Non-invasive proteomic analysis of human skin keratins: Screening of methionine oxidation in keratins by mass spectrometry

A missense mutation (rs209302038) of KRT9 gene associated with heat stress in Chinese cattle

Type I keratin 9 encoded by the KRT9 gene serves an important special function either in the mature palmar and plantar skin tissue. The changes in skin conditions and thickening of the outer layer of the skin may be affected by environmental variables. A missense mutation rs209302038 (NC_037346.1: g.41782870 G > A) was detected in KRT9, which changing the isoleucine into valine. This study aimed to identify the frequency of allele in this locus in Chinese indigenous cattle, and analyze the connection with heat stress. Our results indicated that the frequency of allele A gradually decreases from south to north, while the frequency of G allele showed the opposite pattern. Further analysis of the association of the different genotypes with three climate factors, which showed that the genotypes (GG, GA, AA) were significantly related to climatic conditions (p < 0.01). Therefore, we speculated that the mutation of the rs209302038 in Chinese indigenous cattle might be a genetic marker to detect heat stress.

Screening of Chemical Modifications in Human Skin Keratins by Mass Spectrometry-Based Proteomic Analysis via Noninvasive Sampling and On-Tape Digestion

Proteins are continuously exposed to diverse chemical stresses, and the resulting chemical modifications can provide significant information on biological events. Keratins are the main constituent of human skin and are the major target proteins of various chemical modifications. We have previously developed a mass spectrometry-based noninvasive proteomic methodology to screen oxidative modifications in human skin keratins. We have improved this methodology in terms of sample preparation time and amino acid sequence coverage using an on-tape digestion method. After sampling by tape stripping, skin proteins on the tape were subjected to reduction/alkylation, followed by trypsin digestion without a presolubilization step using detergents. To screen chemical modifications in keratins, target modifications and tryptic target peptides carrying the modification sites were determined from in vitro experiments with major reactive chemical species (4-hydroxy-2(E)-nonenal (HNE), 4-oxo-2(E)-nonenal, glucose, methylglyoxal, peroxynitrite, and hydrogen peroxide). The developed method was used to screen target modifications in controls and patients with a swollen red rash. Basal levels of lipid-derived modification, oxidation, nitration, and glycation in keratins were detected in controls. Principal component analysis based on the relative chemical modification resulted in a clear classification of both groups within a 95% confidence interval. Lipid-derived HNE modification increased most significantly in the patient group. This methodology can be easily applied to patients with other diseases, and the target modifications can be used as biomarkers of certain physiological conditions.

An LC/ESI-SRM/MS method to screen chemically modified hemoglobin: simultaneous analysis for oxidized, nitrated, lipidated, and glycated sites

Proteins are continuously exposed to various reactive chemical species (reactive oxygen/nitrogen species, endogenous/exogenous aldehydes/epoxides, etc.) due to physiological and chemical stresses, resulting in various chemical modifications such as oxidation, nitration, glycation/glycoxidation, lipidation/lipoxidation, and adduct formation with drugs/chemicals. Abundant proteins with a long half-life, such as hemoglobin (Hb, t 1/2 63 days, ∼150 mg/mL), are believed to be major targets of reactive chemical species that reflect biological events. Chemical modifications on Hb have been investigated mainly by mechanistic in vitro experiments or in vivo/clinical experiments focused on single target modifications. Here, we describe an optimized LC/ESI-SRM/MS method to screen oxidized, nitrated, lipidated, and glycated sites on Hb. In vivo preliminary results suggest that this method can detect simultaneously the presence of oxidation (+16 Da) of α-Met(32), α-Met(76), β-Met(55), and β-Trp(15) and adducts of malondialdehyde (+54 Da) and glycation (+162 Da) of β-Val(1) in a blood sample from a healthy volunteer. Graphical Abstract Screening chemical modifications on hemoglobin.

Mass spectrometry data from proteomic analysis of human skin keratins after exposure to UV radiation

A mass spectrometry (MS)-based proteomic methodology was employed to monitor oxidative modifications in keratins, the main constituents of human skin (“Non-invasive proteomic analysis of human skin keratins: screening of methionine oxidation in keratins by mass spectrometry” [1], “UV irradiation-induced methionine oxidation in human skin keratins: mass spectrometry-based non-invasive proteomic analysis” [2]). Human skin proteins were obtained non-invasively by tape stripping and solubilized in sodium dodecyl sulfate (SDS) buffer, followed by purification and digestion using the filter-aided sample preparation method. The tryptic peptides were then analyzed by liquid chromatography (LC)/electrospray ionization (ESI)-MS, tandem MS (MS/MS), and LC/ESI-selected reaction monitoring (SRM)/MS. The MS/MS data were generated to confirm amino acid sequences and oxidation sites of tryptic peptides D²⁹⁰VDGAYMTK²⁹⁸ (P1) and N²⁵⁸MQDMVEDYR²⁶⁷ (P2), which contain the most susceptible oxidation sites (Met²⁵⁹, Met²⁶², and Met²⁹⁶ in K1 keratin) upon UVA irradiation [2]. Subsequently, quantitative determination of the relative oxidation levels of P1 and P1 [2] was achieved by LC/ESI-SRM/MS analyses of P1 and P2 together with their oxidized forms after exposure to UVA radiation or treatment with hydrogen peroxide (H₂O₂).

Effects of ionizing radiation on biological molecules--mechanisms of damage and emerging methods of detection

SIGNIFICANCE

The detrimental effects of ionizing radiation (IR) involve a highly orchestrated series of events that are amplified by endogenous signaling and culminating in oxidative damage to DNA, lipids, proteins, and many metabolites. Despite the global impact of IR, the molecular mechanisms underlying tissue damage reveal that many biomolecules are chemoselectively modified by IR.

RECENT ADVANCES

The development of high-throughput "omics" technologies for mapping DNA and protein modifications have revolutionized the study of IR effects on biological systems. Studies in cells, tissues, and biological fluids are used to identify molecular features or biomarkers of IR exposure and response and the molecular mechanisms that regulate their expression or synthesis.

CRITICAL ISSUES

In this review, chemical mechanisms are described for IR-induced modifications of biomolecules along with methods for their detection. Included with the detection methods are crucial experimental considerations and caveats for their use. Additional factors critical to the cellular response to radiation, including alterations in protein expression, metabolomics, and epigenetic factors, are also discussed.

FUTURE DIRECTIONS

Throughout the review, the synergy of combined "omics" technologies such as genomics and epigenomics, proteomics, and metabolomics is highlighted. These are anticipated to lead to new hypotheses to understand IR effects on biological systems and improve IR-based therapies.

[Oxidative stress-mediated chemical modifications to biomacromolecules: mechanism and implication of modifications to human skin keratins and angiotensin II]

Dysregulated production of reactive oxygen species (ROS) during oxidative stress has been associated with a number of inflammatory and age-related degenerative diseases. ROS can directly react with DNA to form oxidized DNA bases. Direct protein oxidation and carbonylation occur on certain amino acid residues resulting in various post-translational modifications. ROS can also initiate the formation of lipid hydroperoxides, which undergo homolytic decomposition to the α,β-unsaturated aldehydic bifunctional electrophiles such as 4-oxo-2(E)-nonenal (ONE) and 4-hydroxy-2(E)-nonenal (HNE). Intracellular generation of highly reactive aldehydes can then result in the formation of DNA and protein adducts. ONE-derived heptanone-etheno and HNE-derived propano DNA adducts have been detected and shown to be mutagenic in a variety of biological systems. In addition, ONE and HNE are involved in protein dysfunctions and altered gene regulations through the modification of amino acid residues and crosslinking of proteins. Our recent study on human skin keratins has identified specific K1 methionine residues as the most susceptible sites to oxidation with hydrogen peroxide, which can be potential biomarkers of oxidative skin damage. The reactions of angiotensin (Ang) II with ONE or HNE produced several modified Ang IIs including a novel pyruvamide-Ang II that formed via oxidative decarboxylation of N-terminal aspartic acid. Subsequently, it has been revealed that the oxidative modifications on the N-terminus of Ang II disrupt interactions with Ang II type 1 receptor and aminopeptidase A, which could affect the regulation of cardiovascular function.

Atopic dermatitis-associated protein interaction network lead to new insights in chronic sulfur mustard skin lesion mechanisms

Chronic sulfur mustard skin lesions (CSMSLs) are the most common complications of sulfur mustard exposure; however, its mechanism is not completely understood.According to clinical signs, there are similarities between CSMSL and atopic dermatitis (AD). In this study, proteomic results of AD were reviewed and the AD-associated protein-protein interaction network (PIN) was analyzed. According to centrality measurements, 16 proteins were designated as pivotal elements in AD mechanisms. Interestingly, most of these proteins had been reported in some sulfur mustard-related studies in late and acute phases separately. Based on the gene enrichment analysis, aging, cell response to stress, cancer, Toll- and NOD-like receptor and apoptosis signaling pathways have the greatest impact on the disease. By the analysis of directed protein interaction networks, it is concluded that TNF, IL-6, AKT1, NOS3 and CDKN1A are the most important proteins. It is possible that these proteins play role in the shared complications of AD and CSMSL including xerosis and itching.

Proteomics methods to study methionine oxidation

The oxidation and consequent reduction of protein-bound methionine residues is of great interest in understanding different aspects of how oxidative stress affects protein functions and cellular signaling. To date, few technologies are available for the study of methionine sulfoxides. And, especially the absence of highly specific antibodies has impeded the field in understanding the exact role of methionine oxidation on a proteome-wide level. Nonetheless, the different models where the responsible enzymes for repair of the oxidized methionines have been studied show that there is an important role for this modification in a cellular context. We here review different mass spectrometry based and proteomics methods for characterizing in vivo methionine oxidation.

Interactions of organophosphates with keratins in the cornified epithelium of human skin

Methods to unequivocally assess and quantify exposure to organophosphate anti-cholinesterase agents are highly valuable, either from a biomonitoring or a forensic perspective. Since for both OP pesticides and various nerve agents the skin is a predominant route of entry, we hypothesized that proteins in the skin might represent an ideal source of unequivocal and persistent biomarkers for exposure to these compounds. In this exploratory study we show that keratin proteins in human skin are relevant binding sites for organophosphates. The thick cornified epithelium of human plantar skin (callus) was exposed to a selection of relevant organophosphorus compounds and keratin proteins were subsequently extracted. After carboxymethylation of cysteine residues, enzymatic digestion of the keratins with pronase and trypsin was performed and the resulting amino acid and peptides were analyzed to assess whether covalent adducts had formed. LC-tandem MS analysis of the pronase digests demonstrated that tyrosine and to a lesser extent serine residues were selectively modified by organophosphate pesticides (both phosphorothioates and the corresponding oxon forms) under physiological conditions. In addition, modification of tyrosine with the nerve agent VX was unequivocally assessed. In order to elucidate specific binding sites, LC-tandem MS analysis of trypsin digests showed two separate tryptic keratin fragments, i.e. LASY*LDK and SLY*GLGGSK, with Y* the modified tyrosine residues, originating from keratin 1/6 and keratin 10, respectively. These preliminary findings, revealing novel binding targets for anti-cholinesterase organophosphates, will form a firm basis for the development of novel (non-invasive) methods for assessment of exposure to organophosphates. Whether this binding will also have biological implications remains an issue for further investigations.