ANS Interacts with the Ca²⁺-ATPase Nucleotide Binding Site

Area of Science:

• Biochemistry
• Molecular Biology
• Biophysics

Background:

• The sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) is crucial for muscle contraction.
• Understanding its nucleotide binding domain (N-domain) is key to SERCA function.
• 8-anilino-1-naphthalene sulfonate (ANS) is a fluorescent probe often used to study protein interactions.

Purpose of the Study:

• To investigate the binding of ANS to the N-domain of SERCA.
• To characterize the binding modes and affinity of ANS.
• To explore the potential of ANS as a fluorescent probe and inhibitor for SERCA.

Main Methods:

• Molecular docking simulations to predict binding modes.
• Fluorescence spectroscopy to confirm ANS binding and interaction.
• Molecular dynamics simulations to assess binding stability.
• Förster Resonance Energy Transfer (FRET) analysis.
• Chemical modification (NBS) to probe structural changes.
• Enzyme kinetics assays (Dixon plot) to determine inhibition type.

Main Results:

• Molecular docking identified two potential binding modes (BMI and BMII) for ANS.
• ANS fluorescence intensity increased upon binding to the N-domain, confirming interaction.
• Molecular dynamics simulations indicated BMI, occupying the ATP site, is the stable mode.
• ANS binding hindered FITC labeling, suggesting occupation of the ATP binding site.
• ANS showed a higher affinity for the N-domain than ATP.
• FRET analysis suggested a Trp-ANS interaction, but NBS modification indicated structural rearrangements instead of FRET.
• ANS exhibited partial mixed-type inhibition of Ca²⁺-ATPase activity.
• Dixon plot analysis supported the existence of a catalytically active dimeric Ca²⁺-ATPase.

Conclusions:

• ANS binds to the ATP binding site of the SERCA N-domain with high affinity.
• ANS binding induces structural rearrangements within the nucleotide binding site.
• ANS serves as a valuable fluorescent probe for studying SERCA's nucleotide binding site.
• ANS shows potential as a molecular platform for developing novel Ca²⁺-ATPase inhibitors.