HISTONE POST-TRANSLATIONAL MODIFICATIONS IN THE PROTOZOAN PARASITE GIARDIA LAMBLIA

SALUSSO, AGOSTINA; JAQUET SPENSER; DIAZ PEREZ LUCIANO; CIBOROWSKI PAWEL ; ROPOLO, ANDREA SILVANA

SALTA

Congreso; JOINTLV ANNUAL SAIB MEETING AND XIV PABMB CONGRESS; 2019

Histones are very low molecular weight proteins that together with DNA build chromatin in eukaryotic cells. The amino-terminal ends of histones are susceptible to post-translational modifications, which have an impact on chromatin structure and therefore on the regulation of gene expression. At present, it is proposed that all of these modifications on histone tails form an undercover language known as the "histone code", which is read by different proteins and govern chromatin structure and regulate gene expression. In the protozoan parasite Giardia lamblia, epigenetic modifications have begun to be studied in recent years, analyzing histone-modifying enzymes, but so far, the particular modifications of each histone are unknown. The main objective of this work was to obtain the complete map of the post-translational modifications in the histones of Giardia lamblia. For that, we isolated the histones of growing trophozoites and performed mass spectrometry tests using two liquid chromatography and mass spectrometry platforms. We identified different peptides of H2A, H2B, H3, and H4 included in the Giardia histone code. We found modifications preserved in other organisms, such as lysine acetylation, lysine and arginine methylation, threonine and tyrosine phosphorylation and lysine ubiquitination. In turn, we described for the first time the propionylation of amino acids in Giardia trophozoites. Moreover, in the general analysis, we observed that the same amino acid might suffer different types of modifications and depending on the type of that modification, different modifications may appear in close residues, which would indicate that there is an exchange of information (cross talk) in neighboring amino acids. Interestingly, we found arginine methylation although in the Giardia DataBase there are no enzymes described as HRMT (histone-arginine methyltransferase). However, three enzymes were described as possible histone lysine methyltransferases (HMT1, HMT2, and SET2), therefore the presence of methylated arginines indicates that possibly some of the HMTs that modify lysines, could also be modifying arginines. Finally, our work provides the first large-scale characterization of the Giardia histone code, which constitutes an essential initial platform for the development of future research in the field of epigenetics in this parasite.