DNAJC9 integrates heat shock molecular chaperones into the histone chaperone network

Summary From biosynthesis to assembly into nucleosomes, histones are handed through a cascade of histone chaperones, which shield histones from non-specific interactions. Whether mechanisms exist to safeguard the histone fold during histone chaperone handover events or to release trapped intermediates is unclear. Using structure-guided and functional proteomics, we identify and characterize a histone chaperone function of DNAJC9, a heat shock co-chaperone that promotes HSP70-mediated catalysis. We elucidate the structure of DNAJC9, in a histone H3-H4 co-chaperone complex with MCM2, revealing how this dual histone and heat shock co-chaperone binds histone substrates. We show that DNAJC9 recruits HSP70-type enzymes via its J domain to fold histone H3-H4 substrates: upstream in the histone supply chain, during replication- and transcription-coupled nucleosome assembly, and to clean up spurious interactions. With its dual functionality, DNAJC9 integrates ATP-resourced protein folding into the histone supply pathway to resolve aberrant intermediates throughout the dynamic lives of histones.
Graphical abstract
Highlights • DNAJC9 is a dual histone chaperone and heat shock co-chaperone • Crystal structure reveals the binding mode of DNAJC9 with H3-H4 dimers • DNAJC9 recruits HSP70 enzymes to guard histone structural integrity • ATP-dependent protein folding is integral to histone chaperone biology
Hammond et al. identified and characterized a histone chaperone functionality in the heat shock co-chaperone DNAJC9. DNAJC9 directs molecular chaperones to histone substrates, facilitating their supply to and transactions within chromatin. This study highlights that histone chaperones and molecular chaperones combine to fully protect histone proteins on route to chromatin.