Macromolecular crowding induces a molten globule state in the C-terminal domain of histone H1.
We studied the secondary structure of the C-terminal domains of the histone H1 subtypes H1 degrees (C-H1 degrees ) and H1t (C-H1t) in the presence of macromolecular crowding agents (Ficoll 70 and PEG 6000) by IR spectroscopy. The carboxyl-terminal domain has little structure in aqueous solution but became extensively folded in the presence of crowding agents. In 30% PEG, C-H1 degrees contained 19% alpha-helix, 28% beta-sheet, 16% turns, and 31% open loops. Similar proportions were observed in 30% Ficoll 70 and for C-H1t in both crowding agents. The proportions of secondary structure motifs were comparable to those of the DNA-bound domain. Kratky plots of the small-angle x-ray scattering showed that in crowding agents the C-terminus had the compaction of a globular state. Progressive dissipation of the secondary structure and a linear increase in partial heat capacity with temperature together with increased binding of ANS indicated that the C-terminus is not cooperatively folded in crowded conditions. Native-like secondary structure and compactness in absence of folding cooperativity indicate that the C-terminus in crowding agents is in a molten globule state. Folding of the C-terminus in crowded conditions may increase the rate of the transition toward the DNA-bound state and facilitate H1 diffusion inside cell nuclei.
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Alicia
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Departamento de Bioquímica y Biología Molecular, Facultad de Biociencias, Universidad Autónoma de Barcelona, 08193 Bellaterra, Barcelona, Spain.
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D000817:Anilino Naphthalenesulfonates; D001665:Binding Sites; D055592:Biophysical Phenomena; D001703:Biophysics; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D005456:Fluorescent Dyes; D006657:Histones / Q000737:chemistry*; D046912:Multiprotein Complexes; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D012542:Scattering, Radiation; D013050:Spectrometry, Fluorescence; D017550:Spectroscopy, Fourier Transform Infrared; D013816:Thermodynamics; D014965:X-Rays
D000817:Anilino Naphthalenesulfonates; D005456:Fluorescent Dyes; D006657:Histones; D046912:Multiprotein Complexes; D011994:Recombinant Proteins; C027132:1-anilino-8-naphthalenesulfonate