ChemiSCREEN™ Membrane Preparation Recombinant Human BB₃ Bombesin Receptor

ChemiSCREEN™ Membrane Preparation Recombinant Human BB₃ Bombesin Receptor

ChemiScreen

Full length human BRS3 encoding BB₃

Bombesin, a bioactive peptide first identified in amphibian skin, is related to two mammalian peptides, gastrin-releasing peptide (GRP) and neuromedin B. A family of 3 GPCRs, including GRP-R (BB₁), NMB-R (BB₂) and BRS-3 (BB₃), mediate the biological effects of the peptides (Ohki-Hamazaki et al., 2005). BB₃ differs from the others by its low affinity for bombesin. Although an endogenous ligand for BB₃ has yet to be identified, a synthetic nonselective bombesin-like peptide [H-D-Phe6, β-Ala11, Phe13, Nle14]-bombesin-(6-14)-nonapeptide amide (Bombesin (6-14) Analog) activates BB₃ with high potency. BB₃-null mice have an obese phenotype (Matsumoto and Iijima, 2003). Millipore's BB₃ membrane preparations are crude membrane preparations made from our proprietary stable recombinant cell lines to ensure high-level of GPCR surface expression; thus, they are ideal HTS tools for screening of antagonists of BB₃ receptor interactions with its ligand. The membrane preparations exhibit a Kd of 0.23nM for [125I]-Bombesin (6-14) Analog. With 10 µg/well BB₃ Membrane Prep and 0.3 nM [¹²⁵I]-Bombesin (6-14) Analog, a greater than 3-fold signal-to-background ratio was obtained.

Radioligand binding assay and GTPγS binding

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Chem-1, an adherent cell line expressing the endogenous promiscuous G-protein, Gα15.

Chem-1

Liquid in packaging buffer: 50 mM Tris pH 7.4, 10% glycerol and 1% BSA with no preservatives.
Packaging method: Membranes protein was adjusted to the indicated concentration in packaging buffer, rapidly frozen, and stored at -80oC.

Table 1. Signal:background and specific binding values obtained in a competition binding assay with BB₃ membrane prep.

	10 µg/well
Signal:Background	5.2
Specific Binding (cpm)	3403

SPECIFICATIONS: 1 unit = 10 µg
Bmax 0.95 pmol/mg protein
Kd 0.3 nM

Membranes are mixed with radioactive ligand and unlabeled competitor (see Figures 1 and 2 for concentrations tested) in binding buffer in a nonbinding 96-well plate, and incubated for 1-2 h. Prior to filtration, an FC 96-well harvest plate (Millipore cat. # MAHF C1H) is coated with 0.33% polyethyleneimine for 30 min, then washed with 50mM HEPES, pH 7.4, 0.5% BSA. Binding reaction is transferred to the filter plate, and washed 3 times (1 mL per well per wash) with Wash Buffer. The plate is dried and counted.

Binding buffer: 50 mM Hepes, pH 7.4, 5 mM MgCl₂, 1 mM CaCl₂, 0.2% BSA, 0.2 mg/ml bacitracin, 20 µg/ml leupeptin, 20 µg/ml chymostatin, 1 Protease Inhibitor cocktail Tablets (Roche Cat. No. 11 873 580 001) for each 50 ml binding buffer.

Radioligand: [¹²⁵I]-Bombesin (6-14) Analog (Perkin Elmer NEX377)

Wash Buffer: 50 mM Hepes, pH 7.4, 500 mM NaCl , 0.1% BSA, filtered and stored at 4°C.

One package contains enough membranes for at least 200 assays (units), where an unit is the amount of membrane that will yield greater than 3-fold signal:background with ¹²⁵I-labeled Bombesin (6-14) Analog at 0.3 nM.

Membrane Preparations

Maintain frozen at -70°C for up to 2 years. Do not freeze and thaw.

Human