Chromatin Proteomics Reveals Variable Histone Modifications during the Life Cycle of Trypanosoma cruzi

Histones are well-conserved
proteins that form the basic structure
of chromatin in eukaryotes and undergo several post-translational
modifications, which are important for the control of transcription,
replication, DNA damage repair, and chromosome condensation. In early
branched organisms, histones are less conserved and appear to contain
alternative sites for modifications, which could reveal evolutionary
unique functions of histone modifications in gene expression and other
chromatin-based processes. Here, by using high-resolution mass spectrometry,
we identified and quantified histone post-translational modifications
in two life cycle stages of Trypanosoma cruzi, the protozoan parasite that causes Chagas disease. We detected
44 new modifications, namely: 18 acetylations, seven monomethylations,
seven dimethylations, seven trimethylations, and four phosphorylations.
We found that replicative (epimastigote stage) contains more histone
modifications than nonreplicative and infective parasites (trypomastigote
stage). Acetylations of lysines at the C-terminus of histone H2A and
methylations of lysine 23 of histone H3 were found to be enriched
in trypomastigotes. In contrast, phosphorylation in serine 23 of H2B
and methylations of lysine 76 of histone H3 predominates in proliferative
states. The presence of one or two methylations in the lysine 76 was
found in cells undergoing mitosis and cytokinesis, typical of proliferating
parasites. Our findings provide new insights into the role of histone
modifications related to the control of gene expression and cell-cycle
regulation in an early divergent organism.

组蛋白是一类高度保守的蛋白质，它们构成了真核生物染色质的基本结构，并经历多种翻译后修饰，这些修饰对于转录调控、复制、DNA损伤修复以及染色体凝缩等过程至关重要。在早期分支生物中，组蛋白的保守性较低，并似乎含有修饰的替代位点，这可能会揭示组蛋白修饰在基因表达和其他基于染色质的过程中的进化独特功能。本研究中，我们利用高分辨率质谱技术，在克氏锥虫（引起恰加斯病的原生动物寄生虫）的两个生命周期阶段中鉴定并量化了组蛋白的翻译后修饰。我们发现了44种新的修饰，包括：18种乙酰化、7种单甲基化、7种二甲基化、7种三甲基化和4种磷酸化。我们发现，复制阶段（上皮型滋养体阶段）的组蛋白修饰数量多于非复制和侵袭性寄生虫（前鞭毛体阶段）。组蛋白H2A的C端赖氨酸的乙酰化和组蛋白H3赖氨酸23位的甲基化在鞭毛体中被发现富集。相比之下，H2B的丝氨酸23位的磷酸化和组蛋白H3赖氨酸76位的甲基化在增殖状态下占主导地位。在经历有丝分裂和细胞分裂的细胞中，赖氨酸76位存在一个或两个甲基化，这是增殖性寄生虫的典型特征。我们的发现为早期分歧生物中与基因表达调控和细胞周期调节相关的组蛋白修饰作用提供了新的见解。