Phos binding reagent (Phosbind) acrylamide

Phosbind Acrylamide is an innovative phosphate-binding reagent. It appears as a yellow viscous oil and is an acrylamide derivative functionalized with a Phosbind ligand. It is also a bicyclic metal complex, specifically designed for the electrophoretic separation and detection of phosphorylated and non-phosphorylated proteins. In the presence of divalent metal ions such as Mn²⁺ or Zn²⁺, the reagent specifically recognizes and binds to phosphate groups, with optimal reaction conditions at neutral physiological pH 6–8.

The mechanism of Phosbind Acrylamide relies on its specific interaction with phosphate groups. After the reagent is added to a conventional SDS-PAGE separating gel together with divalent metal ions such as Mn²⁺ or Zn²⁺, the Phosbind Acrylamide–metal ion complex immobilized in the gel specifically binds to phosphate groups on proteins. This reduces the electrophoretic mobility of phosphorylated proteins, while the migration of non-phosphorylated proteins remains unaffected, thereby achieving separation between the two forms. Moreover, the higher the phosphorylation level of a protein, the slower its migration rate. The typical molar ratio of Phosbind Acrylamide to metal ions is 1:2, although exceptions may occur in practical applications.

This product has a wide range of applications. It can be used for qualitative and quantitative detection of phosphorylation levels in in vitro kinase and phosphatase reaction systems, analysis of endogenous protein phosphorylation, plant protein phosphorylation studies, phosphorylation status identification, and phosphoproteomics research. It also enables fine separation of phosphorylated isoforms in two-dimensional electrophoresis. Additionally, it is suitable for drug screening and target validation, studies of cell signaling pathways (e.g., GPCR, Wnt, MAPK), as well as fundamental research areas including neuroscience, metabolic regulation, apoptosis, and DNA damage repair.

This product is suitable for detecting proteins in the range of 5–350 kDa, with no limitations regarding species (human, animal, plant, microorganism, etc.) or sample type (purified protein, cell lysate, tissue homogenate, in vitro kinase reaction system, etc.). It is compatible with various downstream analysis methods, including CBB staining, Western blotting (WB), two-dimensional electrophoresis, and mass spectrometry (MS). Compared with traditional phosphorylation detection methods, this technology allows direct visualization of phosphorylation-dependent electrophoretic mobility shifts without the need for specific phospho-antibodies. For optimal experimental results, the use of the following recommended accessories is advised: Prestained Protein Marker (F4005), Protease Inhibitor Cocktail (K1007), Phosphatase Inhibitor Cocktail (K1015), and Tris-Gly Fixed-Concentration Gel Preparation Kits (K4131–K4135, 6%/8%/10%/12%/15%).

This product consists of Phosbind Acrylamide and a separately packaged tube of MnCl₂. Using a standard Mini PAGE gel (8.3 cm × 7.3 cm, 1 mm thickness) with a separating gel volume of 5 mL and a final Phosbind Acrylamide concentration of 50 μM as an example, one 5 mg vial of the product can prepare approximately 33 gels. The number of gels that can be prepared varies depending on the concentration of Phosbind Acrylamide used; higher concentrations yield fewer gels.

·No phospho-antibody required: Particularly suitable for studying phosphorylation sites lacking commercial antibodies, and offers a more cost-effective solution.
·Excellent separation performance: Enables fine separation and simultaneous detection of non-phosphorylated proteins and proteins with different phosphorylation levels on the same membrane.
·Complete kit: Supplied with sufficient high-quality MnCl₂; no additional purchase required.
·High affinity: Exhibits high specificity and high affinity for any phosphorylated group on proteins.
·High safety: Free of radioactive elements, chemical labels, and fluorescent markers.
·Broad applicability: No species or sample type restrictions; recognizes all phosphorylation forms at Ser, Thr, and Tyr residues.
·High sensitivity: Detection limit reaches the ng level, which can be further enhanced by using high-sensitivity chemiluminescent substrates.
·Easy operation: The workflow is essentially the same as conventional SDS-PAGE, requiring no additional specialized equipment.
·Strong compatibility: Compatible with various downstream analyses, including CBB staining, Western blotting, two-dimensional electrophoresis, and mass spectrometry (MS).

[1] M. J. Hubbard, P. Cohen. On target with a new mechanism for the regulation of protein phosphorylation. Trends Biochem. Sci. 18: 172 (1993).

[2] B. Agnew et al. Compositions and methods for detection and isolation of phosphorylated molecules. US Patent # 7,102,005. (September 5, 2006).

Q: Product (F4002) – How many gels can be prepared?

A: Based on a Mini PAGE gel (8.3 cm × 7.3 cm, 1 mm thick) with a 50 μM Phosbind separating gel (5 mL/gel), 10 mg yields 3.3 mL of stock solution. Using 0.05 mL of Phosbind per gel at 50 μM, approximately 66 gels can be prepared; 5 mg yields about 33 gels. The number varies with Phosbind concentration — higher concentration, fewer gels.

Q: Storage conditions for product (F4002)

A: Phosbind acrylamide (F4002) is a yellow oil. Store at 4°C protected from light for up to 1 year. Prepared stock solutions can be stored at 4°C protected from light for at least 3 months. Mn²⁺-Phosbind gels should be freshly prepared.

Q: What are the applications of Phosbind?

A: Suitable for purified proteins, cell lysates, in vitro kinase reactions, and various sample types (animal, plant, microbial). Compatible with Mn²⁺ or Zn²⁺ systems. Enables phosphoprotein detection without specific antibodies, supporting downstream analyses such as CBB staining, Western blotting, 2D electrophoresis, and mass spectrometry. Works with standard electrophoresis, transfer, and imaging equipment.

Q: Is Phosbind (F4002) suitable for tagged proteins (e.g., His, GFP), in vitro kinase assays, multi-band proteins (e.g., Erk), and mutant phosphoprotein detection?

A: Fully suitable. In vitro kinase reaction mixtures can be directly loaded without special purification.

Q: What is the molecular weight range for Phosbind?

A: Works well for proteins in the 30–130 kDa range, with reported successful separation of proteins up to 350 kDa.

Q: What are the advantages of Phosbind over traditional phosphodetection methods (e.g., phospho-antibodies, radiolabeling)?

A: ① Non-radioactive, safe; ② No phospho-specific antibodies needed, detects all phosphorylation sites; ③ Resolves differentially phosphorylated isoforms; ④ Simple, compatible with standard SDS-PAGE workflows.

Q: Which amino acid phosphorylations can Phosbind detect?

A: Phosbind specifically binds phosphate groups on all phosphorylated amino acids (pSer, pThr, pTyr, etc.), independent of amino acid type or sequence.

Q: What is the detection sensitivity of Phosbind?

A: ng-level sensitivity; can be further enhanced with high-sensitivity chemiluminescent substrates.

Q: Can Phosbind distinguish the number of phosphate groups on a protein?

A: Yes, it distinguishes different phosphorylation levels — more phosphate groups result in slower migration, producing multiple resolved bands. However, it cannot determine the exact number of phosphorylation sites per protein; mass spectrometry is required for that.

Q: Can Phosbind be used for DNA analysis?

A: Yes, for detecting and separating DNA phosphorylation sites (e.g., 5'-end phosphorylated DNA, phosphorylated oligonucleotides), based on the same phosphate-binding principle as for proteins.

Q: What are the main Phosbind series products and their applications?

A: Three main products: Phosbind acrylamide (F4002) and Phosbind Biotin series (F4001, F4004). F4002 is used to prepare SDS-PAGE gels for separating phosphorylated from non-phosphorylated proteins, followed by detection with non-phospho primary antibodies. The Biotin series (F4001/F4004) are used after transfer to PVDF membranes with streptavidin-HRP for antibody-free detection. F4004 has a longer linker for higher sensitivity; F4001 has better solubility — F4001 is recommended first.

Q: How to choose between Mn²⁺-Phosbind and Zn²⁺-Phosbind systems?

A: ① Mn²⁺: Compatible with standard Tris-Glycine buffers, easier to use, more widely reported — first choice. ② Zn²⁺: Neutral Bis-Tris gel system, higher binding affinity, suitable for difficult-to-resolve or high-molecular-weight proteins (>200 kDa).

Q: What quality control guarantees are there for Phosbind products?

A: Every batch undergoes strict QC: ① Purity testing; ② Activity validation using standard samples (e.g., dephosphorylated α-casein); ③ Stability testing under different storage conditions; ④ QC report included with each batch for traceability and reproducibility.

Q: What are the key steps and precautions for preparing Phosbind SDS-PAGE gels?

A: ① Add Phosbind acrylamide and metal ions (Mn²⁺ or Zn²⁺, typically 1:2 molar ratio) to the separating gel. Try Phosbind concentrations from 20–50–100 μM. ② Mn²⁺ gels should be freshly prepared; Zn²⁺ gels can be stored at 4°C protected from light for up to 3 months. ③ Avoid EDTA, high concentrations of detergents (e.g., SDS), and inorganic salts.

Q: How to optimize sample loading and gel concentration?

A: ① Loading: 1–5 μg for purified protein, 10–30 μg for cell/tissue lysates (adjust based on expression). ② Gel concentration: 8% for <60 kDa, 6% for >60 kDa; for >200 kDa, add 3–5% agarose to increase gel strength. ③ Phosbind concentration: Titrate from 20 μM up to 50–100 μM; use the lowest concentration that gives good separation.

Q: Cloudiness when preparing Phosbind stock solution — is it normal? Can water be used directly?

A: Cloudiness is normal due to methanol; let it sit to clear. For stock preparation, dissolve in methanol first, then add water. Using water alone makes dissolution difficult and slow. If insoluble material remains, centrifuge and use the supernatant.

Q: How to choose a protein marker? Can it clearly indicate molecular weights?

A: Use an EDTA-free protein marker (e.g., F4005) to avoid band distortion. The marker in Phosbind results only indicates transfer efficiency; it cannot be used to accurately infer sample protein molecular weights due to phosphorylation-induced mobility shifts.

Q: Does ATP used in in vitro phosphorylation reactions affect electrophoresis results?

A: ATP itself carries phosphate groups. At 2.0 mM, it has no special effect. Concentrations above 5 mM may compete for Phosbind binding or interfere with gel polymerization. Dialysis or precipitation to remove ATP is recommended before loading.

Q: What are the special steps for Phosbind Western blot transfer?

A: After electrophoresis, the gel must be washed with transfer buffer or running buffer containing 1–10 mM EDTA for 10 minutes, 1–3 times, to remove metal ions and improve transfer efficiency. After transfer, follow standard WB procedures. Wet transfer and PVDF membranes are recommended.

Q: What causes band distortion with Phosbind and how to fix it?

A: ① Sample contains EDTA/salts/detergents: TCA precipitation or dialysis. ② Viscous sample: Boil thoroughly or dilute. ③ Acidic sample (yellow/orange after loading buffer): Neutralize with Tris to blue-purple. ④ Prestained marker contains EDTA: Switch to EDTA-free marker (e.g., F4005). ⑤ Empty lanes: Add equal volume of loading buffer to empty lanes to avoid gradient artifacts.

Q: What causes smearing or severe trailing and how to fix it?

A: Protein degradation (inactive protease inhibitors), incomplete solubilization (particulates), insufficient SDS in running buffer, uneven gel polymerization, excessive Phosbind or Mn²⁺ concentration, or high temperature/fast electrophoresis. Solutions: fully lyse and centrifuge samples, use fresh inhibitors and running buffer, optimize conditions with cooling, and titrate Phosbind/Mn²⁺ concentrations.

Q: What causes weak or no phosphoprotein signal and how to fix it?

A: Low phosphorylation levels (often reversible), insufficient sample amount, inadequate sample protection (insufficient or inactive phosphatase inhibitors), poor transfer efficiency, inappropriate blocking conditions, or poor antibody quality. Solutions: increase sample amount, optimize sample handling and pre-transfer washing, use high-quality antibodies and appropriate blocking. Ensure thorough EDTA treatment before transfer.

Q: What causes difficult transfer and how to fix it?

A: ① Mn²⁺ not removed before transfer: Wash thoroughly with EDTA-containing transfer/running buffer. ② Gel too stiff: Reduce acrylamide concentration or methanol concentration.

Q: What causes high background or multiple nonspecific bands and how to fix it?

A: Similar to standard Western blot — excessive primary/secondary antibody, insufficient blocking, inadequate washing, poor antibody specificity, or improper PVDF membrane handling. Solutions: reduce antibody concentrations, optimize blocking and washing conditions, use highly specific antibodies.

Q: What causes multiple bands and what do you suggest?

A: May result from different phosphorylation levels or protein degradation. Run a parallel SDS-PAGE gel without Phosbind to rule out degradation.

Q: What causes phosphoprotein bands not shifting as expected or showing little difference from regular gels, and how to fix it?

A: ① EDTA treatment omitted or insufficient, preventing efficient transfer. ② Phosbind or Mn²⁺ concentration too low to cause a clear mobility shift. ③ Target protein has few phosphorylation sites or low modification levels. ④ Gel concentration too low for proper separation. Solutions: ① Thorough EDTA pre-treatment before transfer. ② Optimize Phosbind/Mn²⁺ concentrations. ③ Increase loading or stimulate cells to enhance phosphorylation. ④ Use appropriate gel concentration.

Q: Phosbind gels are fragile, especially for high-molecular-weight proteins — what to do?

A: Phosbind gels are more fragile than regular gels due to the added Phosbind and MnCl₂. For low-concentration gels (e.g., for high-MW proteins), add 0.5% agarose to increase mechanical strength.

Q: How to verify poor separation between phosphorylated and non-phosphorylated proteins?

A: ① Use a positive control (e.g., mixture of phosphorylated and dephosphorylated α-casein) to confirm system performance. ② Run a parallel regular SDS-PAGE gel to rule out degradation. ③ Adjust Phosbind concentration or switch from Mn²⁺ to Zn²⁺ system. ④ Treat samples with λ protein phosphatase — if the shifted bands disappear, it strongly confirms phosphorylation.

Positive control reference:

Q: What are the suggested experimental controls?

A:

 
Q: Can Phosbind (F4002) be used with a pre-made gel kit (Tris-Glycine system)?

A: Yes, it can be used with our Tris-Glycine fixed-concentration gel kits (K4131–K4135: 6%/8%/10%/12%/15%). For other brands of gel kits, we recommend testing compatibility.

Q: What are the related products for Phosbind experiments?