The Roles of Valine 208 and Histidine 211 in Ligand Binding and Receptor Function of the Ovine Mel1aβMelatonin Receptor

Conway, Shaun; Canning, Sarah J.; Barrett, Perry; Guardiola‐Lemaître, B.; Delagrange, P; Morgan, Peter J.

doi:10.1006/bbrc.1997.7482

Cited by 59 publications

(47 citation statements)

References 25 publications

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“…This is despite the presence of a histidine residue in transmembrane domain 5 of the receptor that has been demonstrated to be a key amino acid for the binding of melatonin in the MT1 receptor (Conway et al 1997). We and others have previously noted high-level expression of GPR50 in the ependymal layer of rodent species (Drew et al 1998, Vassilatis et al 2003.…”

Section: Introductionmentioning

confidence: 87%

Photoperiodic regulation of cellular retinoic acid-binding protein 1, GPR50 and nestin in tanycytes of the third ventricle ependymal layer of the Siberian hamster

Barrett

Ivanova

Graham

et al. 2006

Journal of Endocrinology

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Tanycytes in the ependymal layer of the third ventricle act both as a barrier and a communication gateway between the cerebrospinal fluid, brain and portal blood supply to the pituitary gland. However, the range, importance and mechanisms involved in the function of tanycytes remain to be explored. In this study, we have utilized a photoperiodic animal to examine the expression of three unrelated gene sequences in relation to photoperiod-induced changes in seasonal physiology and behaviour. We demonstrate that cellular retinoic acid-binding protein 1 (CRBP1), a retinoic acid transport protein, GPR50, an orphan G-protein-coupled receptor and nestin, an intermediate filament protein, are down-regulated in short-day photoperiods. The distribution of the three sequences is very similar, with expression located in cells with tanycyte morphology in the region of the ependymal layer where tanycytes are located. Furthermore, CRBP1 expression in the ependymal layer is shown to be independent of a circadian clock and altered testosterone levels associated with testicular regression in short photoperiod. Pinealectomy of Siberian hamsters demonstrates CRBP1 expression is likely to be dependent on melatonin output from the pineal gland. This provides evidence that tanycytes are seasonally responsive cells and are likely to be an important part of the mechanism to facilitate seasonal physiology and behaviour in the Siberian hamster.

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Section: Introductionmentioning

confidence: 87%

Photoperiodic regulation of cellular retinoic acid-binding protein 1, GPR50 and nestin in tanycytes of the third ventricle ependymal layer of the Siberian hamster

Barrett

Ivanova

Graham

et al. 2006

Journal of Endocrinology

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100

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“…However, the receptor does not bind melatonin (13,20) despite the presence of a conserved histidine residue in transmembrane domain 5 of the receptor, which is a key amino acid for binding of melatonin to MT 1 (9). Although the physiological function of GPR50 remains unknown, in situ hybridization studies on mouse, rat, and hamster brain sections have demonstrated an expression of the receptor in several areas associated with energy metabolism, namely the dorsomedial hypothalamic nucleus (DMN), lateral hypothalamus, and arcuate nucleus (12).…”

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confidence: 99%

Altered metabolism in the melatonin-related receptor (GPR50) knockout mouse

Ivanova

Bechtold

Dupré

et al. 2008

American Journal of Physiology-Endocrinology and Metabolism

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Ivanova EA, Bechtold DA, Dupré SM, Brennand J, Barrett P, Luckman SM, Loudon AS. Altered metabolism in the melatoninrelated receptor (GPR50) knock out mouse. Am J Physiol Endocrinol Metab 294: E176-E182, 2008. First published October 23, 2007 doi:10.1152/ajpendo.00199.2007.-The X-linked orphan receptor GPR50 shares 45% homology with the melatonin receptors, yet its ligand and physiological function remain unknown. Here we report that mice lacking functional GPR50 through insertion of a lacZ gene into the coding sequence of GPR50 exhibit an altered metabolic phenotype. GPR50 knockout mice maintained on normal chow exhibit lower body weight than age-matched wild-type littermates by 10 wk of age. Furthermore, knockout mice were partially resistant to dietinduced obesity. When placed on a high-energy diet (HED) for 5 wk, knockout mice consumed significantly more food per unit body weight yet exhibited an attenuated weight gain and reduced body fat content compared with wild-type mice. Wheel-running activity records revealed that, although GPR50 knockout mice showed no alteration of circadian period, the overall levels of activity were significantly increased over wild types in both nocturnal and diurnal phases. In line with this, basal metabolic rate (O 2 consumption, CO2 production, and respiratory quotient) was found to be elevated in knockout mice. Using in situ hybridization (wild-type mice) and ␤-galactosidase activity (from LacZ insertion element in knockout mice), brain expression of GPR50 was found to be restricted to the ependymal layer of the third ventricle and dorsomedial nucleus of the hypothalamus. GPR50 expression was highly responsive to energy status, showing a significantly reduced expression following both fasting and 5 wk of HED. These data implicate GPR50 as an important regulator of energy metabolism. dorsomedial hypothalamus; metabolic rate; obesity; tanycyte THE ORPHAN MELATONIN RELATED receptor (GPR50) shares ϳ45% homology with melatonin receptors MT 1 and MT 2 (20). However, the receptor does not bind melatonin (13,20) despite the presence of a conserved histidine residue in transmembrane domain 5 of the receptor, which is a key amino acid for binding of melatonin to MT 1 (9). Although the physiological function of GPR50 remains unknown, in situ hybridization studies on mouse, rat, and hamster brain sections have demonstrated an expression of the receptor in several areas associated with energy metabolism, namely the dorsomedial hypothalamic nucleus (DMN), lateral hypothalamus, and arcuate nucleus (12). Although the extent and distribution of GPR50 exhibits some degree of species specificity, high levels of expression are consistently observed in the ependymal layer of the third ventricle (12, 25).Recently, we have shown that ependymal GPR50 expression in the seasonally breeding Siberian hamster is strongly modulated by photoperiod, in which expression is greatly reduced following exposure to short photoperiods (1). Prolonged exposure to short photoperiods leads to a dramatic reduction in ...

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“…It should be noted, however, that these studies were not designed to yield any information on the contribution of the conserved residues toward ligand binding. Indeed His 5.46 is conserved in both melatonin receptors and in the melatonin-related receptor and has been previously shown to be involved in ligand binding within the melatonin mt 1 receptor (7,8). Our findings do, however, suggest that any further site-directed mutagenesis studies that are designed to investigate possible ligand binding residues in STM2, 3, or 5 of melatonin receptors should concentrate on the residues that are conserved with the melatonin-related receptor.…”

Section: Discussionmentioning

confidence: 57%

“…During the cloning of the melatonin receptors a homologue, the melatonin-related receptor, was identified, but despite containing 57% amino acid sequence identity with the TM 1 domains of the melatonin mt 1 receptor, it did not bind 2-[ 125 I]iodomelatonin or melatonin (5, 6). The melatonin-related receptor remains an orphan GPCR with no ligand or signal transduction pathway yet identified.The molecular structure and function of the melatonin mt 1 receptor has been investigated by site-directed mutagenesis, identifying the conserved His residue within TM5 as interacting with the 5-methoxy group of melatonin (7,8). Using the nomenclature of Ballesteros and Weinstein (9), this residue is located at position 5.46 (His 5.46 ), which corresponds to a position identified in the binding site of many other rhodopsin-like GPCRs, including Ser 5.46 (amino acid 207) in the hamster ␤ 2 adrenergic receptor (10).…”

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confidence: 99%

Chimeric Melatonin mt1 and Melatonin-related Receptors

Conway¹,

Drew²,

Mowat³

et al. 2000

Journal of Biological Chemistry

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Melatonin receptors bind and become activated by melatonin. The melatonin-related receptor, despite sharing considerable amino acid sequence identity with melatonin receptors, does not bind melatonin and is currently an orphan G protein-coupled receptor. To investigate the structure and function of both receptors, we engineered a series of 14 chimeric receptor constructs, allowing us to determine the relative contribution of each transmembrane domain to ligand binding and receptor function. Results identified that when sequences encoding transmembrane domains 1, 2, 3, 5, or 7 of the melatonin mt 1 receptor were replaced by the corresponding domains of the melatonin-related receptor, the resultant chimeric receptors all displayed specific 2-[ 125 I]iodomelatonin binding. Replacement of sequences incorporating transmembrane domains 4 or 6, however, resulted in chimeric receptors that displayed no detectable 2-[ 125 I]iodomelatonin binding. The subsequent testing of a "reverse" chimeric receptor in which sequences encoding transmembrane domains 4 and 6 of the melatonin-related receptor were replaced by the corresponding melatonin mt 1 receptor sequences identified specific 2-[ 125 I]iodomelatonin binding and melatoninmediated modulation of cyclic AMP levels. To further investigate these findings, site-directed mutagenesis was performed on residues within transmembrane domain 6 of the melatonin mt 1 receptor. This identified Gly 258 (Gly 6.55 ) as a critical residue required for high affinity ligand binding and receptor function.Melatonin is the native ligand for high affinity G proteincoupled melatonin receptors (1, 2). There are now almost 20 reported melatonin receptor sequences, which have been classified into three molecular subtypes, mt 1 , MT 2 , and Mel1c (3). Despite classification as molecular subtypes, they all have essentially identical binding affinities for melatonin (K i ϭ ϳ0.5 nM), and each mediates inhibition of stimulated cyclic AMP levels, mainly but not exclusively via the activation of G i proteins (4). During the cloning of the melatonin receptors a homologue, the melatonin-related receptor, was identified, but despite containing 57% amino acid sequence identity with the TM 1 domains of the melatonin mt 1 receptor, it did not bind 2-[ 125 I]iodomelatonin or melatonin (5, 6). The melatonin-related receptor remains an orphan GPCR with no ligand or signal transduction pathway yet identified.The molecular structure and function of the melatonin mt 1 receptor has been investigated by site-directed mutagenesis, identifying the conserved His residue within TM5 as interacting with the 5-methoxy group of melatonin (7,8). Using the nomenclature of Ballesteros and Weinstein (9), this residue is located at position 5.46 (His 5.46 ), which corresponds to a position identified in the binding site of many other rhodopsin-like GPCRs, including Ser 5.46 (amino acid 207) in the hamster ␤ 2 adrenergic receptor (10). Ligand binding to the ␤ 2 adrenergic receptor has also been shown to involve an ionic interaction ...

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The Roles of Valine 208 and Histidine 211 in Ligand Binding and Receptor Function of the Ovine Mel1aβMelatonin Receptor

Cited by 59 publications

References 25 publications

Photoperiodic regulation of cellular retinoic acid-binding protein 1, GPR50 and nestin in tanycytes of the third ventricle ependymal layer of the Siberian hamster

Photoperiodic regulation of cellular retinoic acid-binding protein 1, GPR50 and nestin in tanycytes of the third ventricle ependymal layer of the Siberian hamster

Altered metabolism in the melatonin-related receptor (GPR50) knockout mouse

Chimeric Melatonin mt1 and Melatonin-related Receptors

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