Lipochitin oligosaccharides called Nod factors function as primary rhizobial signal molecules triggering legumes to develop new plant organs: root nodules that host the bacteria as nitrogen-fixing bacteroids. Here, we show that the Lotus japonicus Nod factor receptor 5 (NFR5) and Nod factor receptor 1 (NFR1) bind Nod factor directly at high-affinity binding sites. Both receptor proteins were posttranslationally processed when expressed as fusion proteins and extracted from purified membrane fractions of Nicotiana benthamiana or Arabidopsis thaliana . The N-terminal signal peptides were cleaved, and NFR1 protein retained its in vitro kinase activity. Processing of NFR5 protein was characterized by determining the N -glycosylation patterns of the ectodomain. Two different glycan structures with identical composition, Man ₃ XylFucGlcNAc ₄ , were identified by mass spectrometry and located at amino acid positions N68 and N198. Receptor–ligand interaction was measured by using ligands that were labeled or immobilized by application of chemoselective chemistry at the anomeric center. High-affinity ligand binding was demonstrated with both solid-phase and free solution techniques. The K _d values obtained for Nod factor binding were in the nanomolar range and comparable to the concentration range sufficient for biological activity. Structure-dependent ligand specificity was shown by using chitin oligosaccharides. Taken together, our results suggest that ligand recognition through direct ligand binding is a key step in the receptor-mediated activation mechanism leading to root nodule development in legumes.

Plants associate with beneficial arbuscular mycorrhizal fungi facilitating nutrient acquisition. Arbuscular mycorrhizal fungi produce chitooligosaccharides (COs) and lipo-chitooligosaccharides (LCOs), that promote symbiosis signalling with resultant oscillations in nuclear-associated calcium. The activation of symbiosis signalling must be balanced with activation of immunity signalling, which in fungal interactions is promoted by COs resulting from the chitinaceous fungal cell wall. Here we demonstrate that COs ranging from CO4-CO8 can induce symbiosis signalling in Medicago truncatula. CO perception is a function of the receptor-like kinases MtCERK1 and LYR4, that activate both immunity and symbiosis signalling. A combination of LCOs and COs act synergistically to enhance symbiosis signalling and suppress immunity signalling and receptors involved in both CO and LCO perception are necessary for mycorrhizal establishment. We conclude that LCOs, when present in a mix with COs, drive a symbiotic outcome and this mix of signals is essential for arbuscular mycorrhizal establishment.

The in vitro and in vivo pharmacological properties of N-(4-fluorophenylmethyl)-N-(1-methylpiperidin-4-yl)-N′-(4-(2-methylpropyloxy)phenylmethyl)carbamide (2R,3R)-dihydroxybutanedioate (2:1) (ACP-103) are presented. A potent 5-hydroxytryptamine (5-HT)_2A receptor inverse agonist ACP-103 competitively antagonized the binding of [³H]ketanserin to heterologously expressed human 5-HT_2A receptors with a mean pK_i of 9.3 in membranes and 9.70 in whole cells. ACP-103 displayed potent inverse agonist activity in the cell-based functional assay receptor selection and amplification technology (R-SAT), with a mean pIC₅₀ of 8.7. ACP-103 demonstrated lesser affinity (mean pK_i of 8.80 in membranes and 8.00 in whole cells, as determined by radioligand binding) and potency as an inverse agonist (mean pIC₅₀ 7.1 in R-SAT) at human 5-HT_2C receptors, and lacked affinity and functional activity at 5-HT_2B receptors, dopamine D₂ receptors, and other human monoaminergic receptors. Behaviorally, ACP-103 attenuated head-twitch behavior (3 mg/kg p.o.), and prepulse inhibition deficits (1-10 mg/kg s.c.) induced by the 5-HT_2A receptor agonist (±)-2,5-dimethoxy-4-iodoamphetamine hydrochloride in rats and reduced the hyperactivity induced in mice by the N-methyl-d-aspartate receptor noncompetitive antagonist 5H-dibenzo[a,d]cyclohepten-5,10-imine (dizocilpine maleate; MK-801) (0.1 and 0.3 mg/kg s.c.; 3 mg/kg p.o.), consistent with a 5-HT_2A receptor mechanism of action in vivo and antipsychotic-like efficacy. ACP-103 demonstrated >42.6% oral bioavailability in rats. Thus, ACP-103 is a potent, efficacious, orally active 5-HT_2A receptor inverse agonist with a behavioral pharmacological profile consistent with utility as an antipsychotic agent.

Switching perception of friend and foe: Lysine motif receptors in plants perceive glycans that signal the presence of pathogenic or symbiotic nitrogen-fixing microbes. Bozsoki et al. now define the portions of these receptors that create the discriminatory binding pocket (see the Perspective by Bisseling and Geurts). The motifs were conserved in receptors that initiate immune responses, reflecting the invariable nature of the chitin fragments that they sense. Conversely, the motifs in receptors that respond to symbiotic signals were more varied, reflecting the greater diversity of the lipochitooligosaccharides (Nod factors) that they sense. With domain swapping, the authors switched the Nod factor specificity of receptors from two legume species and also enabled a chitin receptor that was otherwise dedicated to the detection of pathogenic microbes to instead recognize Nod factors. Science , this issue p. 663 ; see also p. 620