Negative SPR Signals during Low Molecular Weight Analyte Recognition.

Area of Science:

• Biophysical techniques
• Biomolecular interaction analysis
• Surface plasmon resonance (SPR)

Background:

• SPR is a label-free, real-time technique for studying biomolecular interactions.
• SPR signals are typically positive, but negative signals have been rarely observed.
• The cause of negative SPR signals remains largely unexplained.

Purpose of the Study:

• To investigate and elucidate the phenomenon of negative SPR signals.
• To test the hypothesis that negative SPR signals reflect major ligand conformational changes upon target binding.
• To understand the factors influencing complex refractive index increment (RII) deviations.

Main Methods:

• Utilized surface plasmon resonance (SPR) spectroscopy.
• Analyzed sensorgrams exhibiting negative signals.
• Investigated the refractive index increment (RII) of ligand-analyte complexes.
• Examined the influence of biomolecular conformation and immobilization on SPR signals.

Main Results:

• Negative SPR signals are caused by a negative deviation in the complex RII from the sum of individual RIIs.
• This deviation counterbalances the signal increase from target recognition and ligand folding.
• Biomolecular conformation changes can lead to positive or negative complex RII deviations, dependent on sequence and immobilization.

Conclusions:

• Negative SPR signals provide insights into significant ligand conformational changes during binding.
• The refractive index increment (RII) of the complex is a critical factor in SPR signal interpretation.
• SPR signal polarity is influenced by biomolecular sequence, conformation, and immobilization strategy.