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The serotonin transporter (SERT) terminates serotonin signaling and its activity is modulated by antidepressants. Here authors reveal the mechanistic details underlying the coupling between the two binding sites in SERT and a high-affinity ligand for the allosteric site.

The sigma 1 receptor (σ1R) is a unique endoplasmic reticulum membrane protein. Its ligands have been shown to possess therapeutic potential for neurological and substance use disorders among others. The E102Q mutation of σ1R has been found to elicit familial cases of amyotrophic lateral sclerosis (ALS). Despite reports of its downstream signaling consequences, the mechanistic details of the functional impact of E102Q at molecular level are not clear. Here, we investigate the molecular mechanism of the E102Q mutation with a spectrum of biochemical, biophysical, and pharmacological approaches. Our analysis of the interaction network of σ1R indicates that a set of residues near E102 is critical for the integrity of C-terminal ligand-binding domain. However, this integrity is not affected by the E102Q and E102A mutations, which is confirmed by the radioligand binding results. Instead, the E102 mutations disrupt the connection between the C-terminal domain and the N-terminal transmembrane helix (NT-helix). Results from bioluminescence resonance energy transfer and western blot assays demonstrate that these mutations destabilize higher-order σ1R oligomers, while our molecular dynamics simulations based on a σ1R crystal structure reveal a potential mechanism by which the mutations perturb the NT-helix dynamics. Thus, we propose that E102 is at a critical position in propagating the effects of ligand binding from the C-terminal domain to the NT-helix, while the latter may be involved in forming alternative oligomer interfaces, separate from the previously reported trimer interface. Together, these results provide the first account of the molecular mechanism of σ1R dysfunction caused by E102Q.

Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) are a powerful tool for neuroscience, but the standard DREADD ligand, CNO, has significant drawbacks. Here the authors report two novel high-potency DREADD ligands and a novel DREADD radiotracer for imaging purposes.

By analyzing and simulating inactive conformations of the highly homologous dopamine D2 and D3 receptors (D2R and D3R), we find that eticlopride binds D2R in a pose very similar to that in the D3R/eticlopride structure but incompatible with the D2R/risperidone structure. In addition, risperidone occupies a sub-pocket near the Na+ binding site, whereas eticlopride does not. Based on these findings and our experimental results, we propose that the divergent receptor conformations stabilized by Na+-sensitive eticlopride and Na+-insensitive risperidone correspond to different degrees of inverse agonism. Moreover, our simulations reveal that the extracellular loops are highly dynamic, with spontaneous transitions of extracellular loop 2 from the helical conformation in the D2R/risperidone structure to an extended conformation similar to that in the D3R/eticlopride structure. Our results reveal previously unappreciated diversity and dynamics in the inactive conformations of D2R. These findings are critical for rational drug discovery, as limiting a virtual screen to a single conformation will miss relevant ligands.

The dopamine D2 and D3 receptors (D2R and D3R) are important targets for antipsychotics and for the treatment of drug abuse. SB269652, a bitopic ligand that simultaneously binds both the orthosteric binding site (OBS) and a secondary binding pocket (SBP) in both D2R and D3R, was found to be a negative allosteric modulator. Previous studies identified Glu2.65 in the SBP to be a key determinant of both the affinity of SB269652 and the magnitude of its cooperativity with orthosteric ligands, as the E2.65A mutation decreased both of these parameters. However, the proposed hydrogen bond (H-bond) between Glu2.65 and the indole moiety of SB269652 is not a strong interaction, and a structure activity relationship study of SB269652 indicates that this H-bond may not be the only element that determines its allosteric properties. To understand the structural basis of the observed phenotype of E2.65A, we carried out molecular dynamics simulations with a cumulative length of ~77 μs of D2R and D3R wild-type and their E2.65A mutants bound to SB269652. In combination with Markov state model analysis and by characterizing the equilibria of ligand binding modes in different conditions, we found that in both D2R and D3R, whereas the tetrahydroisoquinoline moiety of SB269652 is stably bound in the OBS, the indole-2-carboxamide moiety is dynamic and only intermittently forms H-bonds with Glu2.65. Our results also indicate that the E2.65A mutation significantly affects the overall shape and size of the SBP, as well as the conformation of the N terminus. Thus, our findings suggest that the key role of Glu2.65 in mediating the allosteric properties of SB269652 extends beyond a direct interaction with SB269652, and provide structural insights for rational design of SB269652 derivatives that may retain its allosteric properties.

As genetic code expansion advances beyond L-α-amino acids to backbone modifications and new polymerization chemistries, delineating what substrates the ribosome can accommodate remains a challenge. The Escherichia coli ribosome tolerates non-L-α-amino acids in vitro, but few structural insights that explain how are available, and the boundary conditions for efficient bond formation are so far unknown. Here we determine a high-resolution cryogenic electron microscopy structure of the E. coli ribosome containing α-amino acid monomers and use metadynamics simulations to define energy surface minima and understand incorporation efficiencies. Reactive monomers across diverse structural classes favour a conformational space where the aminoacyl-tRNA nucleophile is

Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) are a popular chemogenetic technology for manipulation of neuronal activity in uninstrumented awake animals with potential for human applications as well. The prototypical DREADD agonist clozapine N-oxide (CNO) lacks brain entry and converts to clozapine, making it difficult to apply in basic and translational applications. Here we report the development of two novel DREADD agonists, JHU37152 and JHU37160, and the first dedicated 18F positron emission tomography (PET) DREADD radiotracer, [18F]JHU37107. We show that JHU37152 and JHU37160 exhibit high in vivo DREADD potency. [18F]JHU37107 combined with PET allows for DREADD detection in locally-targeted neurons, and at their long-range projections, enabling noninvasive and longitudinal neuronal projection mapping.

The Chimanimani Mountains of Mozambique and Zimbabwe harbour diverse and unique flora and fauna. Because of these unique floral characteristics, this region has received considerable attention by botanists. In contrast, the vertebrates occurring here have received little attention. The aim of this paper was to synthesise data collected on multiple recent surveys into the first annotated checklist of the mammals of the Mozambican side of the Chimanimani Mountains. We identified medium-sized and large mammals by exterior appearance, mostly as captured on camera traps. We combined morphological and molecular methods to identify small mammals, and we report on echolocation calls of some of the poorly known bat species. In total, we recorded 69 species, including 23 species of bats (Chiroptera), 15 species of rodents (Rodentia), 11 species of carnivores (Carnivora), nine species of ungulates (Cetartiodactyla), and the rest comprising Primates, Eulipotyphla, Lagomorpha, Proboscidea, and Pholidota. Of these, five species are listed as threatened, demonstrating the importance of the Chimanimani Mountains for mammalian biodiversity conservation in South Eastern Africa.

Abstract We recorded dopamine release signals in centromedial and centrolateral sectors of the striatum as mice learned consecutive versions of visual cue-outcome conditioning tasks. Dopamine release responses differed for the centromedial and centrolateral sites. In neither sector could these be accounted for by classic reinforcement learning alone as classically applied to the activity of nigral dopamine-containing neurons. Medially, cue responses ranged from initial sharp peaks to modulated plateau responses; outcome (reward) responses during cue conditioning were minimal or, initially, negative. At centrolateral sites, by contrast, strong, transient dopamine release responses occurred at both cue and outcome. Prolonged, plateau release responses to cues emerged in both regions when discriminative behavioral responses became required. At most sites, we found no evidence for a transition from outcome signaling to cue signaling, a hallmark of temporal difference reinforcement learning as applied to midbrain dopaminergic neuronal activity. These findings delineate a reshaping of striatal dopamine release activity during learning and suggest that current views of reward prediction error encoding need review to accommodate distinct learning-related spatial and temporal patterns of striatal dopamine release in the dorsal striatum.

Interoceptive exposure (IE) is a standard component of cognitive-behavioural therapy (CBT) for panic disorder and agoraphobia. The virtual reality (VR) program "Panic-Agoraphobia" has several virtual scenarios designed for applying exposure to agoraphobic situations; it can also simulate physical sensations. This work examines patients' acceptability of the IE component as applied in two different ways: using VR versus traditional IE. Additionally, it explores the relationship between users' treatment expectations and satisfaction and clinically significant change. Results showed that VR and traditional IE were well accepted by all participants. Furthermore, treatment expectations predicted efficacy.