Catalytic activation of histone acetyltransferase Rtt109 by a histone chaperone

Department of Biomolecular Chemistry, School of Medicine and Public Health, University of Wisconsin, 1300 University Avenue, Madison, WI 53706, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 11/2010; 107(47):20275-80. DOI: 10.1073/pnas.1009860107
Source: PubMed

ABSTRACT Most histone acetyltransferases (HATs) function as multisubunit complexes in which accessory proteins regulate substrate specificity and catalytic efficiency. Rtt109 is a particularly interesting example of a HAT whose specificity and catalytic activity require association with either of two histone chaperones, Vps75 or Asf1. Here, we utilize biochemical, structural, and genetic analyses to provide the detailed molecular mechanism for activation of a HAT (Rtt109) by its activating subunit Vps75. The rate-determining step of the activated complex is the transfer of the acetyl group from acetyl CoA to the acceptor lysine residue. Vps75 stimulates catalysis (> 250-fold), not by contributing a catalytic base, but by stabilizing the catalytically active conformation of Rtt109. To provide structural insight into the functional complex, we produced a molecular model of Rtt109-Vps75 based on X-ray diffraction of crystals of the complex. This model reveals distinct negative electrostatic surfaces on an Rtt109 molecule that interface with complementary electropositive ends of a symmetrical Vps75 dimer. Rtt109 variants with interface point substitutions lack the ability to be fully activated by Vps75, and one such variant displayed impaired Vps75-dependent histone acetylation functions in yeast, yet these variants showed no adverse effect on Asf1-dependent Rtt109 activities in vitro and in vivo. Finally, we provide evidence for a molecular model in which a 12 complex of Rtt109-Vps75 acetylates a heterodimer of H3-H4. The activation mechanism of Rtt109-Vps75 provides a valuable framework for understanding the molecular regulation of HATs within multisubunit complexes.

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Available from: Erin Kolonko, Sep 28, 2015
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    • "In Saccharomyces cerevisiae, the transfer of the acetyl group to H3K56 is catalysed by HAT Rtt109 in complex with the H3-H4 dimer (Fillingham et al., 2008; Kolonko et al., 2010). Because of the lack of Rtt109 "
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    ABSTRACT: Posttranslational modifications of histones belong to epigenetic mechanisms that regulate gene expression by chromatin structure changes. Generally, histone acetylation reduces its positive charge and consequently weakens the stability of the nucleosome. Acetylation of lysine 56 on histone H3 is implicated in the processes associated with loosened chromatin structure. H3K56ac is a mark for histones with high nucleosome turnover in the nuclear processes such as gene transcription, DNA replication and reparation in yeasts. During evolution, the main H3K56ac regulatory pathway was lost and the level of H3K56ac remained very low in mammalian cells. Moreover, the function of this modification still remains unclear. In this minireview, we summarize the recent knowledge of the ambiguous role of H3K56ac in mammalian embryonic stem cells.
    Folia biologica 11/2014; 60 Suppl 1:71-5. · 1.00 Impact Factor
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    • "In a cellular context, a proportion of Vps75 is found stably associated with the histone acetyltransferase Rtt109. Interestingly, Rtt109 has been observed to form ring-shaped complexes with Vps75 (10,18,19). However, there appears to be some plasticity in the interface between Vps75 and Rtt109 as both 2:1 and 2:2 Vps75:Rtt109 complexes have been reported. "
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    ABSTRACT: NAP-1 fold histone chaperones play an important role in escorting histones to and from sites of nucleosome assembly and disassembly. The two NAP-1 fold histone chaperones in budding yeast, Vps75 and Nap1, have previously been crystalized in a characteristic homodimeric conformation. In this study, a combination of small angle X-ray scattering, multi angle light scattering and pulsed electron–electron double resonance approaches were used to show that both Vps75 and Nap1 adopt ring-shaped tetrameric conformations in solution. This suggests that the formation of homotetramers is a common feature of NAP-1 fold histone chaperones. The tetramerisation of NAP-1 fold histone chaperones may act to shield acidic surfaces in the absence of histone cargo thus providing a ‘self-chaperoning’ type mechanism.
    Nucleic Acids Research 03/2014; 42(9). DOI:10.1093/nar/gku232 · 9.11 Impact Factor
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    • "By contrast, early characterization of Vps75 demonstrated that this chaperone can bind tetrameric (H3-H4) 2 in vitro (Selth and Svejstrup, 2007). This observation was recently confirmed by structural and biophysical analyses (Bowman et al., 2011; Tang et al., 2011), but it has also been disputed (Kolonko et al., 2010). While this disagreement remains to be rectified, it appears that at least some chaperones are capable of transporting tetrameric histones. "
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    ABSTRACT: The many factors that control chromatin biology play key roles in essential nuclear functions like transcription, DNA damage response and repair, recombination, and replication and are critical for proper cell-cycle progression, stem cell renewal, differentiation, and development. These players belong to four broad classes: histone modifiers, chromatin remodelers, histone variants, and histone chaperones. A large number of studies have established the existence of an intricate functional crosstalk between the different factors, not only within a single class but also between different classes. In light of this, while many recent reviews have focused on structure and functions of histone chaperones, the current text highlights novel and striking links that have been established between these proteins and posttranslational modifications of histones and discusses the functional consequences of this crosstalk. These findings feed a current hot question of how cell memory may be maintained through epigenetic mechanisms involving histone chaperones.
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