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XB-ART-45025
J Mol Biol 2012 Jan 20;4153:600-14. doi: 10.1016/j.jmb.2011.11.032.
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The H2A-H2B dimeric kinetic intermediate is stabilized by widespread hydrophobic burial with few fully native interactions.

Guyett PJ , Gloss LM .


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The H2A-H2B histone heterodimer folds via monomeric and dimeric kinetic intermediates. Within ∼5 ms, the H2A and H2B polypeptides associate in a nearly diffusion limited reaction to form a dimeric ensemble, denoted I₂ and I₂*, the latter being a subpopulation characterized by a higher content of nonnative structure (NNS). The I₂ ensemble folds to the native heterodimer, N₂, through an observable, first-order kinetic phase. To determine the regions of structure in the I₂ ensemble, we characterized 26 Ala mutants of buried hydrophobic residues, spanning the three helices of the canonical histone folds of H2A and H2B and the H2B C-terminal helix. All but one targeted residue contributed significantly to the stability of I₂, the transition state and N₂; however, only residues in the hydrophobic core of the dimer interface perturbed the I₂* population. Destabilization of I₂* correlated with slower folding rates, implying that NNS is not a kinetic trap but rather accelerates folding. The pattern of Φ values indicated that residues forming intramolecular interactions in the peripheral helices contributed similar stability to I₂ and N₂, but residues involved in intermolecular interactions in the hydrophobic core are only partially folded in I₂. These findings suggest a dimerize-then-rearrange model. Residues throughout the histone fold contribute to the stability of I₂, but after the rapid dimerization reaction, the hydrophobic core of the dimer interface has few fully native interactions. In the transition state leading to N₂, more native-like interactions are developed and nonnative interactions are rearranged.

???displayArticle.pubmedLink??? 22137897
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Species referenced: Xenopus laevis
Genes referenced: h2ac21 h2bc21

References [+] :
Banks, Equilibrium folding of the core histones: the H3-H4 tetramer is less stable than the H2A-H2B dimer. 2003, Pubmed