SUMMARY G protein-coupled receptor (GPCR)-mediated signal transduction is central to human physiology and disease intervention, yet the molecular mechanisms responsible for ligand-dependent signaling responses remain poorly understood. In Class A GPCRs, receptor activation and G protein coupling entail outward movements of transmembrane segment 6 (TM6). Using single-molecule Fluorescence Resonance Energy Transfer (smFRET) imaging, we examine TM6 motions in the β2 adrenergic receptor (β2AR) upon exposure to orthosteric ligands with different efficacies, in the absence and presence of the Gs heterotrimer. We show that partial and full agonists affect TM6 motions in a manner that differentially regulates the rate at which GDP-bound β2AR-Gs complexes are formed and the efficiency of nucleotide exchange leading to Gs activation. These data also reveal transient nucleotide-bound β2AR-Gs species distinct from known structures and single-molecule perspectives on the allosteric link between ligand and nucleotide binding pockets that shed new light on the G protein activation mechanism.
ObjectivesGPR40 (FFAR1), a clinically proven anti-diabetes target, is a Gq-coupled receptor for long chain fatty acids (LCFA) stimulating insulin secretion directly and mediating a major part of the dietary triglyceride-induced secretion of the incretins GLP-1 and GIP. In phase-II studies the GPR40 agonist TAK-875 decreased blood glucose but surprisingly without stimulating incretins.Methods and resultsHere we find that GPR40 can signal through not only Gq and IP3 but also Gs and cAMP when stimulated with certain agonists such as AM-1638 and AM-5262 in contrast to the endogenous LCFA ligands and agonists such as TAK-875 and AM-837, which only signal through Gq. In competition binding against [3H]AM-1638 and [3H]L358 the Gq + Gs and the Gq-only agonists either competed for or showed positive cooperativity by increasing the binding of the two different radio-ligands, in opposite ways. Nevertheless, both the Gq-only and the Gq + Gs agonists all docked surprisingly well into the binding site for TAK-875 in the X-ray structure of GPR40. In murine intestinal primary cell-cultures the endogenous LCFAs and the Gq-only agonists stimulated GLP-1 secretion with rather poor efficacy as compared with the high efficacy Gq + Gs GPR40 agonists and a prototype GPR119 agonist. Similarly, in fasting both male and female mice the Gq + Gs agonists showed significantly higher efficacy than the Gq-only agonists in respect of increasing plasma GLP-1 and plasma GIP in a GPR40-dependent manner.ConclusionsIt is concluded that stimulation of GPR40 by endogenous LCFAs or by Gq-only synthetic agonists result in a rather limited incretin response, whereas Gq + Gs GPR40 agonists stimulate incretin secretion robustly.
The existence of a nation-wide twin register and central psychiatric register has made possible a catamnestic investigation of an unselected and representative sample of twins with manic-depressive disorders. From a total population of 11,288 same-sexed twin pairs born 1870-1920 in Denmark 126 probands from 110 pairs were ascertained. Among the co-twins of 69 monozygotic probands there were found 46 with manic-depressive disorders, and a further 14 had presented other psychoses or marked affective personality disorders or had committed suicide, yielding a proband rate of strict concordance, C1 = 0-67 and of broad, partial concordance, C2 = 0-87. The corresponding direct pairwise concordance rates were 32/55 = 0-58 and 46/55 = 0-84 respectively. For the dizygotic twins the proband concordance rate of C1 was 11/54 = 0-20 and of C2 20/54 = 0-37, and the direct pairwise rates were 9/52 = 0-17 and 18/52 = 0-35 respectively. The differences between the pairwise rates for the monozygotic and dizgotic twins are significant (P less than 0-001 at X2 analysis). This finding is in accordance with previous twin studies of manic-depressive disorders and confirms the evidence of a strong genetic factor. The concordance with respect to unipolar and bipolar forms was not in contradiction to recent evidence of a genetic difference between the bipolar and unipolar form, the latter probably related to the female sex.
A family in which a translocation t(11; 21) (q23 ;q22) was segregating through three generations was studied clinically and cytogenetically. Individuals mono somic for the distal part of the long arm of chromosome No. 11 showed severe malformations and retardation. Apatient trisomic for this part of chromosome No. 11 was mentally retarded but less severely affected. Marker gene studies could exclude the location of several blood group loci at the distal part of the long arm of chromosome No. 11, but did not give any positive evidence of linkage to this part.
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