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A helix-turn motif in the C-terminal domain of histone H1

Published online by Cambridge University Press:  01 April 2000

ROGER VILA
Affiliation:
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad Autónoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
IMMA PONTE
Affiliation:
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad Autónoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
M. ANGELES JIMÉNEZ
Affiliation:
Instituto de Estructura de la Materia, CSIC, Serrano, 119 28006 Madrid, Spain
MANUEL RICO
Affiliation:
Instituto de Estructura de la Materia, CSIC, Serrano, 119 28006 Madrid, Spain
PEDRO SUAU
Affiliation:
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad Autónoma de Barcelona, 08193 Bellaterra, Barcelona, Spain
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Abstract

The structural study of peptides belonging to the terminal domains of histone H1 can be considered as a step toward the understanding of the function of H1 in chromatin. The conformational properties of the peptide Ac-EPKRSVAFKKTKKEVKKVATPKK (CH-1), which belongs to the C-terminal domain of histone H1° (residues 99–121) and is adjacent to the central globular domain of the protein, were examined by means of 1H-NMR and circular dichroism. In aqueous solution, CH-1 behaved as a mainly unstructured peptide, although turn-like conformations in rapid equilibrium with the unfolded state could be present. Addition of trifluoroethanol resulted in a substantial increase of the helical content. The helical limits, as indicated by (i, i + 3) nuclear Overhauser effect (NOE) cross correlations and significant up-field conformational shifts of the Cα protons, span from Pro100 to Val116, with Glu99 and Ala117 as N- and C-caps. A structure calculation performed on the basis of distance constraints derived from NOE cross peaks in 90% trifluoroethanol confirmed the helical structure of this region. The helical region has a marked amphipathic character, due to the location of all positively charged residues on one face of the helix and all the hydrophobic residues on the opposite face. The peptide has a TPKK motif at the C-terminus, following the α-helical region. The observed NOE connectivities suggest that the TPKK sequence adopts a type (I) β-turn conformation, a σ-turn conformation or a combination of both, in fast equilibrium with unfolded states. Sequences of the kind (S/T)P(K/R)(K/R) have been proposed as DNA binding motifs. The CH-1 peptide, thus, combines a positively charged amphipathic helix and a turn as potential DNA-binding motifs.

Type
Research Article
Copyright
© 2000 The Protein Society

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