Abstract
Histone H1 is one of the proteins that participate in chromatin condensation. This protein has a three domain structure: a globular central region and two N- and C-terminal tails. These tail domains are hydrophilic and basic, very rich in lysine, alanine and proline.Using circular dichroism (CD), double magnetic proton nuclear magnetic resonance (2D-NMR) and infrared spectroscopy (FTIR), we have studied the structure of peptides from the N- and C-terminal domains of H1º and H1e histone subtypes in several conditions: in aqueous solution, in the presence of 2,2,2-trifluoroethanol (TFE) and in the presence of DNA.
The peptides studied are: NH-1, of 20 residues, which corresponds to all the N-terminal domain of histone H1º, identical for mouse and rat; and NH-2, corresponding to the residues 8-30 of the same protein. CH-1 corresponds to the residues 99-121, included in the histone H1º C-terminal domain. NHe-1 corresponds to the residues 15-36 of the mouse histone H1e N-terminal domain.
The CD and proton 2D-NMR studies show that none of the studied histone H1 peptides present stable secondary structure in aqueous solution. In 90% TFE the four peptides acquire a substantial secondary structure percentage, specially a-helix.
In these conditions, NHe-1 become structured in two amphipathic a-helices separated by two glycines. This glycine doublet constitutes a flexible zone that confers a high freedom of movements to the helices.
The N-terminal domain of histone H1º, according to our results with NH-1 and NH-2 peptides in 90% TFE, remains unstructured in its N-terminal half, and from the residue 11 to the 23 it is structured in an a-helix.
CH-1 is structured in an amphipathic helix from the residue 100 to the 116. The first four residues seem to form a 310 helix and the rest an a-helix. The TPKK motif, localized at the C-terminal end of the peptide forms a b/s turn.
We have also studied the peptides NH-1, NH-2 and CH-1 by FTIR spectroscopy. In aqueous solution the amide I' of the three peptides shows a main component at 1641 cm-1 characteristic of an unstructured peptide. In 90% TFE the helix and turn percentages are similar to that of the NMR results. We have used this technique to study the structure of the peptides when bound to mouse genomic DNA and repetitive DNAs like poly[dA-dT]·poly[dA-dT]. There are no important differences between the different DNAs used. Upon interaction with the DNA, the peptides become structured in a-helix in percentages very similar to that observed in 90% TFE. In the spectra of CH-1 / DNA complexes, components attributed to b/s turn and 310 helix also appear.
In conclusion, the DNA induces secondary structure in regions of the N- and C-terminal domains of histone H1, mainly a-helices, 310 helices and turns. The TFE also stabilizes these structures and permits their study at high resolution.
| Date of Award | 13 Jul 2001 |
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| Original language | Catalan |
| Supervisor | Inmaculada Ponte Marull (Director) & Pedro Suau León (Director) |