Calorimetric studies of the interactions of linker histone H10 and its carboxyl (H10-C) and globular (H10-G) domains with calf-thymus DNA

Histone H1 is a chromatin protein found in most eukaryotes. ITC and CD have been used to study the binding of H10 and its C-terminal, H10-C, and globular, H10-G, domains to a highly polymerized DNA. ITC results indicate that H10 and H10-C bind tightly to DNA (Ka ≈ 1 × 107), with an unfavorable ΔH (ΔH ≈ + 22 kcal/mol) and a favorable ΔS (− TΔS ≈ − 30 kcal/mol). Binding H10-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 H1, maximizing the number of binding sites. CD experiments indicate that H10/DNA and H10-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 H10 or H10-C is small ranging from 6% to 17% of the total ΔG.