Research Article

The histone H3-H4 tetramer is a copper reductase enzyme

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Science  03 Jul 2020:
Vol. 369, Issue 6499, pp. 59-64
DOI: 10.1126/science.aba8740

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Enzymatic activity of histones

Eukaryotic histones serve as structural elements to package DNA. However, they contain a copper-binding site for which the biological relevance is unknown. Copper homeostasis is critical for several fundamental eukaryotic processes, including mitochondrial respiration. Attar et al. hypothesized that histones may play a critical role in cellular copper utilization (see the Perspective by Rudolph and Luger). Using a multifaceted approach ranging from in vitro biochemistry to in vivo genetic and molecular analyses, they found that the histone H3-H4 tetramer is an oxidoreductase enzyme that catalyzes reduction of cupric ions, thereby providing biologically usable cuprous ions for various cellular processes. This work opens a new front for chromatin biology, with implications for eukaryotic evolution and human biology and disease.

Science, this issue p. 59; see also p. 33

Abstract

Eukaryotic histone H3-H4 tetramers contain a putative copper (Cu2+) binding site at the H3-H3′ dimerization interface with unknown function. The coincident emergence of eukaryotes with global oxygenation, which challenged cellular copper utilization, raised the possibility that histones may function in cellular copper homeostasis. We report that the recombinant Xenopus laevis H3-H4 tetramer is an oxidoreductase enzyme that binds Cu2+ and catalyzes its reduction to Cu1+ in vitro. Loss- and gain-of-function mutations of the putative active site residues correspondingly altered copper binding and the enzymatic activity, as well as intracellular Cu1+ abundance and copper-dependent mitochondrial respiration and Sod1 function in the yeast Saccharomyces cerevisiae. The histone H3-H4 tetramer, therefore, has a role other than chromatin compaction or epigenetic regulation and generates biousable Cu1+ ions in eukaryotes.

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