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Evidence for an F-actin like conformation in the actin:DNase I complex
B D Hambly1, P Kiessling, C G dos Remedios
1Department of Anatomy, University of Sydney NSW, Australia.
Advances in Experimental Medicine and Biology
|January 1, 1994
Summary
A modified ATP analogue, TNP-ATP, binds to polymerized actin (F-actin) and actin:DNase I complexes but not to monomeric actin (G-actin). This suggests F-actin's nucleotide binding site conformation is maintained upon DNase I binding and polymerization.
Area of Science:
- Biochemistry
- Molecular Biology
- Actin Dynamics
Background:
- Actin is a crucial protein for muscle contraction and cell motility.
- Understanding nucleotide binding site dynamics in actin is key to elucidating its functions.
- The conformational states of actin monomers (G-actin) and polymers (F-actin) differ, impacting their interactions.
Purpose of the Study:
- To investigate the nucleotide binding properties of actin using a modified ATP analogue, TNP-ATP.
- To compare the nucleotide binding site conformation in G-actin, F-actin, and the actin:DNase I complex.
- To explore the functional implications of these conformations on actin's interaction with myosin and calcium regulation.
Main Methods:
- Utilized TNP-ATP, a ribose-modified analogue of ATP, to probe nucleotide binding.
- Studied nucleotide exchange in G-actin, F-actin, and actin:DNase I complexes.
- Assessed F-actin's functional properties, including superprecipitation with myosin and Ca(2+)-sensitivity.
Main Results:
- TNP-ATP exchanges with nucleotides in F-actin but does not bind to G-actin.
- TNP-ATP binds to actin within the actin:DNase I complex, indicating a conformation similar to F-actin.
- Ca(2+)-sensitive regulation of F-actin is not affected by nucleotide binding site conformation changes.
Conclusions:
- Actin polymerization or DNase I binding limits the domain flexibility observed in G-actin.
- The nucleotide binding site conformation in F-actin is functionally similar to native ADP-F-actin.
- Calcium-sensitive thin filament regulation does not involve significant conformational changes near the nucleotide binding site.