Thermodynamic Analysis of H1 Nuclear Import

The nuclear import of H1 linker histones is mediated by a heterodimer of transport receptors, known as importinβ and importin7. Interestingly, both importins separately interact with H1, but only as a dimer they facilitate the translocation through the nuclear pore. We identified the H1 binding site...

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Bibliographic Details
Published in:The Journal of biological chemistry 2007-04, Vol.282 (14), p.10707-10719
Main Authors: Wohlwend, Daniel, Strasser, Anja, Dickmanns, Achim, Doenecke, Detlef, Ficner, Ralf
Format: Article
Language:English
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Summary:The nuclear import of H1 linker histones is mediated by a heterodimer of transport receptors, known as importinβ and importin7. Interestingly, both importins separately interact with H1, but only as a dimer they facilitate the translocation through the nuclear pore. We identified the H1 binding site of importin7, comprising two extended acidic loops near the C terminus of importin7. The analysis of the H1 import complex assembly by means of isothermal titration calorimetry revealed that the formation of a receptor heterodimer in vitro is an enthalpy-driven process, whereas subsequent binding of H1 to the heterodimer is entropy-driven. Furthermore, we show that the importinβ binding domain of importin7 plays a key role in the activation of importin7 by importinβ. This process is allosterically regulated by importinβ and accounts for a specific tuning of the activity of the importinβ·importin7 heterodimer. The results presented here provide new insights into cellular strategies to even energy balances in nuclear import and point toward a general regulation of importinβ-related nuclear import processes.
ISSN:0021-9258
1083-351X
DOI:10.1074/jbc.M610409200