The QIAexpress Assay System is designed for improved assays using 6xHis-tagged biomolecules in a wide range of applications.
| QIAexpress Assay Product Options | ||
| Amount of
protein captured per well |
Format | QIAexpress assay product |
| 3每15 µg (125每625 pmol of a 24 kDa protein) |
Magnetic-bead suspension | Ni-NTA Magnetic Agarose Beads |
| 0.3 µg (12.5 pmol of a 24 kDa protein) |
Multiwell strips and plates | Ni-NTA HisSorb Strips and Plates |
The QIAexpress Assay System uses the strong 6xHis每Ni-NTA interaction to immobilize functionally active proteins and other biomolecules for improved assays. 6xHis-tagged biomolecules can be selectively captured from complex mixtures of molecules, such as cell lysates. The biomolecules are bound in a uniform orientation offering optimal presentation of binding domains to interacting partners, resulting in higher signal-to-noise ratios and reliable, reproducible results. Proteins that are expressed from the pQE-100 DoubleTag vector have an N-terminal 6xHis tag and a C-terminal Tag﹞100. These doubly tagged proteins are conveniently immobilized on Ni-NTA HisSorb Strips and Plates or Ni-NTA Magnetic Agerose Beads via the 6xHis tag and detected using the Tag﹞100 Antibody. This eliminates the need for antibodies specific for each individual protein of interest and enables a wide range of assays.
The QIAexpress Assay System allows a wide range of capture assays to be performed including protein每protein interaction, protein每DNA interaction, and ELISA procedures. In a typical assay procedure, 6xHis-tagged molecules are selectively bound to Ni-NTA. After washing (if necessary) interaction partners are bound. After further washing, the interacting partners are detected. The high-affinity interaction between Ni-NTA and the 6xHis tag is unaffected by a variety of reagents, such as strong denaturants and many detergents, which allows stringent washing and elimination of nonspecific interactions (see table "Reagents compatible with the Ni-NTA每6xHis interaction").
A choice of assay products is available for the immobilization any amount of 6xHis-tagged protein. The application determines the appropriate assay system. For applications involving low-affinity interactions, Ni-NTA Magnetic Agarose Beads are recommended. Their high binding capacity and ability to present bound assay components to interaction partners with high steric accessibility, results in sensitive detection even with weakly interacting assay components. Ni-NTA Magnetic Agarose Beads can be used in microcentrifuge tubes or 96-well microplates, and the amount of beads used can easily be adjusted to meet specific assay requirements.
In general, Ni-NTA HisSorb Strips or Plates are more suitable for assays using biomolecules which interact with high-affinity and when small amounts of 6xHis-tagged protein are sufficient to produce strong signals in a single well. Assays using Ni-NTA HisSorb Strips or Plates can be conveniently performed using standard ELISA techniques and equipment.