A Quantitative Characterization of Nucleoplasmin/Histone Complexes Reveals Chaperone Versatility.

Noelia Fernández-Rivero,Aitor Franco,Edurne Alonso,Adelina Prado,Arturo Muga,Adrian Velázquez-Campoy

doi:10.1038/srep32114

Noelia Fernández-Rivero, Aitor Franco + Show 4 more

Open Access

https://doi.org/10.1038/srep32114

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Abstract

Nucleoplasmin (NP) is an abundant histone chaperone in vertebrate oocytes and embryos involved in storing and releasing maternal histones to establish and maintain the zygotic epigenome. NP has been considered a H2A–H2B histone chaperone, and recently it has been shown that it can also interact with H3-H4. However, its interaction with different types of histones has not been quantitatively studied so far. We show here that NP binds H2A–H2B, H3-H4 and linker histones with Kd values in the subnanomolar range, forming different complexes. Post-translational modifications of NP regulate exposure of the polyGlu tract at the disordered distal face of the protein and induce an increase in chaperone affinity for all histones. The relative affinity of NP for H2A–H2B and linker histones and the fact that they interact with the distal face of the chaperone could explain their competition for chaperone binding, a relevant process in NP-mediated sperm chromatin remodelling during fertilization. Our data show that NP binds H3-H4 tetramers in a nucleosomal conformation and dimers, transferring them to DNA to form disomes and tetrasomes. This finding might be relevant to elucidate the role of NP in chromatin disassembly and assembly during replication and transcription.

Highlights

Xenopus laevis early embryogenesis is a process characterized by rapid cell division and transcriptional quiescence that depends on parental stored proteins, including histones[1]
The intersection of the linear phase with the plateau gives the molar ratio at which pentameric egg NP (eNP), Oocyte NP (oNP), rNPΔ150–200, and recombinant NP (rNP) are saturated with H2A–H2BT112C. (C) Fluorescence competition assays in which complexes of eNP (0.1 nM)/
Members of the second class bind both core histones with different affinities, as found for CAF-1 that displays an affinity for H3-H4 20-fold higher than for H2A–H2B36

Summary

Introduction

Xenopus laevis early embryogenesis is a process characterized by rapid cell division and transcriptional quiescence that depends on parental stored proteins, including histones[1] Histone chaperones bind these basic ligands to store or escort them to their final destinations[2], and to modulate the post-translational modifications that regulate their chromatin remodelling activity[3,4,5,6]. The mechanism by which PTMs modulate NP affinity for histones most likely involves exposure of the polyGlu (A2) tract, as deletion of the last 50 residues of the C-terminal domain restores the affinity of the recombinant protein to values similar to those of natural NPs. We find that NP binds both association states of H3-H4, and that the chaperone-bound tetramer adopts a nucleosomal conformation that can be transferred to DNA. The intersection of the linear phase with the plateau gives the molar ratio at which pentameric eNP (filled circles), oNP (empty circles), rNPΔ150–200 (gray squares), and rNP (filled diamonds) are saturated with H2A–H2BT112C. (C) Fluorescence competition assays in which complexes of eNP (0.1 nM)/

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