New Immobilization Method Developed to Improve Membrane Protein Analysis Using SPR

A team led by Wang Junfeng from the Hefei Institutes of Physical Science, Chinese Academy of Sciences, has developed a novel approach to immobilize membrane proteins for surface plasmon resonance (SPR) assays, addressing key technical limitations in this area. Their study, recently published in Analytical Chemistry, presents a method integrating the SpyCatcher-SpyTag covalent conjugation system with membrane scaffold protein (MSP)-based nanodisc technology.

Membrane proteins comprise approximately one-third of human proteins and nearly 60% of drug targets, playing essential roles in signaling and transport. Accurate analysis of their interactions is critical for both understanding biological function and drug development. SPR is a widely used, label-free technique that enables real-time measurement of biomolecular interactions including binding kinetics. However, applying SPR to membrane proteins has been challenging because it is difficult to stably immobilize these proteins while preserving their native structure and activity. 

The novel strategy uses an MSP-SpyTag fusion protein to incorporate target membrane proteins into lipid nanodiscs, which maintain a near-native lipid environment. These SpyTag-labeled nanodiscs are then captured efficiently and specifically by SpyCatcher proteins pre-immobilized on CM5 sensor chips, using standard amine coupling chemistry. This results in robust and stable immobilization of membrane proteins to the SPR sensor surface.

Using this method, the researchers analyzed three representative membrane protein interactions: protein–lipid, transmembrane protein–antibody, and transmembrane protein–small molecule. The approach consistently generated high-quality kinetic data, enabling precise quantification of binding affinities and rates. The method also demonstrated improved stability compared to traditional immobilization techniques, reducing protein aggregation and desorption during assays.

This immobilization approach overcomes major obstacles in studying membrane proteins with SPR, preserving protein integrity in a biologically relevant environment. It holds significant promise for advancing membrane protein research and facilitating drug discovery by enabling more reliable real-time interaction analysis.