We have studied the secondary structure of the carboxyl-terminal domains of linker histone H1 subtypes H1° (C-H1°) and Hit (C-H1t), free in solution and bound to DNA, by IR spectroscopy. The carboxyl-terminal domain has little structure in aqueous solution but becomes extensively folded upon interaction with DNA. The secondary structure elements present in the bound carboxyl-terminal domain include the α-helix, β-structure, turns, and open loops. The structure of the bound domain shows a significant dependence on salt concentration. In low salt (10 mM NaCl), there is a residual amount of random coil, 7% in C-H1° and 12% in C-H1°. In physiological salt concentrations (140 mM NaCl), the carboxyl termini become fully structured. Under these conditions, C-H1° contained 24% α;-helix, 25% β-structure, 17% open loops, and 33% turns. The latter component could include a substantial proportion of the 310 helix. Despite their low sequence identity (̃30%), the representation of the different structural motifs in C-H1t was similar to that in C-H1°. Examination of the changes in the amide I components in the 20-80 °C temperature interval showed that the secondary structure of the DNA-bound C-H1t is for the most part extremely stable. The H1 carboxyl-terminal domain appears to belong to the so-called disordered proteins, undergoing coupled binding and folding. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.
|Journal||Journal of Biological Chemistry|
|Publication status||Published - 16 Sep 2005|