Protein glycosylation plays key roles in many biological processes. In addition, alterations in protein glycosylation have been related to different diseases, as well as may affect the properties of recombinant proteins used as human therapeutics. For this reason, protein glycosylation analysis is of main interest in biomedical and biopharmaceutical research. Although recent advances in LC-MS analysis have made possible glycoprotein glycosylation site identification, characterization of glycoprotein glycan structures, as well as glycoprotein identification and quantification, protein glycosylation analysis in complex samples still remains a difficult task. This is due to low proportions of glycopeptides in comparison to peptides obtained after glycoprotein digestion, the suppression of the glycopeptide MS signals in the presence of peptides, and the high heterogeneity of glycopeptides. Thus, in the recent years, continuous efforts have been devoted to the development of glycopeptide enrichment and separation strategies to facilitate and improve glycoprotein glycosylation analysis in complex samples. This review summarizes the different methodologies that can be employed for glycopeptide enrichment/separation from complex samples including methods based on lectin affinity enrichment, covalent interactions, or chromatographic separations and solid-phase extraction.

Lysine acetylations are reversible posttranslational modifications of histone and non-histone proteins that play important regulatory roles in signal transduction cascades and gene expression. Lysine acetylations are regulated by histone acetyltransferases as writers and histone deacetylases as erasers. Because of their role in signal transduction cascades, these enzymes are important players in inflammation. Therefore, applications of histone acetyltransferase inhibitors to reduce inflammatory responses are interesting. Among the few histone acetyltransferase inhibitors described, C646 is one of the most potent (Ki of 0.4 μM for histone acetyltransferase p300). C646 was described to regulate the NF-κB pathway; an important pathway in inflammatory responses, which is regulated by acetylation. Interestingly, this pathway has been implicated in asthma and COPD. Therefore we hypothesized that via regulation of the NF-κB signaling pathway, C646 can inhibit pro-inflammatory gene expression, and have potential for the treatment of inflammatory lung diseases. In line with this, here we demonstrate that C646 reduces pro-inflammatory gene expression in RAW264.7 murine macrophages and murine precision-cut lung slices. To unravel its effects on cellular substrates we applied mass spectrometry and found, counterintuitively, a slight increase in acetylation of histone H3. Based on this finding, and structural features of C646, we presumed inhibitory activity of C646 on histone deacetylases, and indeed found inhibition of histone deacetylases from 7 μM and higher concentrations. This indicates that C646 has potential for further development towards applications in the treatment of inflammation, however, its newly discovered lack of selectivity at higher concentrations needs to be taken into account.

We developed a discovery-validation mass-spectrometry-based pipeline to identify a set of proteins that are regulated in serum of patients with cervical intraepithelial neoplasia (CIN) and squamous cell cervical cancer using iTRAQ, label-free shotgun, and targeted mass-spectrometric quantification. In the discovery stage we used a "pooling" strategy for the comparative analysis of immunodepleted serum and revealed 15 up- and 26 down-regulated proteins in patients with early- (CES) and late-stage (CLS) cervical cancer. The analysis of nondepleted serum samples from patients with CIN, CES, an CLS and healthy controls showed significant changes in abundance of alpha-1-acid glycoprotein 1, alpha-1-antitrypsin, serotransferrin, haptoglobin, alpha-2-HS-glycoprotein, and vitamin D-binding protein. We validated our findings using a fast UHPLC/MRM method in an independent set of serum samples from patients with cervical cancer or CIN and healthy controls as well as serum samples from patients with ovarian cancer (more than 400 samples in total). The panel of six proteins showed 67% sensitivity and 88% specificity for discrimination of patients with CIN from healthy controls, a stage of the disease where current protein-based biomarkers, for example, squamous cell carcinoma antigen (SCCA), fail to show any discrimination. Additionally, combining the six-protein panel with SCCA improves the discrimination of patients with CES and CLS from healthy controls.

Proteome profiling of crude serum is a challenging task due to the wide dynamic range of protein concentrations and the presence of high-abundance proteins, which cover >90% of the total protein mass in serum. Peptide fractionation on strong cation exchange, weak anion exchange in the electrostatic repulsion hydrophilic interaction chromatography (ERLIC) mode, RP C18 at pH 2.5 (low pH), fused-core fluorinated at pH 2.5, and RP C18 at pH 9.7 (high pH) stationary phases resulted in two to three times more identified proteins and three to four times more identified peptides in comparison with 1D nanoChip-LC-MS/MS quadrupole TOF analysis (45 proteins, 185 peptides). The largest number of peptides and proteins was identified after prefractionation in the ERLIC mode due to the more uniform distribution of peptides among the collected fractions and on the RP column at high pH due to the high efficiency of RP separations and the complementary selectivity of both techniques to low-pH RP chromatography. A 3D separation scheme combining ERLIC, high-pH RP, and low-pH nanoChip-LC-MS/MS for crude serum proteome profiling resulted in the identification of 208 proteins and 1088 peptides with the lowest reported concentration of 11 ng/mL for heat shock protein 74.

Purpose: The objective of this study is to better understand factors governing the variability and sensitivity in SRM and PRM, compared to immunoassay. Experimental design: A 2D-LC-MS/MS-based SRM and PRM assay is developed for quantitative measurements of HSP90α in serum. Forty-three control sera are compared by SRM, PRM, and ELISA following the manufacturer's instructions. Serum samples are trypsin-digested and fractionated by strong cation exchange chromatography prior to SRM and PRM measurements. Analytical parameters such as linearity, LOD, LOQ, repeatability, and reproducibility of the SRM, PRM, and ELISA are determined. Results: PRM data obtained by high-resolution MS correlate better with ELISA measurements than SRM data measured on a triple quadrupole mass spectrometer. While all three methods (SRM, PRM, and ELISA) are able to quantify HSP90α in serum at the ng mL -1 level, the use of PRM on a high-resolution mass spectrometer reduces variation and shows comparable sensitivity to immunoassay. Conclusions and clinical relevance: Using fractionation, it is possible to measure ng mL -1 levels of HSP90α in a reproducible, selective, and sensitive way using PRM in serum. This opens up the possibility to use PRM in a multiplexed way as an attractive alternative for immunoassays without the use of antibodies or comparable binders.