| Structural highlights
Function
GNAT3_HUMAN Guanine nucleotide-binding protein (G protein) alpha subunit playing a prominent role in bitter and sweet taste transduction as well as in umami (monosodium glutamate, monopotassium glutamate, and inosine monophosphate) taste transduction (PubMed:38600377, PubMed:38776963). Transduction by this alpha subunit involves coupling of specific cell-surface receptors with a cGMP-phosphodiesterase; Activation of phosphodiesterase lowers intracellular levels of cAMP and cGMP which may open a cyclic nucleotide-suppressible cation channel leading to influx of calcium, ultimately leading to release of neurotransmitter. Indeed, denatonium and strychnine induce transient reduction in cAMP and cGMP in taste tissue, whereas this decrease is inhibited by GNAT3 antibody. Gustducin heterotrimer transduces response to bitter and sweet compounds via regulation of phosphodiesterase for alpha subunit, as well as via activation of phospholipase C for beta and gamma subunits, with ultimate increase inositol trisphosphate and increase of intracellular Calcium. GNAT3 can functionally couple to taste receptors to transmit intracellular signal: receptor heterodimer TAS1R2/TAS1R3 senses sweetness and TAS1R1/TAS1R3 transduces umami taste, whereas the T2R family GPCRs such as TAS2R14 act as bitter sensors (PubMed:38600377, PubMed:38776963). Also functions as lumenal sugar sensors in the gut to control the expression of the Na+-glucose transporter SGLT1 in response to dietaty sugar, as well as the secretion of Glucagon-like peptide-1, GLP-1 and glucose-dependent insulinotropic polypeptide, GIP. Thus, may modulate the gut capacity to absorb sugars, with implications in malabsorption syndromes and diet-related disorders including diabetes and obesity.[1] [2] [3] [4] GNAI1_HUMAN Guanine nucleotide-binding proteins (G proteins) are involved as modulators or transducers in various transmembrane signaling systems. The G(i) proteins are involved in hormonal regulation of adenylate cyclase: they inhibit the cyclase in response to beta-adrenergic stimuli. The inactive GDP-bound form prevents the association of RGS14 with centrosomes and is required for the translocation of RGS14 from the cytoplasm to the plasma membrane. May play a role in cell division.[5] [6]
References
- ↑ Li X, Staszewski L, Xu H, Durick K, Zoller M, Adler E. Human receptors for sweet and umami taste. Proc Natl Acad Sci U S A. 2002 Apr 2;99(7):4692-6. PMID:11917125 doi:10.1073/pnas.072090199
- ↑ Jang HJ, Kokrashvili Z, Theodorakis MJ, Carlson OD, Kim BJ, Zhou J, Kim HH, Xu X, Chan SL, Juhaszova M, Bernier M, Mosinger B, Margolskee RF, Egan JM. Gut-expressed gustducin and taste receptors regulate secretion of glucagon-like peptide-1. Proc Natl Acad Sci U S A. 2007 Sep 18;104(38):15069-74. PMID:17724330 doi:10.1073/pnas.0706890104
- ↑ Kim Y, Gumpper RH, Liu Y, Kocak DD, Xiong Y, Cao C, Deng Z, Krumm BE, Jain MK, Zhang S, Jin J, Roth BL. Bitter taste receptor activation by cholesterol and an intracellular tastant. Nature. 2024 Apr;628(8008):664-671. PMID:38600377 doi:10.1038/s41586-024-07253-y
- ↑ Hu X, Ao W, Gao M, Wu L, Pei Y, Liu S, Wu Y, Zhao F, Sun Q, Liu J, Jiang L, Wang X, Li Y, Tan Q, Cheng J, Yang F, Yang C, Sun J, Hua T, Liu ZJ. Bitter taste TAS2R14 activation by intracellular tastants and cholesterol. Nature. 2024 Jul;631(8020):459-466. PMID:38776963 doi:10.1038/s41586-024-07569-9
- ↑ Cho H, Kehrl JH. Localization of Gi alpha proteins in the centrosomes and at the midbody: implication for their role in cell division. J Cell Biol. 2007 Jul 16;178(2):245-55. PMID:17635935 doi:10.1083/jcb.200604114
- ↑ Johnston CA, Siderovski DP. Structural basis for nucleotide exchange on G alpha i subunits and receptor coupling specificity. Proc Natl Acad Sci U S A. 2007 Feb 6;104(6):2001-6. Epub 2007 Jan 30. PMID:17264214
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