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HTRF XIAP BIR3 Binding Kit Red Ligand, 1 Vial

HTRF XIAP BIR3 Red Ligand can be used for affinity binding experiments in association with the HTRF XIAP BIR3 Binding kit to investigate cooperativity effects within PROTAC drug discovery.

For research use only. Not for use in diagnostic procedures. All products to be used in accordance with applicable laws and regulations including without limitation, consumption & disposal requirements under European REACH regulations (EC 1907/2006).

Part number: 64XIAPFLRED
List price: USD 410.16
Your price:
USD 410.16
USD 410.16 /each


The HTRF XIAP BIR3 Red Ligand is based on labeled A410099.1 derivative and is primarily intended to perform cooperativity binding studies. It enables calculation of the affinity of the XIAP BIR3 Red Ligand for XIAP BIR3 protein in the presence of the targeted protein of interest. The Kd of HTRF XIAP BIR3 Red Ligand for XIAP protein, in absence and presence of the targeted protein, enables an accurate analysis of the cooperative effect assessed with the HTRF XIAP BIR3 binding kit.


Protein Detection
Assay Points
Assay Target Type
Fluorescent reagent
Assay Technology
Automation Compatible
Detection Method
Experimental Type
In vitro
Therapeutic Area
Oncology & Inflammation
Unit Size
1 Unit

Video gallery

How it works

HTRF XIAP ligand binding assay principle on the XIAP BIR3 binding domain

HTRF XIAP BIR3 Red Ligand binding is detected in a direct binding assay format, using an anti GST-Terbium Cryptate antibody which binds to GST-tagged Human XIAP BIR3 domain. When the dyes are in close proximity, the excitation of the donor with a light source (laser or flash lamp) triggers a Fluorescence Resonance Energy Transfer (FRET) towards the acceptor, which in turn fluoresces at a specific wavelength (665 nm) (Image A). The specific binding signal is calculated by subtracting the non-specific binding signal from the total signal, enabling Kd determination for the HTRF XIAP BIR3 Red Ligand (Image B).

HTRF XIAP BIR3 Red Ligand binding assay protocol

Saturation binding experiments of HTRF XIAP BIR3-Red Ligand can be run in 384-well plates by dispensing 5 µL of Diluent 9 buffer (for Total binding) or XIAP BIR3 Binding standard (for non specific binding). Then 5 µL of PROTAC Binding Buffer 2 (for reference) or the targeted protein diluted in PROTAC Binding Buffer 2 (for cooperativity studies) are added, followed by 5 µL of GST-tagged XIAP BIR3 protein. Finally, 5 µL of a pre-mixed solution of HTRF XIAP BIR3-Red Ligand and Anti-GST Tb cryptate antibody are added.

The HTRF Ratio is measured after 2 hours of incubation at room temperature



Assay details

HTRF XIAP BIR3-Red Ligand Kd (reference without PROTAC protein substrate) 5 nM +/- 8nM


Assay validation

Determination of the affinity binding (Kd) of XIAP BIR3-Red Ligand in the presence of targeted protein

In this example, the affinity binding (Kd) of the XIAP BIR3 Red Ligand to GST-XIAP BIR3 protein was assessed in the absence or presence of the targeted protein BRD4 (10nM or 100nM)  . This result indicates that the presence of BRD4 does not change the Kd of the Red Ligand.

Consequently this example shows that a cooperativity experiment with a PROTAC molecule composed of a XIAP ligand and a BRD4 warhead can be set up. Finally, the alpha factor can be established by dividing the Ki of the PROTAC in the binary complex (XIAPBIR3 -PROTAC) by the Ki of the PROTAC in the ternary complex (XIAPBIR3 -PROTAC-BRD4).




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