Identification of four novel exon 5 splice variants of the mouse μ-opioid receptor gene: Functional consequences of C-terminal splicing

Ying Xian Pan, Jin Xu, Elizabeth Bolan, Howard S. Moskowitz, Mingming Xu, Gavril W. Pasternak

Research output: Contribution to journalArticle

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Abstract

The rat μ-opioid receptor clone in which novel exon 5 was found in the place of exon 4 (MOR-1B) was one of the first MOR-1 variants described. We now have identified the mouse homolog of the rat MOR-1B as well as four additional variants derived from splicing from exon 3 into different sites within exon 5. The sequences of all of the variants were identical except for the intracellular tip of the C terminus encoded by exon 5, where each variant predicted a unique amino acid sequence ranging from 2 to 39 amino acids. All of the mMOR-1B variants were selective for μ-opioids in receptor-binding assays, as anticipated, because they all have identical binding pockets defined by the transmembrane domains. However, the relative potency and efficacy of μ-agonists to each other varied from variant to variant in guanosine 5′-O-(3-[35S]thio)triphosphate-binding studies, as shown by morphine-6β-glucuronide, which was the most efficacious agent against mouse MOR-1B1 (mMOR-1B1) and the least efficacious agent against mMOR-1B2. mMOR-1B4 was quite unusual. Although mMOR-1B4 was μ-selective in receptor-binding studies and antagonists labeled mMOR-1B4 well, the binding affinities of most of the μ-agonists were far lower than those seen with mMOR-1, suggesting that the 39 amino acids at the C terminus of mMOR-1B4 influences the conformation of the receptor and its ligand recognition site itself either directly or through its interactions with other proteins. In conclusion, alterations in the amino acid sequence of the C terminus do not alter the μ-specificity of the receptor but they can influence the binding characteristics, efficacy, and potency of μ-opioids.

Original languageEnglish (US)
Pages (from-to)866-875
Number of pages10
JournalMolecular Pharmacology
Volume68
Issue number3
DOIs
StatePublished - Sep 2005
Externally publishedYes

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Opioid Receptors
Exons
Genes
Amino Acid Sequence
Guanosine 5'-O-(3-Thiotriphosphate)
Amino Acids
Opioid Analgesics
Clone Cells
Ligands
Proteins

ASJC Scopus subject areas

  • Medicine(all)
  • Molecular Medicine
  • Pharmacology

Cite this

Identification of four novel exon 5 splice variants of the mouse μ-opioid receptor gene : Functional consequences of C-terminal splicing. / Pan, Ying Xian; Xu, Jin; Bolan, Elizabeth; Moskowitz, Howard S.; Xu, Mingming; Pasternak, Gavril W.

In: Molecular Pharmacology, Vol. 68, No. 3, 09.2005, p. 866-875.

Research output: Contribution to journalArticle

Pan, Ying Xian ; Xu, Jin ; Bolan, Elizabeth ; Moskowitz, Howard S. ; Xu, Mingming ; Pasternak, Gavril W. / Identification of four novel exon 5 splice variants of the mouse μ-opioid receptor gene : Functional consequences of C-terminal splicing. In: Molecular Pharmacology. 2005 ; Vol. 68, No. 3. pp. 866-875.
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abstract = "The rat μ-opioid receptor clone in which novel exon 5 was found in the place of exon 4 (MOR-1B) was one of the first MOR-1 variants described. We now have identified the mouse homolog of the rat MOR-1B as well as four additional variants derived from splicing from exon 3 into different sites within exon 5. The sequences of all of the variants were identical except for the intracellular tip of the C terminus encoded by exon 5, where each variant predicted a unique amino acid sequence ranging from 2 to 39 amino acids. All of the mMOR-1B variants were selective for μ-opioids in receptor-binding assays, as anticipated, because they all have identical binding pockets defined by the transmembrane domains. However, the relative potency and efficacy of μ-agonists to each other varied from variant to variant in guanosine 5′-O-(3-[35S]thio)triphosphate-binding studies, as shown by morphine-6β-glucuronide, which was the most efficacious agent against mouse MOR-1B1 (mMOR-1B1) and the least efficacious agent against mMOR-1B2. mMOR-1B4 was quite unusual. Although mMOR-1B4 was μ-selective in receptor-binding studies and antagonists labeled mMOR-1B4 well, the binding affinities of most of the μ-agonists were far lower than those seen with mMOR-1, suggesting that the 39 amino acids at the C terminus of mMOR-1B4 influences the conformation of the receptor and its ligand recognition site itself either directly or through its interactions with other proteins. In conclusion, alterations in the amino acid sequence of the C terminus do not alter the μ-specificity of the receptor but they can influence the binding characteristics, efficacy, and potency of μ-opioids.",
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