Human Motilin Receptor

Motilin is a 22 amino acid peptide that potently stimulates gastrointestinal contractility. The biological effects of motilin are mediated by a G_q-coupled seven transmembrane protein, currently termed motilin receptor (MR), that shares significant sequence similarity with the ghrelin receptor (Feighner et al., 1999). The motilin receptor is also activated by the antibiotic erythromycin; this interaction appears to mediate some of the gastrointestinal side effects of erythromycin. Although motilides (non-antibiotic derivatives of erythromycin) such as ABT-229 have been investigated for treatment of diabetic gastroporesis, the effectiveness has been limited by tachyphylaxis (decreased response to ligand) resulting from receptor downregulation (Thielemans et al., 2005). Agonists of the motilin receptor with reduced densensitization activity remain a potential treatment for disorders of gastric motility. Chemicon′s cloned human Motilin Receptor-expressing cell line is made in the Chem-1 host, which supports high levels of recombinant Motilin Receptor expression on the cell surface and contains high levels of the promiscuous G protein Gα15 to couple the receptor to the calcium signaling pathway. Thus, the cell line is an ideal tool for screening for antagonists of interactions between the Motilin Recptor and its ligands. Chemicon′s motilin 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 motilin receptor interactions with motilin. The membrane preparations exhibit a Kd of 0.43nM for [¹²⁵I]-Motilin. With 5.0 µg/well Motilin Membrane Prep and 0.5 nM [¹²⁵I]-Motilin, a greater than 30-fold signal-to-background ratio was obtained.

Radioligand binding assay, and GTPγS binding.

GPCR Class: A

Protein Target: motilin receptor / MTLR / GPR38

Target Sub-Family: Motilin

Signal:background and specific binding values obtained in a competition binding assay with varying amounts of Motilin Receptor membrane prep:

	5 µg/well	10 µg/well
Signal:Background	75	65
Specific Binding (cpm)	46348	54457

SPECIFICATIONS: 1 unit = 5 µg membrane preparation
Bmax: 5.6 pmol/mg
Kd: 0.43 nM

Inucbation Conditions
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, a GF/C 96-well filter plate 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, filtered and stored at 4°C
Radioligand: [125I] Motilin (Perkin Elmer # NEX378)
Wash Buffer: 50 mM Hepes, pH 7.4, 500mM 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 30-fold signal:background with ¹²⁵I-labeled motilin at 0.5 nM.

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

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

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