Post-translational modifications of FDA-approved plasma biomarkers in glioblastoma samples

<div><p>Liquid chromatography-tandem mass spectrometry was used to analyze plasma proteins of volunteers (control) and patients with glioblastoma multiform (GBM). A database search was pre-set with a variable post-translational modification (PTM): phosphorylation, acetylation or ubiquitination. There were no significant differences between the control and the GBM groups regarding the number of protein identifications, sequence coverage or number of PTMs. However, in GBM plasma, we unambiguously observed a decreased fraction in post-translationally modified peptides identified with high quality. The disease-specific PTM patterns were extracted and mapped to the set of FDA-approved plasma protein markers. Decreases of 46% and 24% in the number of acetylated and ubiquitinated peptides, respectively, were observed in the GBM samples. Significance of capturing disease-associated patterns of protein modifications was envisaged.</p></div

Enrichment of plasma Alpha-2-HS-glycoprotein (FETUA_HUMAN, 367 aa) sequence coverage with peptides assembled from MS/MS search for phosphorylated peptides.

<p>Enrichment of plasma Alpha-2-HS-glycoprotein (FETUA_HUMAN, 367 aa) sequence coverage with peptides assembled from MS/MS search for phosphorylated peptides.</p

Sequence coverage for various protein PTMs.

<p>Identification by Mascot of ≥ 3 peptides per protein. The adjusted inverse normalized values are displayed as a violin plot, comparing distributions between control and GBM samples. Horizontal bars indicate the mean (dashed line) and median (solid line) values for each group.</p

Changes in the fractions of PTM peptides of FDA-approved plasma biomarkers in GBM compared to control.

<p>Changes in the fractions of PTM peptides of FDA-approved plasma biomarkers in GBM compared to control.</p

MS/MS spectra of non-modified (A) and phosphomodified (B) peptide DSSPDSAEDVR (2+) of alpha-2-HS-glycoprotein (FETUA_HUMAN) GBM plasma.

<p>Monoisotopic mass of neutral peptide Mr (calc) 1,592.62. Variable modification S7–Phospho (ST) with neutral loss 97.98. [<i>y</i>(10)] in a non-modified peptide was not detected.</p

Number of identified proteins/peptides due to PTM-sensitive MS/MS search for control and GBM plasma samples.

<p>Number of identified proteins/peptides due to PTM-sensitive MS/MS search for control and GBM plasma samples.</p

GBM-negative and GBM-positive patterns’ counted for FDA-approved plasma proteins.

<p>GBM-negative and GBM-positive patterns’ counted for FDA-approved plasma proteins.</p