TY - JOUR
T1 - Identification of four novel exon 5 splice variants of the mouse μ-opioid receptor gene
T2 - Functional consequences of C-terminal splicing
AU - Pan, Ying Xian
AU - Xu, Jin
AU - Bolan, Elizabeth
AU - Moskowitz, Howard S.
AU - Xu, Mingming
AU - Pasternak, Gavril W.
PY - 2005/9
Y1 - 2005/9
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=23944518698&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=23944518698&partnerID=8YFLogxK
U2 - 10.1124/mol.105.011858
DO - 10.1124/mol.105.011858
M3 - Article
C2 - 15939800
AN - SCOPUS:23944518698
SN - 0026-895X
VL - 68
SP - 866
EP - 875
JO - Molecular Pharmacology
JF - Molecular Pharmacology
IS - 3
ER -