De-novo discovery of posttranslational histone modifications in Schistosoma mansoni stages

Schistosoma mansoni, a parasitic flatworm, causes schistosomiasis. Approximately 250 million people are infected and require drug treatment. Currently, Praziquantel is the only available drug, but it is ineffective against early infective stages. The development of new drugs is urgently needed. Posttranslational modifications (PTM) of histones are crucial for the parasite's life cycle, making them a suitable drug target. However, many of these modifications are conserved between humans and parasites, posing a risk of severe side effects for patients. Identifying schistosome-specific histone PTMs is essential. We employed a bottom-up mass spectrometry method combining first-time Data Independent Acquisition (DIA) and Data Dependent Acquisition (DDA) to quantify histone peptides and assess histone proteins across three S. mansoni stages. We selected 18 main post-translational modifications (PTMs) for peptide searches and identified 150 PTMs across peptides from H3, H4, H1/H5, and H2A of S. mansoni. We further refined with more stringency, given the complexity of the mass spectrometry data and our commitment to reliable data generation, we focused on quantifying H3 PTMs,which are well characterized in other species. For histone H3 PTMs, we identified peptides with high abundance and confidence: K27(1-methyl1-methyl)SAPATGGVK, K27(Dimethyl)SAPATGGVK, K9(acetyl)STGGK, and K9(Dimethyl)STGGK. Notably, both K27(Dimethyl)SAPATGGVK and K9(acetyl)STGGK showed higher abundance in schistosomula. Furthermore, we observed a positive correlation between the expression of the gene Smp_053140 and the abundance of the peptide K9(acetyl)STGGK in 3-day schistosomula. We then knocked down this gene, which affected schistosomula morphology, highlighting the significance of histone posttranslational modification and histone-modifying enzymes in S. mansoni development.