Protein Interaction Analysis

Protein interactions are intrinsic to virtually every biological process in cells. Protein interaction analysis provides insight into biology for example, DNA replication, transcription, translation, signal transduction, transport across membranes, cell cycle control, cell metabolism, and muscle contraction. In consequence, protein-protein interactions (PPIs) have been studied extensively in the area of bioscience and medical research.

Protein Interaction Analysis Service

Biologics International Corp. (BIC) has organized a team of scientists with expert knowledge and extensive experience in the field of protein interaction. Our dedicated teams strive to assist you with experiment design, carry out your experiments, and perform data analysis. The comprehensive protein interaction analysis service offered by BIC includes glutathione S-transferase (GST) pull-down, co-immunoprecipitation (co-IP) and bio-layer interferometry (BLI).

GST Pull-down



We can measure wide range of biomolecular interactions including protein to protein, DNA to protein, metabolite to protein, antibody to antigen, enzyme to substrate/inhibitor, and small molecule to drug target interactions. If you are not sure which approach to choose, please contact us for a recommendation.

Methods of Protein Interaction Analysis

GST Pull-down

Pull-down assay techniques are in vitro methods for determining the physical interaction between two or more proteins. The principle of pull-down assay is using tags (such as GST, poly-His and biotin) to trap the target protein, which is essentially an affinity purification.

GST pull-down is a pull-down assay technique that can be used to confirm existing protein-protein interactions discovered by other techniques or as an initial screening to identify novel protein-protein interactions. By subsequent elution and analysis using western blot or mass spectrometry, a predicted interaction can be confirmed or previously unknown interactions can be discovered. The pull-down technique has become an invaluable tool for the life scientist interested in studying cellular pathways via protein-protein interactions.
For more information on this service, please refer to our GST pull-down page.


Immunoprecipitation (IP) is a technique used to isolate a specific protein or nucleic acids out from a solution, and is similar to pull-down assay, except that this method uses an antibody, instead of a bait protein to trap the target protein or nucleic acids. Co-IP is a more delicate version of a traditional IP.

Using target protein-specific antibodies to indirectly trap proteins that are bound to a specific target protein, co-IP can separate the target protein from a sample (such as serum and cell lysate) containing thousands of different proteins. During co-IP assay, proteins interact under non-denaturing conditions, which approximate physiological conditions. After the assay, immobilized immune complexes can be collected, eluted from the support, and identified, thereby revealing the composition of the retrieved multimers. Learn more about our co-IP service.


BLI measures biomolecular interactions by analyzing interference patterns of white light reflected from the surface of a biosensor tip. Like surface plasmon resonance (SPR), BLI is also a well-established optical label-free technique to detect and monitor biomolecular interactions in real time.

SPR relies on the refractive indices of the solution and analyte. If the difference in refractive indices is insufficient or samples contain high levels of glycerol, SPR can’t work. BLI measures only what is bound to the biosensor, which allows us to work directly with crude and unpurified samples.

In BLI experiment, one molecule (such as a protein) is immobilized to a biosensor and binding to a second molecule is measured. The interaction occurs at the very tip of a glass fiber-based BLI biosensor. White light passing through the glass fiber is reflected back from both the internal surface and the external interface (with the sample solution). As more molecules bind to the sensor, the variation in thickness of the external layer of immobilized protein causes shifts in the interference pattern. The pattern can be plotted as a nanometer shift of relative intensity vs. wavelength that can be recorded in real time with high precision and accuracy. Consult our bio-layer interferometry page for more details.

Comparison of Different Methods of Analyzing Protein Interactions

In addition to the above three methods, protein interactions usually require a combination of techniques to validate, characterize, and confirm them. Below are some other contemporary approaches utilized for detection and analysis of protein-protein interactions, each one with its own advantages and weaknesses.

Techniques Principle
Yeast two-hybrid (Y2H) Monitors complex formation through transcriptional activation of reporter genes.
Far-western blotting Similar strategy to western blotting with one key difference. The antibody probe in a typical western blotting detection is substituted with an labeled bait protein as the probe.
Tandem affinity purification-mass
TAP-MS is based on the double tagging of the protein of interest on its chromosomal locus, followed by a two-step purification process and mass spectroscopic analysis.
Protein array A high-throughput method, it is used to track the interactions and activities of proteins and to determine function on a large scale.
Phage display technology Obtain optimal protein binding by immobilization of an antigen on magnetic beads and screening against a phage display library.

Need more information? Please do not hesitate to get in touch.

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