Abstract
Decoding the role of histone posttranslational modifications (PTMs) is key to understand the fundamental process of epigenetic regulation. This is well studied for PTMs of core histones but not for linker histone H1 in general and its ubiquitylation in particular due to a lack of proper tools. Here, we report on the chemical synthesis of site-specifically mono-ubiquitylated H1.2 and identify its ubiquitin-dependent interactome on a proteome-wide scale. We show that site-specific ubiquitylation of H1 at position K64 modulates interactions with deubiquitylating enzymes and the deacetylase SIRT1. Moreover, it affects H1-dependent chromatosome assembly and phase separation resulting in a more open chromatosome conformation generally associated with a transcriptionally active chromatin state. In summary, we propose that site-specific ubiquitylation plays a general regulatory role for linker histone H1.
Highlights
Decoding the role of histone posttranslational modifications (PTMs) is key to understand the fundamental process of epigenetic regulation
To investigate the effects of site-specific ubiquitylation of H1, we generated three variants containing Plk in the proteins’ three structural domains: the NTD (H1.2 K17Plk), the GD (H1.2 K64Plk), and the CTD (H1.2 K206Plk). These positions had been identified to be ubiquitylated in several previous studies[46,47,48,49,50,51]
The incorporation of Plk was verified by mass spectrometry (MS) and the correct structural fold of the H1.2 KxPlk variants was validated by circular dichroism (CD) spectroscopy (Supplementary Fig. 2a-c)
Summary
Decoding the role of histone posttranslational modifications (PTMs) is key to understand the fundamental process of epigenetic regulation This is well studied for PTMs of core histones but not for linker histone H1 in general and its ubiquitylation in particular due to a lack of proper tools. We show that site-specific ubiquitylation of H1 at position K64 modulates interactions with deubiquitylating enzymes and the deacetylase SIRT1 It affects H1-dependent chromatosome assembly and phase separation resulting in a more open chromatosome conformation generally associated with a transcriptionally active chromatin state. The linker histone H1 binds at the nucleosome entry and exit sites in a dynamic manner to form higher-order chromatin structures. H1 binds dynamically to chromosomes and plays a fundamental role in the formation of higher-order chromatin. Ubiquitylation of H1 was linked to activation of gene expression[22] and antiviral protection[23], and more recently H1 ubiquitylation has been put forward as a histone mark relevant in the response to DNA damage[24,25]
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