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Allosteric interactions between GB1 and GB2 subunits are required for optimal GABA(B) receptor function.

ABSTRACT: Recent studies on G-protein-coupled receptors revealed that they can dimerize. However, the role of each subunit in the activation process remains unclear. The gamma-amino-n-butyric acid type B (GABA(B)) receptor is comprised of two subunits: GB1 and GB2. Both consist of an extracellular domain (ECD) and a heptahelical domain composed of seven transmembrane alpha-helices, loops and the C-terminus (HD). Whereas GB1 ECD plays a critical role in ligand binding, GB2 is required not only to target GB1 subunit to the cell surface but also for receptor activation. Here, by analysing chimeric GB subunits, we show that only GB2 HD contains the determinants required for G-protein signalling. However, the HD of GB1 improves coupling efficacy. Conversely, although GB1 ECD is sufficient to bind GABA(B) ligands, the ECD of GB2 increases the agonist affinity on GB1, and is necessary for agonist activation of the receptor. These data indicate that multiple allosteric interactions between the two subunits are required for wild-type functioning of the GABA(B) receptor and highlight further the importance of the dimerization process in GPCR activation.

SUBMITTER: Galvez T

PROVIDER: S-EPMC125244 | biostudies-literature | 2001 May

REPOSITORIES: biostudies-literature

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Allosteric interactions between GB1 and GB2 subunits are required for optimal GABA(B) receptor function.

Galvez T T Duthey B B Kniazeff J J Blahos J J Blahos J J Rovelli G G Bettler B B Prézeau L L Pin J P JP

The EMBO journal 20010501 9

Recent studies on G-protein-coupled receptors revealed that they can dimerize. However, the role of each subunit in the activation process remains unclear. The gamma-amino-n-butyric acid type B (GABA(B)) receptor is comprised of two subunits: GB1 and GB2. Both consist of an extracellular domain (ECD) and a heptahelical domain composed of seven transmembrane alpha-helices, loops and the C-terminus (HD). Whereas GB1 ECD plays a critical role in ligand binding, GB2 is required not only to target GB ...[more]

PMID: 11331581

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Project description:Germination of Bacillus spores is triggered by the binding of specific nutrients to germinant receptors (GRs) located in the spore's inner membrane. The GRs typically consist of A, B, and C subunits, encoded by tricistronic ger operons. The Bacillus licheniformis genome contains the gerA family operons gerA, ynd, and gerK In contrast to the ABC(D) organization that characterizes gerA operons of many Bacillus species, B. licheniformis genomes contain a pentacistronic ynd operon comprising the yndD, yndE3 , yndE2 , yndF1 , and yndE1 genes encoding A, B, B, C, and B GR subunits, respectively (subscripts indicate paralogs). Here we show that B. licheniformis spores can germinate in the absence of the Ynd and GerK GRs, although cooperation between all three GRs is required for optimal germination with amino acids. Spores carrying an incomplete set of Ynd B subunits demonstrated reduced germination efficiencies, while depletion of all three Ynd B subunits restored germination of the spore population to levels only slightly lower than those of wild-type spores at high germinant concentrations. This suggests that the presence of an incomplete set of Ynd B subunits exhibits a dominant negative effect on germination and that the A and C subunits of the Ynd GR are sufficient for the cooperative functionality between Ynd and GerA. In contrast to the B subunits of Ynd, the B subunit of GerA was essential for amino acid-induced germination. This study provides novel insights into the role of individual GR subunits in the cooperative interaction between GRs in triggering spore germination.IMPORTANCE Spore-forming bacteria are problematic for the food industry, as spores can survive decontamination procedures and subsequently revive in food products, with the risk of food spoilage and foodborne disease. The Ynd and GerA germination receptors (GRs) cooperate in triggering efficient germination of Bacillus licheniformis spores when nutrients are present in the surrounding environment. This study shows that the single B subunit of GerA is essential for the cooperative function between Ynd and GerA, while the three B subunits of the Ynd GR are dispensable. The ability of GRs lacking individual subunits to stimulate germination together with other GRs could explain why ger operons lacking GR subunit genes are maintained in genomes of spore-forming species.

Dataset Information

Allosteric interactions between GB1 and GB2 subunits are required for optimal GABA(B) receptor function.

Publications

Allosteric interactions between GB1 and GB2 subunits are required for optimal GABA(B) receptor function.

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