Calorimetric studies of the interactions of linker histone H1~0 and its carboxyl (Hl°-C) and globular (Hl°-G) domains with calf-thymus DNA

摘要

Histone HI is a chromatin protein found in most eukaryotes. ITC and CD have been used to study the binding of H1~0 and its C-terminal, Hl~0-C, and globular, Hl~°-G, domains to a highly polymerized DNA. ITC results indicate that H1~0 and Hl~°-C bind tightly to DNA (K_a= 1 x 10~7), with an unfavorable DELTAH (DELTAH = +22 kcal/mol) and a favorable AS (-TAS = -30 kcal/mol). Binding Hl~0-G to DNA at 25 °C is calorimetrically silent. A multiple independent site model fits the ITC data, with the anomaly in the data near saturation attributed to rearrangement of bound HI, maximizing the number of binding sites. CD experiments indicate that H1°/DNA and H1~°-C/DNA complexes form with little change in protein structure but with some DNA restructuring. Salt dependent ITC experiments indicate that the electrostatic contribution to binding H1~0 or Hl~°-C is small ranging from 6% to 17% of the total AG.