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Single-Molecule Imaging of Nuclear Transport
Published on: June 9, 2010
Biophysical characterization of interactions involving importin-alpha during nuclear import
1Ludwig Institute for Cancer Research, Royal Melbourne Hospital, Victoria 3050, Australia.
The Journal of Biological Chemistry
|July 13, 2001
Summary
Nuclear import proteins bind importin-alpha, which is regulated by an autoinhibitory domain. Importin-beta binding enhances NLS binding, facilitating nuclear transport regulation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Nuclear localization sequences (NLSs) mediate protein import into the nucleus.
- The importin-alpha/beta heterodimer facilitates this process, with importin-alpha binding NLSs and importin-beta mediating pore translocation.
Purpose of the Study:
- To characterize the interactions of importin-alpha during nuclear import.
- To elucidate the regulatory mechanism of importin-alpha's NLS binding.
- To quantitatively describe the binding and regulatory steps in nuclear import.
Main Methods:
- Biosensor assays
- Crystallography
- Sedimentation equilibrium
- Electrophoresis
- Circular dichroism
Main Results:
- Importin-alpha exists in an autoinhibited monomeric state, with NLS association undetectable by biosensor.
- Importin-beta binding (1:1 stoichiometry, K(D) = 1.1 x 10(-8) M) significantly increases importin-alpha's affinity for NLSs.
- The importin-alpha/beta complex binds monopartite and bipartite NLSs with affinities (K(D) ~3.5-4.8 x 10(-8) M) comparable to truncated importin-alpha.
- The autoinhibitory domain binds importin-alpha, and its complex structure mimics full-length importin-alpha.
Conclusions:
- Results support a model of nuclear import regulation via importin-alpha's intrasteric autoregulatory sequence.
- A quantitative description of binding and regulatory steps in nuclear import is provided.
- The study elucidates the mechanism of importin-alpha's role in nuclear transport regulation.
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