Tag-Lite, the prefered ligand binding technology

The non-radioactive Tag-lite® solution is quickly becoming the industry standard for studying receptor-ligand binding interactions.
The solution continues to demonstrate its effectiveness in the lab, taking the lead over traditional SPA and radioligand binding assays. Tag-lite’s success in the field is based on benefits it provides that are not found elsewhere:

No separation steps

Cell-based solution

No radioactive waste

Small quantities of labeled ligands

Tag-lite binding assays portfolio

18 validated receptors, and counting

Cisbio scientists have validated 18 Tag-lite binding assays as of this writing. If the receptor you wish to study is not listed, remember that Cisbio’s team of experienced experts works hand-in-hand with clients to create custom binding solutions. All ligand binding assays listed here include labeled cells and their matching fluorescent ligands.

Tag-lite assays complete list

Tag-lite at the bench: What to expect

Two basic binding protocols – saturation binding and competitive binding – are used to assess equilibrium dissociation constants for the labeled probe (Kd) and the unlabeled compounds (Ki).

Saturation binding assay

Kd determination

To determine Kd, the fluorescent ligand is titrated into a solution containing a fixed amount of labeled cells, and then incubated to equilibrium. The video below provides an overview of the protocol.

Competitive binding assay

Ki determination

To determine Ki, the compound is titrated into a solution containing a fixed concentration of fluorescent ligand and a fixed quantity of cells. At equilibrium, the fraction of labeled ligand bound to the receptor is proportional to the recorded FRET signal. Binding affinities are calculated from this resulting signal. The video below provides an overview of the protocol.

Kinetic binding and residence time

Growing evidence suggests that ligand–receptor binding kinetics is an overlooked factor in drug discovery. Cisbio has developed Tag-lite® kits and services to address the kinetic binding needs of GPCR researchers around the world.

Binding kinetics relates to the rate of association and dissociation of a drug-protein complex. Binding kinetics is thought to be a critical parameter for optimizing the in vivo efficacy of drug candidates. As such, kinetics is receiving increasing attention in drug discovery efforts. Tag-lite combines the flexibility of a radioligand binding with the advantages of homogeneous nonradioactive technologies such as SPR. The homogeneous character of Tag-lite enables binding events to be monitored continually without ever having to stop the reaction.

Motulsky and Mahan described equations that could be used for studying the kinetics of competitive binding. Fitting of data using Tag-lite to these equations allows the determination of the association and dissociation rate constants of the unlabeled competing ligand.

Using Tag-lite and a Motulsky & Mahan equations, the Kon and Koff of 2 muscarinic M1 receptor bindiners were calculated (Atropine and Pirenzepine):

Association Rate Constant: The Unsung Hero of Drug Discovery Kinetics - Webinar

On-Demand Webinar: measuring association rates

While the importance of ligand-receptor binding kinetics on drug action is becoming well established, focus to date has been almost entirely on the role of the dissociation constant. This on-demand webinar features Nicolas Pierre and the renowned pharmacologist Prof. Steven Charlton and aims to highlight the importance of association rate constant.

Watch webinar

Determination of association and dissociation rates constants

If, like Stephen Charlton, you are ready to use Tag-lite for all your kinetic needs, this application note is your next step. It describes how binding kinetics studies can be enriched with a Kon, Koff approach by providing critical data on how the association and dissociation rates of a receptor-ligand couple can be assessed with streamlined no-wash Tag-lite assays.

Read this technical note

Determination of association and dissociation rate constants using the Tag-lite platform application note

Binding assay: do it yourself

Tag-lite offers freedom and flexibility to build up your assays from target construction to assay development.

A plasmid construction is engineered with Tag-lite plasmids and the gene encoding your protein of interest. Once transfected into cells, these plasmids lead to the expression of a protein fused with the tag. The tagged protein covalently and specifically interacts with Tag-lite substrates.

Build your target with Tag-lite plasmids

Cisbio has optimized a plasmid encoding SNAP bordered by restriction sites, for cloning a gene of interest. By using this plasmid, a construction can be engineered. This construction encodes for the protein of interest and SNAP-Tag in the N or C terminal position.

Label your tagged target with Tag-lite substrates

A selection of substrates labeled with HTRF fluorophores is also proposed for SNAP-tag.


Plasmid selection

Choose an empty plasmid among the 3 different selection markers: Hygromycin, Neomycin, Zeocin.


GPCR cloning

Using standard cloning techniques, insert the GPCR gene of interest into the empty plasmid.


Cell transfection

Using standard transfection techniques, transiently express the TAG-GPCR of interest in your cell line.


Cell labeling

Use one of the appropriate TAG substrates to specifically and covalently label the TAG-GPCR with a cryptate donor

Labeling procedure


Binding assays

Perform the binding assay you designed and built!

Expert services to satisfy your exact needs

In addition to providing ready-to-use solutions, Cisbio’s team of experienced experts also works hand-in-hand with clients to create custom solutions. From compound characterization, to small- and large-scale reagent preparation and full assay development, Cisbio is the ideal trusted partner to support all your receptor binding needs.

Service Overview