Induction of Secondary Structure in a COOH-terminal Peptide of Histone H1 by Interaction with the DNA

Abstract

We have studied the conformation of the peptide Ac-EPKRSVAFKKTKKEVKKVATPKK (CH-1), free in solution and bound to the DNA, by Fourier-transform infrared spectroscopy. The peptide belongs to the COOH-terminal domain of histone H1 0 (residues 99 -121) and is adjacent to the central globular domain of the protein. In aqueous (D 2 O) solution the amide I is dominated by component bands at 1643 cm ؊1 and 1662 cm ؊1 , which have been assigned to random coil conformations and turns, respectively. In accordance with previous NMR results, the latter component has been interpreted as arising in turn-like conformations in rapid equilibrium with unfolded states. The peptide becomes fully structured either in 90% trifluoroethanol (TFE) solution or upon interaction with the DNA. In these conditions, the contributions of turn (1662 cm ؊1 ) and random coil components virtually disappear. In TFE, the spectrum is dominated by the ␣-helical component (1654 cm ؊1 ). The band at 1662 cm ؊1 shifts to 1670 cm ؊1 , and has been assigned to the COOH-terminal TPKK motif in a more stable turn conformation. A band at 1637 cm ؊1 , also present in TFE, has been assigned to 3 10 helical structure. The amide I band of the complexes with the DNA retains the components that were attributed to 3 10 helix and the TPKK turn. In the complexes with the DNA, the ␣-helical component observed in TFE splits into two components at 1657 cm ؊1 and 1647 cm ؊1 . Both components are inside the spectral region of ␣-helical structures. Our results support the presence of inducible helical and turn elements, both sharing the character of DNA-binding motifs.

Histone H1 and chromatin interactions in human fibroblast nuclei after H1 depletion and reconstitution with H1 subfractions

“…Solubilized linker histones change their tertiary structure, and the charged tails obtain a random coil conformation (72). The final structure of linker histones in vivo is probably achieved only after binding to chromatin (73), and it may not be possible to retrieve completely this structure after reconstitution in vitro.…”

DNA-induced α-Helical Structure in the NH2-terminal Domain of Histone H1

“…However, the COOH-terminal domains of several H1 subtypes acquire variable amounts of ␣-helical structure in the presence of TFE and other secondary structure stabilizers (2). The presence of a inducible helix-turn motif in the COOH-terminal domain of histone H1°h as been demonstrated by NMR and FTIR spectroscopy (3,5). The structure of the NH 2 -terminal domain had not been addressed before, either in solution or in the complexes with the DNA.…”

“…Samples were measured in 10 mM HEPES, pH 7.0, plus either 10 or 70 mM NaCl. Data treatment and band decomposition of the original amide IЈ have been described previously (3,29). The DNA contribution to the spectra of the complexes of the NH-1 and NH-2 peptides with mouse DNA and alternating poly(dAdT)⅐poly(dA-dT) was subtracted according to Vila et al (3).…”

“…particular residues are in helical conformation, but, because coulombic interactions between basic residues and DNA phosphates promote helical compaction in model and natural peptides (3,37,38), it is likely that the minimal region with helical structure in NH-2 is that containing the basic cluster, between Lys 11 and Lys 20 , although, as in TFE, the helical structure could extend to Asp 23 . Significant as they are, the percentages of ␣-helix in the complexes are, nevertheless, indicative of the presence of alternative modes of binding.…”

“…The COOH-terminal domain acquires, however, a substantial amount of ␣-helix in the presence of secondary structure inducers such as TFE 1 and NaClO 4 (2), suggesting that binding to DNA could stabilize helical segments in the COOH-terminal domain. It has been shown previously by FTIR spectroscopy that a COOH-terminal peptide of histone H1°becomes fully structured upon interaction with the DNA (3). The structures of a turn and of a helix-turn motif belonging to the COOH-terminal domain have been determined by high resolution NMR in the presence of helix stabilizers (4,5).…”