Extended string-like binding of the phosphorylated HP1α N-terminal tail to the lysine 9-methylated histone H3 tail

Abstract

The chromodomain of HP1α binds directly to lysine 9-methylated histone H3 (H3K9me). This interaction is enhanced by phosphorylation of serine residues in the N-terminal tail of HP1α by unknown mechanism. Here we show that phosphorylation modulates flexibility of HP1α’s N-terminal tail, which strengthens the interaction with H3. NMR analysis of HP1α’s chromodomain with N-terminal tail reveals that phosphorylation does not change the overall tertiary structure, but apparently reduces the tail dynamics. Small angle X-ray scattering confirms that phosphorylation contributes to extending HP1α’s N-terminal tail. Systematic analysis using deletion mutants and replica exchange molecular dynamics simulations indicate that the phosphorylated serines and following acidic segment behave like an extended string and dynamically bind to H3 basic residues; without phosphorylation, the most N-terminal basic segment of HP1α inhibits interaction of the acidic segment with H3. Thus, the dynamic string-like behavior of HP1α’s N-terminal tail underlies the enhancement in H3 binding due to phosphorylation.

The effect of epigenetic modifications on the secondary structures and possible binding positions of the N-terminal tail of histone H3 in the nucleosome: a computational study

“…The binding positions towards the side of the nucleosome and the observation that the modified lysine side-chains protrude into the solvent with no direct role with in the peptide structure also make it possible for effector proteins to bind. Curiously, the absence of structure in both the active and inactive tail tips is also in accordance with resolved structures of modified H3 tail tips bound by effector proteins, which show a random coil structure for the tail tips [ 73 , 74 ]…”

Single-molecule kinetic analysis of HP1-chromatin binding reveals a dynamic network of histone modification and DNA interactions

“…The reduced DNA interaction propensity of pHP1α resulted in two-fold slower chromatin binding (Figure 6D ) compared to non-phosphorylated HP1α. In contrast, dissociation of pHP1α from chromatin was found to be slowed down as well, with a significant fraction of binding events (10 ± 1%) that decayed with a time constant of τ off,2 = 5.6 ± 0.37 s. Phosphorylation of HP1α thus not only decreases its binding rate by reducing DNA binding, but stabilizes multivalent interactions on chromatin, possibly through conformational changes within the protein ( 23 ) and additional interactions with the H3 N-terminal tail ( 29 , 50 , 56 ).…”

Structural visualization of key steps in nucleosome reorganization by human FACT

“…A 33/112-bp DSB nucleosome, 145-bp nucleosomes (intact, H3_ΔN-tail, and H2B_Δ-Ntail), 112-bp octasomes (intact, H3_ΔN-tail, and H2B_Δ-Ntail), a 112-bp octasome/Mid-pAID complex, a 112-bp octasome/pAID complex, a 112-bp octasome/FACT complex, a 102-bp octasome/Mid-pAID complex, a 102-bp octasome/pAID complex, and a 102-bp octasome/FACT complex were reconstituted from histones, DNAs, and the FACT proteins by the salt dialysis method, and then purified as described previously 29 . The truncated pAID (926–964), pAID (949–985), and SSRP1-pAID (434–514) proteins were expressed in Escherichia coli strain BL21 (DE3) containing the expression plasmid pColdI (pAID) with or without pRSFduet (CK2), as reported previously 46 . Cells were suspended in buffer containing 150 mM NaCl, 20 mM Tris-HCl, pH 8.5, and 1 mM DTT, and lysed by sonication.…”