Recombinant Human FKBP5 Protein: Handling & Application Protocol

Recombinant Human FKBP5 Protein is a eukaryotically expressed, immunophilin co-chaperone used to study glucocorticoid receptor regulation, stress-response pathways, and FK506-binding activity in biochemical and cell-based assays.

Product Name

Recombinant Human FKBP5 Protein

SKU

rp367720

Protein Aliases

FKBP51, FKBP54, AIG6, p54, Hsp90-binding immunophilin

Biological Function

Co-chaperone of Hsp90; negative regulator of glucocorticoid receptor nuclear translocation; involved in stress-response and PTSD-linked signaling

Recommended Storage

Avoid repeated freeze-thaw cycles; store aliquots at -80 °C for long-term use

Typical Applications

Biochemical binding assays, ELISA, Western blot validation, co-immunoprecipitation, and glucocorticoid receptor interaction studies

Background: FKBP5 Biology and Research Relevance

FKBP5 (FK506-binding protein 5, also known as FKBP51) is a member of the immunophilin family of peptidyl-prolyl isomerases. It functions as an Hsp90-associated co-chaperone and plays a central role in modulating glucocorticoid receptor (GR) sensitivity by retaining the GR–Hsp90 complex in the cytoplasm, thereby attenuating nuclear translocation and transcriptional activity.

Elevated FKBP5 expression is associated with stress-axis dysregulation, post-traumatic stress disorder (PTSD), depression, and glucocorticoid resistance in immune and endocrine contexts. FKBP5 is also implicated in NF-κB signaling, autophagy regulation via the TRAF6–Akt–mTOR pathway, and oncogenic contexts including androgen receptor signaling in prostate cancer.

Recombinant Human FKBP5 Protein (rp367720) provides a well-defined, active protein reagent for biochemical characterization, protein–protein interaction studies, and screening assays targeting the FKBP51 TPR domain or FK1/FK2 binding pockets.

Materials and Equipment Required

• Recombinant Human FKBP5 Protein (rp367720, Aladdin Scientific)
• Sterile, nuclease-free water or manufacturer-recommended reconstitution buffer (typically PBS pH 7.4 with 10–50% glycerol as carrier)
• Low-protein-binding microcentrifuge tubes (1.5 mL)
• Calibrated micropipettes and sterile tips
• Benchtop microcentrifuge (≥10,000 × g capacity)
• UV-Vis spectrophotometer or BCA/Bradford protein assay kit for concentration verification
• SDS-PAGE and Western blot apparatus (for quality verification)
• Anti-FKBP5 antibody (for Western blot confirmation)
• Ice bucket and dry-ice/ethanol bath for aliquoting
• -80 °C freezer for long-term storage

Note: Consult the Certificate of Analysis (CoA) supplied with lot rp367720 for formulation-specific buffer composition, protein concentration, and purity data before beginning.

Step-by-Step Protocol: Reconstitution, Quality Check, and Storage

Step 1 – Thawing and Initial Centrifugation

Remove the vial from -80 °C storage and allow it to thaw on ice (approximately 10–15 minutes). Do not thaw at room temperature or in a 37 °C water bath, as this may reduce protein activity. Once thawed, briefly centrifuge the vial (1,000–2,000 × g, 30 seconds) to collect any condensate from the cap and walls.

Step 2 – Reconstitution (if lyophilized)

If the product is supplied as a lyophilized powder, reconstitute by adding the volume of sterile reconstitution buffer specified in the CoA directly to the vial. Gently pipette up and down — do not vortex. Allow the solution to sit on ice for 5 minutes, then pipette gently again to ensure complete dissolution. The recommended stock concentration is typically 0.1–1.0 mg/mL; refer to the CoA for the lot-specific recommendation.

Step 3 – Protein Concentration Verification

Measure absorbance at 280 nm using a UV-Vis spectrophotometer, or use a colorimetric assay (BCA or Bradford) against a BSA standard curve. Record the measured concentration and compare against the CoA-stated value. Accept the lot if the measured value is within ±15% of the stated concentration.

Step 4 – SDS-PAGE Quality Verification

Run 1–2 μg of protein under reducing conditions on a 10–12% SDS-PAGE gel. Stain with Coomassie Blue or silver stain. FKBP5 has a predicted molecular weight of approximately 51 kDa; the recombinant form may migrate slightly differently depending on the expression tag and glycosylation state. Verify a predominant band at the expected molecular weight with ≥90% purity as the quality acceptance criterion.

Step 5 – Aliquoting and Storage

Prepare single-use aliquots in low-protein-binding tubes to avoid repeated freeze-thaw cycles. Snap-freeze aliquots in a dry-ice/ethanol bath and store at -80 °C. For short-term use (≤1 week), aliquots may be stored at 4 °C. Addition of a carrier protein (e.g., 0.1% BSA) is recommended if the working concentration falls below 10 μg/mL to minimize adsorptive losses.

Recommended Downstream Applications and Working Concentrations

Biochemical Binding Assays (e.g., SPR, ITC, FP)

Use purified recombinant FKBP5 at concentrations typically ranging from 0.1–10 μM, depending on the expected K_d of the ligand or binding partner under investigation. Ensure buffer compatibility with the assay platform.

ELISA (Antigen Coating or Capture)

Coat FKBP5 protein at 0.5–2 μg/mL in carbonate buffer (pH 9.6) overnight at 4 °C. Block with 1–5% BSA or 5% non-fat milk in PBS-T. Validate coating efficiency with an anti-FKBP5 detection antibody.

Western Blot Positive Control

Load 50–200 ng of recombinant FKBP5 per lane as a positive control alongside cell lysates. Transfer to PVDF membrane and probe with a validated anti-FKBP5 primary antibody.

Co-Immunoprecipitation (Co-IP) and Pull-Down Assays

Use 1–5 μg of recombinant FKBP5 per reaction as bait or prey protein to study interactions with Hsp90, glucocorticoid receptors, or small-molecule inhibitors targeting the TPR or FK-domain binding pocket.

Cell-Free Functional Assays

For peptidyl-prolyl isomerase (PPIase) activity assays, use a chymotrypsin-coupled assay with a proline-containing peptide substrate. Refer to established biochemical protocols for substrate and enzyme concentrations.

Troubleshooting and Critical Notes

Problem	Likely Cause	Recommended Action
No band on SDS-PAGE at expected MW	Protein degradation due to improper thawing or repeated freeze-thaw	Use fresh aliquot; thaw on ice only; verify storage conditions
Multiple bands or smearing	Proteolytic degradation; aggregation	Add protease inhibitor cocktail to working buffer; centrifuge at 10,000 × g for 10 min before use
Low binding signal in ELISA or SPR	Protein loss due to adsorption at low concentration; incorrect buffer	Add 0.1% BSA carrier; verify buffer pH and ionic strength; increase coating concentration
Reduced PPIase activity	Protein inactivation; presence of inhibitory compounds in buffer	Prepare fresh aliquot; use freshly prepared assay buffer free of reducing agents that may disrupt disulfide bonds
Inconsistent results between lots	Lot-to-lot variation in activity or purity	Always titrate new lots; request CoA and compare QC data

General Tip: Centrifuge the protein solution at 10,000–14,000 × g for 5–10 minutes at 4 °C immediately before use to remove any aggregates that may have formed during storage or handling.

Frequently asked questions

What is the recommended reconstitution buffer for Recombinant Human FKBP5 Protein (rp367720)?

The reconstitution buffer and volume are specified in the Certificate of Analysis (CoA) supplied with each lot. Typically, sterile PBS (pH 7.4) supplemented with 10–50% glycerol as a cryoprotectant is used. Always refer to the lot-specific CoA for the exact formulation before reconstitution.

How should I store Recombinant Human FKBP5 Protein to maintain activity?

Prepare single-use aliquots immediately after reconstitution and snap-freeze them in a dry-ice/ethanol bath before storing at -80 °C for long-term use. Repeated freeze-thaw cycles should be strictly avoided as they can lead to protein aggregation and loss of activity. For short-term use within one week, aliquots may be kept at 4 °C.

What downstream applications is Recombinant Human FKBP5 Protein suitable for?

Recombinant Human FKBP5 Protein is suitable for biochemical binding assays (SPR, ITC, fluorescence polarization), ELISA antigen coating, Western blot positive controls, co-immunoprecipitation and pull-down assays, and cell-free PPIase activity assays. It is particularly valuable for studying glucocorticoid receptor co-chaperone interactions and for screening small-molecule inhibitors targeting the FKBP51 TPR or FK-domain binding pockets.

Why might I observe multiple bands or a smear on SDS-PAGE for FKBP5 protein?

Multiple bands or smearing typically indicate proteolytic degradation or protein aggregation. To prevent this, include a protease inhibitor cocktail in all working buffers and centrifuge the protein at 10,000 × g for 10 minutes at 4 °C immediately before use to remove pre-formed aggregates. Ensure the protein has not undergone repeated freeze-thaw cycles.

What is the biological significance of FKBP5 and why is it an important research target?

FKBP5 (FKBP51) is a key co-chaperone that regulates glucocorticoid receptor (GR) sensitivity by inhibiting GR nuclear translocation, thereby modulating the hypothalamic-pituitary-adrenal (HPA) axis stress response. Dysregulation of FKBP5 has been linked to PTSD, major depressive disorder, glucocorticoid resistance, and cancer. Its druggable FK1 and TPR domains make it an attractive target for small-molecule inhibitor development in psychiatric and oncology research.

References

1. Binder EB. The role of FKBP5, a co-chaperone of the glucocorticoid receptor in the pathogenesis and therapy of affective and anxiety disorders. Psychoneuroendocrinology. 2009;34 Suppl 1:S186-95. doi:10.1016/j.psyneuen.2009.05.021
2. Scharf SH, Liebl C, Binder EB, Schmidt MV, Muller MB. Expression and regulation of the Fkbp5 gene in the adult mouse brain. PLoS One. 2011;6(2):e16686. doi:10.1371/journal.pone.0016686
3. Gaali S, Kirschner A, Cuboni S, et al. Selective inhibitors of the FK506-binding protein 51 by induced fit. Nat Chem Biol. 2015;11(1):33-7. doi:10.1038/nchembio.1699
4. Stechschulte LA, Bhatt S, Martinez C, et al. FKBP51 Null Mice Are Resistant to Diet-Induced Obesity and the PPARγ Agonist Rosiglitazone. Endocrinology. 2016;157(10):3888-3900. doi:10.1210/en.2016-1205

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.