Abstract
The fundamental unit of chromatin, the nucleosome, is an intricate structure that requires histone chaperones for assembly. ATAD2 AAA+ ATPases are a family of histone chaperones that regulate nucleosome density and chromatin dynamics. Here, we demonstrate that the fission yeast ATAD2 homolog, Abo1, deposits histone H3–H4 onto DNA in an ATP-hydrolysis-dependent manner by in vitro reconstitution and single-tethered DNA curtain assays. We present cryo-EM structures of an ATAD2 family ATPase to atomic resolution in three different nucleotide states, revealing unique structural features required for histone loading on DNA, and directly visualize the transitions of Abo1 from an asymmetric spiral (ATP-state) to a symmetric ring (ADP- and apo-states) using high-speed atomic force microscopy (HS-AFM). Furthermore, we find that the acidic pore of ATP-Abo1 binds a peptide substrate which is suggestive of a histone tail. Based on these results, we propose a model whereby Abo1 facilitates H3–H4 loading by utilizing ATP.
Highlights
The fundamental unit of chromatin, the nucleosome, is an intricate structure that requires histone chaperones for assembly
We discover a mechanism by which Abo[1] accommodates histone substrates, allowing it to function as a unique energy-dependent histone chaperone
Here we show that Abo[1] directly mediates H3–H4 loading onto DNA, it remains to be determined whether there is truly a difference between species, or whether Abo[1] can function both to promote histone assembly and disassembly depending on the biological context as has been proposed for other ATP-independent histone chaperones such as FACT24–26
Summary
The fundamental unit of chromatin, the nucleosome, is an intricate structure that requires histone chaperones for assembly. ATAD2 AAA+ ATPases are a family of histone chaperones that regulate nucleosome density and chromatin dynamics. We find that the acidic pore of ATP-Abo[1] binds a peptide substrate which is suggestive of a histone tail. Based on these results, we propose a model whereby Abo[1] facilitates H3–H4 loading by utilizing ATP. 1234567890():,; Chromatin is a dynamic structure that undergoes significant structural changes during DNA replication, transcription, and repair. This necessitates the regulated assembly and disassembly of nucleosomes by correct deposition of histones or removal of histones from DNA. Dysfunction of histone chaperones affects genome stability and gene expression, and can result in developmental disorders and cancer[2,3]
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