Profiling the Trypanosoma cruzi phosphoproteome

Abstract

Protein phosphorylation is a reversible post-translational modification essential for the regulation of several signal transduction pathways and biological processes in the living cell. Therefore, the identification of protein phosphorylation sites is crucial to understand cell signaling control at the molecular level. Based on mass spectrometry, recent studies have reported the large-scale mapping of phosphorylation sites in various eukaryotes and prokaryotes. However, little is known about the impact of phosphorylation in protozoan parasites. To in depth characterize the phosphoproteome of Trypanosoma cruzi, a parasite of the Kinetoplastida class, protein samples from cells at different phases of the metacyclogenesis--differentiation process of the parasites from non-infective epimastigotes to infective metacyclic trypomastigotes--were enriched for phosphopeptides using TiO(2) chromatography and analyzed on an LTQ-Orbitrap mass spectrometer. In total, 1,671 proteins were identified, including 753 phosphoproteins, containing a total of 2,572 phosphorylation sites. The distribution of phosphorylated residues was 2,162 (84.1%) on serine, 384 (14.9%) on threonine and 26 (1.0%) on tyrosine. Here, we also report several consensus phosphorylation sequence motifs and as some of these conserved groups have enriched biological functions, we can infer the regulation by protein kinases of this functions. To our knowledge, our phosphoproteome is the most comprehensive dataset identified until now for Kinetoplastida species. Here we also were able to extract biological information and infer groups of sites phosphorylated by the same protein kinase. To make our data accessible to the scientific community, we uploaded our study to the data repositories PHOSIDA, Proteome Commons and TriTrypDB enabling researchers to access information about the phosphorylation sites identified here.

Figure 1. Kinases with phosphorylated activation loop.

Blue boxes represent the conserved regions. Red line at the bottom represents the activation region, with the non-organized activation loop in between the two conserved regions. The identified phosphorylation sites are highlighted in green.

Figure 2. Sequence windows used to extract phosphorylation motifs.

The sequence represents an example of the phosphorylated region of a protein, showing the backbone structure of the different window sizes used to extract phosphorylation motifs. The red letter represents the phosphorylated residue (always centered), the blue letters were emphasized to show the surrounding amino acids included in each of the window sizes.

Figure 3. Motifs found to have GO terms overrepresented.