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  • SNAP-Capture Magnetic Beads


    The SNAP-Capture Magnetic Beads are used to selectively immobilize and magnetically separate a SNAP-tag® fusion protein from solution using magnetic agarose beads. These beads show a low non-specific absorption of proteins from a complex lysate, making them suitable for pull down applications. The SNAP-Capture Magnetic Beads are prepared by the coupling of SNAP-tag substrate benzylguanine with highly stable 75-150 µm superparamagnetic particles. Two ml of SNAP-Capture Magnetic Beads is sufficient to perform 25 immobilization assays using 80 µl of bead suspension per assay.

    The SNAP-tag is a novel tool for protein research, allowing the specific, covalent attachment of virtually any molecule or modified surface to a protein of interest. The SNAP-tag is a protein based on mammalian O6-alkylguanine-DNA alkyltransferase (AGT).  SNAP-tag substrates are derivatives of benzyl purines and benzyl pyrimidines.  In the immobilization reaction, the SNAP-tag is covalently attached to the substituted benzyl group of the SNAP-Capture Magnetic Beads.

    There are two steps to using this system: sub-cloning and expression of the protein of interest as a SNAP-tag fusion, and capture and immobilization of the fusion protein using SNAP-Capture Magnetic Beads.

    Figure 1. Substrate structure on SNAP-Capture Magnetic Beads.

    Properties and Usage

    Materials Required but not Supplied

    • Protein sample containing the protein to immobilize expressed as a SNAP-tag fusion 
    • Magnetic particle separator 
    • Buffer for immobilization and washing

    Binding Capacity

    SNAP-Capture Magnetic Beads (80 µl) were washed, incubated with 200 µl of 1 mg/ml SNAP-tag CBD (Chitin Binding Domain) for 1 hour at room-temperature, then rewashed as described in these instructions. Binding capacity was determined to be 3 mg/ml bead suspension.

    Quality Control

    Quality Control Assays

    The following Quality Control Tests are performed on each new lot and meet the specifications designated for the product. Individual lot data can be found on the Product Summary Sheet/Datacard or Manual which can be found in the Supporting Documents section of this page.
    • Binding Capacity (Affinity Tagged Bead/Resin):
      The product is tested by incubation with the appropriate affinity tagged protein and the binding capacity determined


    1. Storage of Magnetic Beads: Do not freeze the SNAP-Capture Magnetic Beads. Store the unused beads at 4°C. With proper storage, beads should be stable for at least two years.
    2. Correct storage and handling of SNAP-tag fusion proteins is essential to maintain reactivity of the SNAP-tag prior to immobilization.
    3. SNAP-tag fusion proteins can be purified before immobilization, but the immobilization reaction also works in non-purified protein solutions including cell lysates. 
    4. Add 1 mM DTT to buffers used for the storage of SNAP-tag fusion proteins. Protein samples should be stored at -20°C, or at -80°C for long-term storage. Handling at temperatures above 0°C should be minimized by thawing the SNAP-tag protein samples shortly before use, and keeping them on ice until just before the immobilization.
    5. If a particular fusion protein requires buffers without reducing agents, minimize handling steps of the protein above 4°C before the labeling reaction.
    6. The SNAP-tag itself is tolerant of a wide range of buffers. The requirements of your fusion partner should dictate the selection of the buffer. The following storage buffer composition is recommended, especially when freezing protein material: pH between 7.0 and 8.0, monovalent salts (e.g. sodium chloride) between 50 mM and 250 mM, and at least 1 mM DTT. Non-ionic detergents can be added if required, but ionic detergents should be avoided because they reduce the activity of the SNAP-tag. Many proteins benefit from the addition of glycerol for frozen storage, typically 20% v/v.
    7. Immobilized SNAP-tag fusion proteins should be stored at 4°C. Sodium azide may be added to 2 mM final concentration to prevent bacterial growth. Depending on the stability of the fusion partner, under these conditions the immobilized protein should be stable at 2–6°C for several months. The SNAP-Capture Magnetic Beads should not be frozen.
    8. The SNAP-tag fusion protein is linked to the SNAP-Capture Magnetic Beads by a covalent bond. Therefore the immobilized protein is essentially irreversibly bound to the beads. It is important however to preserve the functional stability of the protein fused to the SNAP-tag as much as possible. We recommend handling the immobilized fusion protein and storing between use at 4°C, to prepare it just before use, and to handle it as gently as possible.

    Supporting Documents

    Material Safety Datasheets

    The following is a list of Material Safety Data Sheets (MSDS) that apply to this product to help you use it safely. The following file naming structure is used to name these document files: [Product Name] MSDS. For international versions please contact us at info@neb.com.


    The Product Summary Sheet, or Data Card, includes details for how to use the product, as well as details of its formulation and quality controls. The following file naming structure is used to name the majority of these document files: [Catalog Number]Datasheet-Lot[Lot Number]. For those product lots not listed below, please contact NEB at info@neb.com or fill out the Technical Support Form for appropriate document.
    1. Cellular Imaging and Analysis FAQs
    1. Use SNAP-Capture Magnetic Beads (S9145)

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