Streptavidin-XLent HTRF®

XL665-labeled Streptavidin for capturing biotinylated proteins, peptides, antibodies, small molecules, nucleic acids....
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  • No-wash No-wash
  • Ease-of-use Ease-of-use
  • High affinity High affinity
XL665-labeled Streptavidin for capturing biotinylated proteins, peptides, antibodies, small molecules, nucleic acids....


Streptavidin has been labeled with XL665. The streptadivin-XLent! (SA-XLent!) results from a special in-house conjugation process leading to a high grade conjugate with enhanced fluorescent properties. Biotin binds to Streptavidin with high affinity (Ka=1015M-1). The binding is rapid and stable, making it an ideal choice for use in a variety of assays such as enzyme assays, protein-protein binding assays and molecular biology assays.



Assay principle

In an HTRF interaction assay, one partner is labeled (directly or indirectly) with the donor, and the other with the acceptor (again, directly or indirectly). The intensity of the signal is proportional to the binding of the 2 partners. In the example shown here: Streptavidin-XLent! binds to the biotinylated partner A while partner B* binds to a specific antibody labeled to an HTRF donor. *partner B can also be tagged, Fc fused. In these cases use for the detection, the corresponding HTRF reagent (anti-Tag, anti-species, protA, Streptavidin), labeled with donor.
assay principle of detection assay using HTRF Streptavidin-XLent!

Assay protocol

The example on the right describes the protocol using a 20 µL final assay volume for detecting an interaction between a biotinylated-tagged partner A and a non-tagged partner B*. Dispense the 2 partners (10 µL), incubate, add Streptavidin-XLent! (5 µL) and anti-partner B labeled with acceptor (5 µL), incubate and read. *partner B can also be tagged, Fc fused or directly labeled. In these cases use for the detection, the corresponding HTRF reagent (anti-Tag, anti species, protA, Streptavidin), labeled with donor.
assay protocol of detection assay using HTRF Streptavidin-XLent!

Build HTRF interaction assays for your specific application

Reagents are sold by the number of tests (20 µL reactions). XL665 or d2 conjugatesare supplied on the basis of 20 ng of antibody per well. The amount of active moiety per vial is also provided (as well as the number of tracers per vial - see product description sheet). The active moiety is defined as the active part of a conjugate (e.g. antibody).

How do the number of tests relate to active moiety?

The average conjugate quantity per well reflects overall biological material content. Using the active moiety amount is generally preferred to the quantity of total conjugate. For Cryptate and d2 conjugates, the total conjugate amount equals that of the active moiety, since the molecular weight of the label is negligible. This is not the case for XL665 labeled entities for which the quantity of total conjugate will vary depending on the final molar ratio of the XL665 conjugate, however, the amount of active moiety, provided by Cisbio, is constant and based on the number of tests ordered.
description of the active moiety in an HTRF conjugate
Description Active Moiety/5,000 tests
Streptavidin XLent! 250 µg

Recommended quantities of Cryptate and XL665 conjugates

Cryptate conjugates must not be excessive in order to prevent reader saturation and an unacceptable level of background. In most cases, a cryptate concentration of 1 to 5nM is appropriate, and will generate 20,000 to 80,000 cps at 620 nm depending on the HTRF compatible reader used. The XL665 conjugate must match its assay counterpart as closely as possible in order for the maximum number of biomolecules to be tagged with the XL665 acceptor. Thus, to detect a tagged molecule at an assay concentration of 20nM, the concentration of anti-Tag-XL665 should be equimolar or higher.

HTRF Tyrosine kinase assay

HTRF reagents (Europium-Cryptate PT66 and Streptavidin-XLent!) and conjugates from two other suppliers were used in an HTRF tyrosine kinase assay. When compared to competitor, Streptavidin-XLent! shows overall superior performance
results of a tyrosine kinase assay using HTRF Streptavidin-XLent! for detection

SaXLent! compared to SaXL on the EGFR tyrosine kinase assay

Increasing quantities of EGFR were incubated with biotinylated polyGAT (50 nM). The enzymatic reaction was stopped using EDTA following a 20 minute incubation. Europium-labeled PT66 (20 ng/well) and Streptavidin-XL665 (50 nM) or StreptavidinXLent! (50 nM) were added. HTRF signal was detected following a 20 minute incubation. In addition to the increased sensitivity, over 25% less enzyme was required when using streptavidin-XLent! to produce identical assay signals.
HTRF SaXL compared to HTRF SAXLent! on an EGFR assay

Exploiting HTRF for novel drug classes: Stabilizing 14-3-3 protein-protein interactions

In collaboration with Lead Discovery Center GmbH - Scientific Presentations

Experience the freedom of building your own assay

HTRF kinase activity toolbox reagents - Flyers

HTRF protein-protein interaction reagents

Benefit from unlimited flexibility for your assay development - Flyers

Addressing the interactome with protein-protein assays

Cover all PPIs with one approach - Brochures

HTRF -A Beneficial Tool for Lead Optimization of Biotherapeutics

In collaboration with Boehringer Ingelheim - Posters

HTRF PPI your dream assay served on a plate

Sandwiches aren't just for eating - Infographics

Best practices for pharmacological characterization of PPI inhibitors

Easy pharmacological characterization of PPI modulators. - Technical Notes

HTRF assays handle low- to high affinity protein-protein interactions

Deciphering low- and high affinity interactions - Application Notes

Nuclear receptor ligand identification with HTRF

Monitoring nuclear receptor binding with HTRF assays - Application Notes

HTRF addresses large protein-protein interaction complexes

Challenge large complexes with HTRF assays - Application Notes

A brief history of Protein-Protein Interactions

How well do you know PPI? - Infographics

HTRF Product Catalog

All your HTRF assays in one document! - Catalog

A guide to Homogeneous Time Resolved Fluorescence

General principles of HTRF - Guides

How HTRF compares to Western Blot and ELISA

Get the brochure about technology comparison. - Brochures

Virology research solutions using HTRF Protein-Protein Interaction assays

See how peer researchers challenge the viral life cycle with PPI assays - Application Notes

Solutions for CAR-T research

Advance your CAR-T cell research - Flyers

Batch Information Streptavidin-ent-XL / 20230423

611SAXLA Batch 25C - Batch Information

Batch Information Streptavidin-ent-XL / 20230503

611SAXLA Batch 26A - Batch Information

Batch Information Streptavidin-ent-XL / 20230108

611SAXLB Batch 25B - Batch Information

Batch Information Streptavidin-ent-XL / 20230503

611SAXLB Batch 26A - Batch Information

Plate Reader Requirement

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