title: Chaperone Nap1 shields histone surfaces used in a nucleosome and can put H2A-H2B in an unconventional tetrameric form.
abstract: The histone H2A-H2B heterodimer is an integral component of the nucleosome. The cellular localization and deposition of H2A-H2B into chromatin is regulated by numerous factors, including histone chaperones such as nucleosome assembly protein 1 (Nap1). We use hydrogen-deuterium exchange coupled to mass spectrometry to characterize H2A-H2B and Nap1. Unexpectedly, we find that at low ionic strength, the α helices in H2A-H2B are frequently sampling partially disordered conformations and that binding to Nap1 reduces this conformational sampling. We identify the interaction surface between H2A-H2B and Nap1 and confirm its relevance both in vitro and in vivo. We show that two copies of H2A-H2B bound to a Nap1 homodimer form a tetramer with contacts between H2B chains similar to those in the four-helix bundle structural motif. The organization of the complex reveals that Nap1 competes with histone-DNA and interhistone interactions observed in the nucleosome, thereby regulating the availability of histones for chromatin assembly.
authors: Howard Hughes Medical Institute, Colorado State University, Fort Collins, CO 80523, USA. Electronic address: sheena.darcy@colostate.edu.
authors: Sheena
authors: S
authors: D'Arcy
authors: Kyle W
authors: KW
authors: Martin
authors: Tanya
authors: T
authors: Panchenko
authors: Xu
authors: X
authors: Chen
authors: Serge
authors: S
authors: Bergeron
authors: Laurie A
authors: LA
authors: Stargell
authors: Ben E
authors: BE
authors: Black
authors: Karolin
authors: K
authors: Luger
mesh_terms: D001665:Binding Sites; D042002:Chromatin Assembly and Disassembly; D004271:DNA, Fungal / Q000378:metabolism; D041961:Deuterium Exchange Measurement; D056488:Histone Chaperones; D006657:Histones / Q000737:chemistry / Q000378:metabolism*; D056490:Nucleosome Assembly Protein 1 / Q000235:genetics / Q000378:metabolism*; D009707:Nucleosomes; D009994:Osmolar Concentration; D011487:Protein Conformation; D017510:Protein Folding; D055503:Protein Multimerization; D055550:Protein Stability; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D012996:Solutions
chemical_list: D004271:DNA, Fungal; D056488:Histone Chaperones; D006657:Histones; C533556:NAP1 protein, S cerevisiae; D056490:Nucleosome Assembly Protein 1; D009707:Nucleosomes; D029701:Saccharomyces cerevisiae Proteins; D012996:Solutions
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