Comprehensive interactome profiling of the human Hsp70 network highlights functional differentiation of J domains.

Hsp70s comprise a deeply conserved chaperone family that has a central role in maintaining protein homeostasis. In humans, Hsp70 client specificity is provided by 49 different co-factors known as J domain proteins (JDPs). However, the cellular function and client specificity of JDPs have largely remained elusive. We have combined affinity purification-mass spectrometry (AP-MS) and proximity-dependent biotinylation (BioID) to characterize the interactome of all human JDPs and Hsp70s. The resulting network suggests specific functions for many uncharacterized JDPs, and we establish a role of conserved JDPs DNAJC9 and DNAJC27 in histone chaperoning and ciliogenesis, respectively. Unexpectedly, we find that the J domain of DNAJC27 but not of other JDPs can fully replace the function of endogenous DNAJC27, suggesting a previously unappreciated role for J domains themselves in JDP specificity. More broadly, our work expands the role of the Hsp70-regulated proteostasis network and provides a platform for further discovery of JDP-dependent functions. [Display omitted] • Protein-protein and proximity interaction networks of all human JDPs and Hsp70s • DNAJC9 is a histone H3/H4-specific chaperone essential for cell proliferation • DNAJC27 is a novel regulator of ciliogenesis together with its interactor FAM184A • J domains are not interchangeable; they can have unique roles beyond binding Hsp70 Piette and colleagues used AP-MS and BioID to systematically characterize the interaction network of all human J domain proteins (JDPs) and Hsp70s. They discovered roles for specific JDPs in RNA splicing, histone chaperoning, and ciliogenesis. They also uncovered an unexpected role for the J domain itself in determining JDP functional specificity. [ABSTRACT FROM AUTHOR]