Relative quantification of sulfenic acids in plasma proteins using differential labelling and mass spectrometry coupled with 473 nm photo-dissociation analysis: A multiplexed approach applied to an Alzheimer's disease cohort

• Published in: Talanta (Oxford) Vol. 250; p. 123745
• Main Authors: Guillaubez, Jean-Valery, Pitrat, Delphine, Bretonnière, Yann, Lemoine, Jérôme, Girod, Marion
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2022; Elsevier
• Subjects: Alzheimer disease; Analytical chemistry; Biochemistry; Biochemistry, Molecular Biology; biomarkers; Chemical Sciences; cysteine; Cysteine oxidation; derivatization; Differential chromophore derivatization; dissociation; humans; Laser induced dissociation; Life Sciences; Mass spectrometry; oxidation; oxidative stress; peptides; photolysis; protein content; spectrometers; statistical analysis; sulfenic acids; thiols; Cysteine oxidation; Differential chromophore derivatization; Mass spectrometry; Laser induced dissociation; mass spectrometry; laser induced dissociation; cysteine oxidation
• DOI: 10.1016/j.talanta.2022.123745
• ISSN: 0039-9140; 1873-3573

Cysteine (Cys) is subject to a variety of reversible post-translational modifications such as formation of sulfenic acid (Cys-SOH). If this modification is often involved in normal biological activities, it can also be the result of oxidative damage. Indeed, oxidative stress yields abnormal cysteine oxidations that affect protein function and structure and can lead to neurodegenerative diseases. In a context of population ageing, validation of novel biomarkers for detection of neurodegenerative diseases is important. However, Cys-SOH proteins investigation in large human cohorts is challenging due to their low abundance and lability under endogenous conditions. To improve the detection specificity towards the oxidized protein subpopulation, we developed a method that makes use of a mass spectrometer coupled with visible laser induced dissociation (LID) to add a stringent optical specificity to the mass selectivity. Since peptides do not naturally absorb in the visible range, this approach relies on the proper chemical derivatization of Cys-SOH with a chromophore functionalized with a cyclohexanedione. To compensate for the significant variability in total protein expression within the samples and any experimental bias, a normalizing strategy using free thiol (Cys-SH) cysteine peptides derivatized with a maleimide chromophore as internal references was used. Thanks to the differential tagging, oxidative ratios were then obtained for 69 Cys-containing peptides from 19 proteins tracked by parallel reaction monitoring (PRM) LID, in a cohort of 49 human plasma samples from Alzheimer disease (AD) patients. A statistical analysis indicated that, for the proteins monitored, the Cys oxidative ratio does not correlate with the diagnosis of AD. Nevertheless, the PRM-LID method allows the unbiased, sensitive and robust relative quantification of Cys oxidation within cohorts of samples. [Display omitted] •Innovative mass spectrometry coupling with laser induced dissociation @ 473 nm together with differential tagging.•Specific derivatization of cysteine sulfenic acid (Cys-SOH) with a new dabcyl cyclohexadione chromophore.•Normalization using thiol cysteine peptides derivatized with a maleimide chromophore, for calculation of oxidative ratios.•The statistical analysis of the 12 QCs showed CVs of oxidative ratios below 20% for all the targeted peptides.•Multiplexed sensitive, robust, unbiased relative quantification of low concentrated endogenous Cys-SOH plasma proteins.