Abstract: Post-translational modifications (PTMs) greatly expand proteome complexity and can dynamically tune protein function. Already during their synthesis, proteins are co-translationally processed and N-α-acetylated at their N-terminus. After their synthesis, protein sidechains can be decorated by various forms of PTMs by enzymes or occur non-enzymatic. For instance, protein cysteine thiols are susceptible to oxidative modifications induced by various electrophilic reactive oxygen/nitrogen/sulfur species that can impact protein function.

In the first part of my seminar, I will describe a systemic study of alternative translation initiation sites in Arabidopsis thaliana. By complementary ribosome profiling and N-terminal proteomics, we identified approximately 90 of N-terminal proteoforms shaped by alternative translation initiation – likely providing a mechanism to target protein copies to distinct subcellular locations. Moreover, using an isotopic labeling strategy, we quantify the degree of acetylation of cytosolic protein N-termini in but also of chloroplastic N-termini that can be N-α-acetylated after transit peptide removal. In the second part of my seminar, I will describe a different isotopic labeling strategy for simultaneous monitoring of the degree of cysteine oxidation and protein abundance. Relying on the high reproducibility and accuracy of data-independent acquisition, we obtain comprehensive quantitation of cysteine oxidation during physiologically relevant conditions in plants.

Biography: Patrick Willems obtained his PhD at Ghent University (Belgium) under the joint supervision of Prof. Frank Van Breusegem (VIB-UGent Center for Plant Systems Biology) and Prof. Kris Gevaert (VIB-UGent Center for Medical Biotechnology) studying oxidative stress signaling at various -OMICS layers in plants. After his PhD, he started discovering (un)annotated proteins in Salmonella enterica in the Van Damme lab (Department of Microbiology, Ghent University) with state-of-the-art mass spectrometry techniques. Patrick is now continuing as a postdoctoral researcher supported by a Belgian national grant in the Van Breusegem and Gevaert labs focusing on (oxidative) post-translational modifications in plants during abiotic stress.