Do conformational changes contribute to the surface plasmon resonance signal?

Area of Science:

• Biophysical Chemistry
• Molecular Biology
• Analytical Chemistry

Background:

• Surface plasmon resonance (SPR) biosensors are crucial for studying molecular interactions.
• The contribution of molecular conformational changes to SPR signals remains debated.
• Previous studies often lacked rigorous controls or comprehensive analysis of contributing factors.

Purpose of the Study:

• To investigate whether molecular conformational changes affect SPR signals.
• To quantify the contribution of conformational changes using a well-characterized DNA aptamer.
• To resolve the debate on SPR signal interpretation.

Main Methods:

• Utilized a thrombin-binding DNA aptamer (TBA) that forms a G-quadruplex structure upon potassium ion binding.
• Experimentally determined all factors contributing to the SPR response, including refractive index increment (RII) and fraction of immobilized TBA.
• Compared theoretical SPR responses with experimental SPR responses using appropriate controls.

Main Results:

• Theoretical SPR responses consistently underestimated experimental SPR responses.
• Discrepancies were observed regardless of the method used to measure RII or the amount of available TBA.
• The study provides strong evidence for the influence of conformational changes on SPR signals.

Conclusions:

• Conformational changes in molecules demonstrably contribute to the measured SPR signal.
• This finding has significant implications for the interpretation of SPR data in various scientific fields.
• The study establishes a robust experimental model for investigating SPR signal contributions.