Abstract

Nucleoplasmin is a histone chaperone that consists of a pentameric N-terminal domain and an unstructured C-terminal tail. The pentameric core domain, a doughnut-like structure with a central pore, is only found in the nucleoplasmin family. Here, we report the first structure of a nucleoplasmin-like domain (NPL) from the unrelated Drosophila protein, FKBP39, and we present evidence that this protein associates with chromatin. Furthermore, we show that two other chromatin proteins, Arabidopsis thaliana histone deacetylase type 2 (HD2) and Saccharomyces cerevisiae Fpr4, share the NPL fold and form pentamers, or a dimer of pentamers in the case of HD2. Thus, we propose a new family of proteins that share the pentameric nucleoplasmin-like NPL domain and are found in protists, fungi, plants and animals.

Highlights

  • We show that two other chromatin proteins, Arabidopsis thaliana histone deacetylase type 2 (HD2) and Saccharomyces cerevisiae Fpr4, share the nucleoplasmin-like domain (NPL) fold and form pentamers, or a dimer of pentamers in the case of HD2

  • This can be observed in the sequence alignment (Fig. 2) where only the hydrophobic character of some residues and the position of the β-strands are preserved between Xenopus nucleoplasmin and all the other proteins

  • Because we found by mass spectrometry that the truncated N-terminal construct can form oligomers with endogenous full-length FKBP39 through the NPL, we can only conclude at present that it is not the C-terminal half by itself that is responsible for the interactions observed with the full-length protein

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Summary

Introduction

Nucleoplasmin (NUP) provides a longlasting store of histones H2A/H2B in Xenopus eggs, which is sufficient for a dozen or so rounds of DNA replication after fertilisation. It is involved in the de-condensation of sperm chromatin Nucleoplasmin's many phosphorylated residues, as well as some acidic loops, seem to play a part in binding positively charged histones. Poly-glutamate (mimicking the C-terminal tail of nucleoplasmin) has been found to de-condense sperm chromatin, presumably through binding positively charged histones, albeit less efficiently than nucleoplasmin [2,3,4]. Its structure was solved [5] revealing a homo-pentamer, prompting the question of how a molecule with 5-fold symmetry might interact with histone complexes, which have even-numbered (http://creativecommons.org/licenses/by/4.0/)

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