel by means of calmodulin (CaM). It has been suggested that cysteine-3635 is part of a CaM-binding domain, and its reactivity is attenuated by CaM [Porter Moore, C., Zhang, J. Z., Hamilton, S. L. (1999) J. Biol. Chem. 274, 36831-36834]. Therefore, we tested the hypothesis that the effect of NO was mediated by C3635. The full-length RyR1 single-site C3635A mutant was generated and expressed in HEK293 cells. The mutation resulted in the loss of CaM-dependent NO modulation of channel activity and reduced S-nitrosylation by NO to background levels but did not affect NO-independent channel modulation by CaM or the redox sensitivity of the channel to O(2) and glutathione. Our results reveal that different cysteines within the channel have been adapted to serve in nitrosative and oxidative responses, and that S-nitrosylation of the cysteine-containing CaM-binding domain underlies the mechanism of CaM-dependent regulation of RyR1 by NO.
A modified hemoglobin tetramer has been prepared containing carbamidomethylated G11(104)alpha cysteine residues. The molecule is electrophoretically identical to hemoglobin A, at pH 8.6, contains 2 titratable sulfhydryl groups per tetramer, and shows a normal oxygen affinity at half-saturation. However, the cooperative oxygen binding is significantly decreased. As the G11(104)alpha cysteine residues are located at the alpha1beta1 contact point in the hemoglobin tetramer, the results of this study indicate that modification within this portion of the molecule does not interfere with the assembly of subunits to form a tetramer or the resultant p50 but can cause a significant alteration of cooperative oxygen binding. In addition, spin-labels attached to this cysteine residue are not sensitive to changes in conformation which may take place at this contact point during oxygen binding. It is therefore possible that modification of the G11(104)alpha cysteine residue abolishes the contribution of the alpha1beta1 contact point to the cooperative oxygen binding phenomenon.
3- Van der Reest, J., Lilla, S., Zheng, L. et al. Nat Commun 9, 1581. 2018
Reactive oxygen species (ROS) are increasingly recognised as important signalling molecules through oxidation of protein cysteine residues. Comprehensive identification of redox-regulated proteins and pathways is crucial to understand ROS-mediated events. Here, we present stable isotope cysteine labelling with iodoacetamide (SICyLIA), a mass spectrometry-based workflow to assess proteome-scale cysteine oxidation. SICyLIA does not require enrichment steps and achieves unbiased proteome-wide sensitivity. Applying SICyLIA to diverse cellular models and primary tissues provides detailed insights into thiol oxidation proteomes. Our results demonstrate that acute and chronic oxidative stress causes oxidation of distinct metabolic proteins, indicating that cysteine oxidation plays a key role in the metabolic adaptation to redox stress. Analysis of mouse kidneys identifies oxidation of proteins circulating in biofluids, through which cellular redox stress can affect whole-body physiology. Obtaining accurate peptide oxidation profiles from complex organs using SICyLIA holds promise for future analysis of patient-derived samples to study human pathologies.
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