Overview of CENPB and Biological Significance

Centromere Protein B (CENPB) is a constitutive centromere protein that plays a fundamental role in maintaining centromere identity and chromosomal stability in mammalian cells. It is a sequence-specific DNA-binding protein that recognizes and binds to the 17-bp CENP-B box motif present within alpha-satellite DNA arrays at centromeres. CENPB contains an N-terminal DNA-binding domain homologous to the helix-turn-helix motif found in certain transposases, as well as a C-terminal dimerization domain.

Recombinant Human CENPB Protein (SKU: rp365907) enables researchers to study centromere assembly mechanisms, nucleosome positioning, and kinetochore architecture in vitro. It is also a valuable tool in chromatin reconstitution experiments, electrophoretic mobility shift assays (EMSA), and structural studies aimed at elucidating the molecular basis of centromere specification.

Reconstitution and Storage Conditions

Reconstitution: Briefly centrifuge the vial at 6,000–10,000 × g for 30 seconds before opening to collect any lyophilized material from the walls and cap. Reconstitute the protein in sterile, deionized water or in the buffer recommended in the product datasheet to the desired stock concentration (typically 0.1–1.0 mg/mL). Gently pipette to mix; avoid vortexing, which can cause protein aggregation and denaturation.

Buffer compatibility: CENPB is generally compatible with PBS (pH 7.4) or Tris-HCl–based buffers (20–50 mM, pH 7.5) supplemented with 150 mM NaCl, 10% glycerol, and 1 mM DTT to maintain reducing conditions and prevent aggregation. Avoid buffers containing strong detergents incompatible with downstream assays.

Storage: Aliquot the reconstituted protein into single-use volumes to minimize freeze-thaw cycles. Store aliquots at -80°C for long-term use (up to 12 months) or at -20°C for short-term use (up to 1 month). Thaw on ice immediately before use. Repeated freeze-thaw cycles (more than 2–3) should be strictly avoided, as they significantly reduce protein activity and may cause aggregation.

Quality Control and Activity Verification

Purity assessment: Verify protein purity by SDS-PAGE under reducing conditions followed by Coomassie staining. A single dominant band at the expected molecular weight of CENPB (~80 kDa for full-length human CENPB) confirms acceptable purity. Western blot using a validated anti-CENPB antibody provides an additional identity confirmation.

Activity testing: Functional activity of the recombinant CENPB protein can be assessed by electrophoretic mobility shift assay (EMSA) using a biotinylated oligonucleotide containing the canonical 17-bp CENP-B box sequence (5′-CTTCGTTGGAAACGGGA-3′). A clear band shift relative to the free probe indicates specific DNA-binding activity. Ensure that appropriate negative controls (e.g., mutated CENP-B box or non-specific DNA) are included.

Endotoxin testing: For cell-based or in vivo applications, confirm endotoxin levels are below the acceptable threshold (typically <1.0 EU/µg protein) using a Limulus Amebocyte Lysate (LAL) assay. Consult the certificate of analysis (CoA) provided with each lot for lot-specific QC data.

Experimental Applications and Working Concentrations

Recombinant Human CENPB Protein is suitable for a range of biochemical and cell biology applications. Recommended starting concentrations are provided below; however, optimization may be required depending on the specific assay format and experimental conditions.

• EMSA / DNA-binding assays: Use 50–500 nM CENPB protein with 1–10 nM labeled CENP-B box DNA probe. Titrate protein concentration to determine the apparent dissociation constant (K_d).
• Pull-down assays: Immobilize biotinylated CENP-B box DNA on streptavidin-coated beads and incubate with 0.5–5 µg recombinant CENPB in binding buffer. Wash stringently and elute for SDS-PAGE analysis.
• Western Blot (as standard/positive control): Load 50–200 ng per lane for chemiluminescent detection.
• Chromatin reconstitution: Combine with purified core histones and alpha-satellite DNA under salt-gradient dialysis conditions to assemble CENP-B-bound nucleosomal arrays for structural studies.
• ELISA (as coating antigen or capture standard): Coat plates at 0.5–2 µg/mL in carbonate buffer (pH 9.6) overnight at 4°C.

Always include appropriate negative controls and titrate reagents to establish optimal working concentrations for your specific experimental system.

Troubleshooting Common Issues

Problem: No activity detected in EMSA.
Possible causes: Protein aggregation due to improper storage or excessive freeze-thaw; degradation; incorrect buffer conditions. Solutions: Use freshly thawed aliquots; verify protein integrity by SDS-PAGE; ensure reducing agent (DTT or β-ME) is present in the binding buffer; confirm oligonucleotide contains the correct CENP-B box sequence.

Problem: Multiple bands on SDS-PAGE (degradation).
Possible causes: Protease contamination; prolonged incubation at room temperature. Solutions: Add protease inhibitor cocktail to all buffers; keep protein on ice at all times; minimize handling time.

Problem: Protein precipitation upon reconstitution.
Possible causes: Reconstitution at too high a concentration; incompatible buffer; aggregation during freeze-thaw. Solutions: Reconstitute at lower concentration; add 10% glycerol to stabilize; centrifuge at 10,000 × g for 5 minutes to remove aggregates before use.

Problem: High background in ELISA.
Possible causes: Insufficient blocking; non-specific binding of detection antibody. Solutions: Optimize blocking conditions (e.g., 3–5% BSA or 5% non-fat milk in PBST); increase wash stringency; titrate primary and secondary antibodies.