Membrane Protein Affinity Measurement Service

Background Services Published Data FAQ Resources

Membrane proteins play significant role in many biological processes including ions transportation, energy transduction, signal recognition and catalysis of chemical reaction. However, due to the difficulties in obtaining high-resolution protein structures in natural status, it is challenging to detect ligand-receptor interaction of membrane proteins. Based on our classical SPR platform, Creative Biolabs can carry out the membrane protein interaction assay in a native or native-like environment and high throughput manner.

Background

Surface plasmon resonance (SPR) is one of the most powerful techniques for the study of molecular interactions. It is capable of measuring real-time binding affinity and kinetic in a label-free mode, which requires the ligand to be immobilized on a sensor chip, while allows the soluble analyte to flow across the sensor surface in the running buffer. The process is monitored by an optical element that can detect the tiny changes in refractive index near the surface. Normally, membrane proteins are difficult to be immobilized onto the sensor surface without affecting its activity. Thus, a lipid-reconstituted or detergent-solubilized conditions that can retain the membrane proteins in its active conformation are always required. Depending on the specific characteristics of each membrane protein, we provide certain different ligands to form the first layer on the chip in order to capture the membrane proteins at an appropriate orientation. With the receptor molecules attached to the first layer, ligands at a known site distinct from the interesting site help to orient the membrane protein towards the analyte flow rather than towards the sensor surface. To evaluate the specific binding interactions, positive and negative controls will be used before the formal measurement.

Figure 1. Immobilized rhodopsin for monitoring G protein activation.

Many candidates that bind to membrane proteins are small molecules (molecular weight < 1000 Da). Since the SPR effect depends on the detection of a mass change at the sensor surface, it always be a challenge thing to use a relative small-molecule as the free ligand. However, our scientists have extensive experience in balancing the ligand density for maximum activity and minimum denaturation.

Though expressing membrane protein in bilayer is preferable for affinity analysis, in some cases, to use a sample dissolved in detergent might be sufficient for an approximate measurement. To choose a cost-effective procedure, we are able to perform a Biacore-based assay to figure out the membrane proteins solubility. However, be different from cell-based assay, this test has to be evaluated case by case, as certain molecules, for example CCR5 and CXCR4, show similar KD values in the existence of detergent.

Affinity Measurement for Membrane Proteins

Creative Biolabs provides state of the art surface plasmon resonance microscopy (SPRM) that enables the measurement of binding kinetics of membrane proteins within a single living cell which keeps their original membrane environment rather than the artificial lipid bilayer or detergent solutions. Briefly, cells are directly cultured on the chip and the image is collected via an inverted microscope, which significantly enhances the sensitivity compared to traditional SPR.

Figure 2. Next-generation SPR instrumentation for measuring membrane protein-ligand binding.

Other optional Antibody Affinity Measurement Services:

Published Data

SPR Screening to Identify Active and Selective Adenosine Receptor Binding Fragments

Fig. 2 Binding responses of positive control and negative control binding to the A2A receptor and reference proteins. (Claire Shepherd, 2022)

The flux and sensitivity of surface plasmon resonance (SPR) make it an important technique for measuring low affinity and ultra-low molecular weight fragments (< 200 Da) in the early stages of drug discovery and are widely used to study ligand-protein interactions. However, the biochemical properties of membrane proteins make it particularly challenging to screen their fragments. Here, the researchers used SPR-based biosensors to study the entire family of human adenosine receptors and screened a series of novel bioactive binders with selectivity for human adenosine 2a receptors from ultra-low molecular weight fragment libraries and kinase libraries. Therefore, this proves the ability of SPR to screen ultra-low affinity fragments and identify chemical fairness with biological significance.

References

Patching S G. Surface plasmon resonance spectroscopy for characterisation of membrane protein–ligand interactions and its potential for drug discovery[J]. Biochimica et Biophysica Acta (BBA)-Biomembranes, 2014, 1838(1): 43-55.
Shepherd, Claire, et al. "Surface plasmon resonance screening to identify active and selective adenosine receptor binding fragments." ACS Medicinal Chemistry Letters 13.7 (2022): 1172-1181.

FAQ

How does temperature influence SPR measurements of membrane protein interactions?
Temperature can significantly affect SPR measurements of membrane protein interactions. It influences the fluidity of the membrane and can alter the conformation and dynamics of membrane proteins, potentially affecting binding affinity and kinetics. For accurate and reproducible results, it is crucial to maintain a consistent temperature throughout the experiment. Typically, experiments are conducted at physiological temperatures (around 37°C) to mimic biological conditions, unless specific interaction dynamics are being studied at different temperatures.
Can SPR microscopy detect low-affinity interactions of membrane proteins?
SPR microscopy is capable of detecting low-affinity interactions of membrane proteins. This sensitivity is particularly useful in drug discovery and biological research where identifying weak interactors can be crucial. The key to detecting such interactions effectively is optimizing the flow rate and concentration of the analyte, as well as ensuring that the membrane proteins are properly immobilized and oriented on the sensor chip to maintain their native conformation and functionality.
How does SPR compare to other techniques for measuring membrane protein interactions?
SPR provides real-time, label-free detection of binding events. This allows for the analysis of binding kinetics and affinity without the need for fluorescent or radioactive labels, which can potentially alter protein function. Compared to techniques like fluorescence resonance energy transfer (FRET) or co-immunoprecipitation, SPR can offer more direct and quantitative insights into the interaction dynamics. However, it requires careful preparation and handling of membrane proteins to preserve their native state on the sensor chip.