Abstract
Histone chaperones are a diverse class of proteins that facilitate chromatin assembly. Their ability to stabilize highly abundant histone proteins in the cellular environment prevents non-specific interactions and promotes nucleosome formation, but the various mechanisms for doing so are not well understood. We now focus on the dynamic features of the DAXX histone chaperone that have been elusive from previous structural studies. Using hydrogen/deuterium exchange coupled to mass spectrometry (H/DX-MS), we elucidate the concerted binding-folding of DAXX with histone variants H3.3/H4 and H3.2/H4 and find that high local stability at the variant-specific recognition residues rationalizes its known selectivity for H3.3. We show that the DAXX histone binding domain is largely disordered in solution and that formation of the H3.3/H4/DAXX complex induces folding and dramatic global stabilization of both histone and chaperone. Thus, DAXX uses a novel strategy as a molecular chaperone that paradoxically couples its own folding to substrate recognition and binding. Further, we propose a model for the chromatin assembly reaction it mediates, including a stepwise folding pathway that helps explain the fidelity of DAXX in associating with the H3.3 variant, despite an extensive and nearly identical binding surface on its counterparts, H3.1 and H3.2.
Highlights
Nucleosome assembly is a dynamic multi-step process that is regulated by histone chaperones
The trend for functional specialization in higher eukaryotes is apparent among a subclass of histone chaperones, including DAXX, HIRA and HJURP that selectively bind histone H3 variants H3.3 (DAXX and HIRA) and CENP-A (HJURP) [2,3,4,5,6,7,8,9]
We measure the stability conferred to both the histone substrate complex ([H3.3/H4]2) and the monomeric chaperone on heterotrimer formation, test the degree to which DAXXbinding can induce a stable fold to a partially unfolded H3.3 mutant protein and compare the backbone dynamics of DAXX when bound to its target variant (H3.3) versus when bound to an inappropriate substrate (H3.2). Considering these findings, we propose a model for how selectivity is achieved in the DAXX-mediated nucleosome assembly pathway for the H3.3 variant
Summary
Nucleosome assembly is a dynamic multi-step process that is regulated by histone chaperones Tailored to their highly conserved architectural and regulatory function within the nucleosome, histone protomers outside of the nucleosomal context require a diverse family of proteins to prevent unspecific contacts. These so-called histone chaperones use a variety of structural motifs to contact their cognate histones and seem to have largely nonoverlapping specific functions in histone metabolism and nucleosome assembly in distinct chromosomal loci [1]. The unique structures and binding mechanisms of these histone chaperone complexes are expected to reflect their specific functions and are the subject of current investigation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
