Begona Barroso

Chemical labeling and enrichment of nitrotyrosine-containing peptides

Protein tyrosine nitration (PTN) is a post-translational modification of proteins associated with a number of inflammatory diseases. While PTN is rather selective (not all proteins are modified and within a protein, only certain tyrosines are subject to nitration), no consensus sequence has been identified. Since PTN is a low-abundance post-translational modification, it is necessary to enrich modified proteins and/or to detect them with high selectivity and sensitivity. Until now this has been mostly accomplished with anti-nitrotyrosine antibodies in combination with two-dimensional gel electrophoresis and mass spectrometry. We propose a chemical labeling approach designed to allow enrichment of tyrosine-nitrated peptides independent of the sequence context, which is a potential shortcoming of antibody-based approaches. In this procedure, all amines are blocked by acetylation followed by conversion of nitrotyrosine to aminotyrosine and biotinylation of aminotyrosine. The entire reaction sequence is performed in a single buffer with no need for sample cleanup or pH changes thereby reducing sample loss. Free biotin is subsequently removed with a strong cation exchanger, the labeled peptides are enriched on an immobilized avidin column and the enriched peptides analyzed by LC-MS/MS. As a proof of concept, this method was successfully applied to the enrichment of tyrosine-nitrated angiotensin II in a tryptic digest of bovine serum albumin (BSA). The approach presented here is well adapted to peptide analysis, for instance in shotgun proteomics.

Recent developments in proteoglycan purification and analysis

Proteoglycans are ubiquitous biomolecules in the body located in the extracellular matrix, on the cell surface and also within the cells. They contain at least one glycosaminoglycan (GAG) chain covalently attached to a core protein and may also present N- or O-linked glycans. The high structural diversity and distribution relate to the various biological functions of proteoglycans. In recent years, new members have enlarged the proteoglycan family and advances in molecular biology and glycobiology contributed to elucidate more of the biological functions of proteoglycans. In order to study the structure of a proteoglycan molecule and relate it to its function (or dysfunction), its isolation and purification from cell culture or tissue extracts is necessary. Next to the widely used anion exchange chromatographic methods, techniques based on lectin affinity chromatography have created new possibilities to increase the degree of purity. Introduction of electrospray ionization (ESI) and matrix-assisted laser desorption-ionization (MALDI) sources, together with tandem mass spectrometry (MS/MS or MSn), mark a further important step towards the structural analysis of glycosaminoglycans. The aim of this review is to present the most recent advances in proteoglycan purification and analysis.

Adenosine receptors in COPD and asymptomatic smokers: effects of smoking cessation

Our group has shown that 1-year smoking cessation persisted or increased airway inflammation in chronic obstructive pulmonary disease (COPD). We compared adenosine and adenosine receptor (AR) expression in COPD and asymptomatic smokers (AS) before and after 1-year smoking cessation. Sputum cytospins and bronchial biopsies of (ex)smoking COPD patients and AS were studied for A1R, A2AR, A2BR, and A3R expression. Adenosine and inflammatory mediators were measured in sputum supernatants. At baseline, COPD patients had lower levels of adenosine and higher levels of vascular endothelial growth factor in sputum than AS. Smoking cessation induced significantly different effects in COPD than in AS, i.e. an increase in percentages of A3R expressing neutrophils and A1R expressing macrophages in COPD as increase in adenosine and monocyte chemoattractant protein-1 levels in sputum. Adenosine-related effector mechanisms may contribute to the persistence and progression of airway inflammation in COPD following 1-year smoking cessation.