Biology subjects

Asher, W. B.

Publications and source records attributed to Asher, W. B..

5 recordsLinked to original sources

bioRxiv2026

CVN636 potentiates orthosteric agonist responses selectively at mGlu7/7 homodimers

The metabotropic glutamate receptor 7 (mGlu7) is an emerging therapeutic target for central nervous system disorders, but progress has been limited by a lack of selective pharmacological tools. CVN636 was recently reported as a potent and selective allosteric agonist of this receptor, capable of receptor activation in the absence of glutamate, with demonstrated efficacy in a rodent model of alcohol use disorder. Here, using complementary bioluminescence resonance energy transfer-based assays that measure both downstream signaling and G protein recruitment, we show that CVN636 does not activate the receptor on its own. Instead, CVN636 acts as a positive allosteric modulator that enhances the potency and efficacy of orthosteric agonist responses, including those of glutamate, in an agonist-dependent manner. Blockade of orthosteric agonist binding with a competitive antagonist abolished CVN636 activity, consistent with this mechanism. Furthermore, using an assay that distinguishes signaling from defined receptor dimers, we find that CVN636 activity is selective for mGlu7/7 homodimers and does not extend to any mGlu7-containing heterodimer tested. Thus, in our assay system CVN636 is an mGlu7/7 homodimer-selective positive allosteric modulator of this receptor, suggesting that its in vivo actions likely stem from action at these homomers.

pharmacology and toxicology↗

bioRxiv2026

Transmembrane Domain Dominance Drives Emergent Signaling and Allosteric Inversion in mGlu1/5 Heterodimers

Class C GPCRs function as obligate dimers in which only one G protein can engage the complex at a time, but how each protomer contributes to heterodimer coupling has remained unresolved. Using CODA-RET, a BRET-based assay reporting direct Gq recruitment to defined, full-length receptor pairs, we show that signaling at the mGlu/ heterodimer flows predominantly through the mGlu protomer; domain-swapped chimeras localize this dominance to the transmembrane domain. The dominance generates emergent signaling: cis-acting mGlu PAMs and NAMs undergo allosteric inversion when coupling is restricted to mGlu. By contrast, the mGlu-selective NAM MTEP is silent at the heterodimer, mirroring mGlus minimal role in driving Gq. Because the mGlu PAM tested acts only in cis, a trans-acting mGlu PAM would theoretically be selective for mGlu/ homomers. These findings open a pharmacological design space in which protomer target and cis-versus-trans mode of action tune selectivity across mGlu/, mGlu/, and mGlu/ dimers.

neuroscience↗

bioRxiv2026

Local GPCR density tips the balance of μ-opioid receptor trafficking

The extent to which local GPCR surface density governs engagement of downstream signaling and trafficking pathways remains unclear. Using single-particle tracking of the -opioid receptor (MOR), we show that receptor density differentially regulates G protein signaling and GRK2/3-{beta}-arrestin-dependent receptor trafficking. At low surface density, MORs activate G proteins but fail to enter clathrin-coated structures despite the presence of endogenous GRK2/3 and {beta}-arrestin. Increasing MOR density, co-expressing other class A GPCRs, or elevating GRK2 or {beta}-arrestin abundance rescues agonist-induced MOR trafficking. In contrast, the class B GPCR V2R blocks MOR trafficking at both low and high MOR densities. These results support a model in which increasing class A GPCR density, despite worsening effector-to-receptor stoichiometry, promotes trafficking by forming an affinity matrix that enables reversible GRK2/3 and {beta}-arrestin interactions to be productively used by neighboring receptors in a density-dependent manner, whereas class B GPCRs sequester {beta}-arrestin and block trafficking.

biophysics↗

bioRxiv2025

Conformational dynamics of the active state of β-arrestin 1

{beta}-arrestins ({beta}arr) regulate the signaling and trafficking of G protein-coupled receptors (GPCRs) in numerous physiological processes and have been implicated in various diseases. Structural and kinetic insights into how ligand-mediated GPCR activation drives {beta}arr coupling and activation remain limited, with the binding mechanism of the phosphorylated GPCR C-terminal tails, such as that of the vasopressin receptor-2 (V2Rpp), and the conformation of the entire {beta}arr tail in the active state still unknown. Here, we simulated both the basal and V2Rpp-bound states of {beta}arr1 with temperature replica-exchange molecular dynamics (TREMD) simulations to probe the activation mechanism of {beta}arr1. Compared to conventional MD, our TREMD simulations, employing an unprecedented 200-replica setup, significantly broadened conformational sampling while preserving the basal state. Our analysis showed that, without the bound Fab30 antibody fragment, the main body of V2Rpp-bound {beta}arr1 tended to transition toward the basal conformation; however, binding of V2Rpp in the N-domain groove allosterically oriented the finger loop to point upward for core engagement with a GPCR. Furthermore, V2Rpp dissociation events suggest that its binding involves a sliding movement along the N-domain groove, during which its phosphorylated residues p3 and p4 transiently occupy the S5 site to facilitate repositioning of p5 into the S5 site, thereby triggering a zippering process of p1 to p3. The dynamic 62-residue {beta}arr1 tail explored a vast conformational space, forming transient secondary structures, and could favorably anchor on the main bodys back side and within the central crest crevice. These findings elucidate key mechanistic steps underlying {beta}arr1 activation.

biophysics↗

bioRxiv2021

A novel mitragynine analog with low efficacy mu-opioid receptor agonism displays antinociception with attenuated adverse effects

Dried kratom leaves are anecdotally used for the treatment of pain, opioid dependence, and alcohol use disorder. We have previously shown that kratoms natural products (mitragynine) and semi-synthetic analogs (7-hydroxy mitragynine (7OH) and mitragynine pseudoindoxyl) are mu opioid receptor (MOR) agonists that show minimal {beta}-arrestin2 recruitment. To further investigate the structure activity relationships of G-protein potency, efficacy, and {beta}-arrestin2 recruitment, we diversified the mitragynine/7OH templates at the C9, -10 and -12 positions of the aromatic ring of the indole moiety. Three lead C9 analogs, synthesized by swapping the 9-methoxy group with varied substituents, namely phenyl (SC11), methyl (SC12), 3-furanyl (SC13), were further characterized using a panel of in vitro and ex vivo electrophysiology assays. All three compounds were partial agonists with lower efficacy than both DAMGO and morphine in heterologous G-protein assays and synaptic physiology. SC11-13 also showed lower recruitment of both {beta}-arrestin subtypes compared to DAMGO, and in assays with limited MOR receptor reserve, the G-protein efficacy of SC11, SC12 and SC13 was comparable to buprenorphine. In mouse models, at equianalgesic doses SC13 showed MOR-dependent analgesia with potency similar to morphine without respiratory depression, hyperlocomotion, constipation, or place conditioning. Taken together, these results suggest that MOR agonists with a G-protein efficacy profile similar to buprenorphine can be developed into opioids that are effective analgesics with greatly reduced liabilities.

pharmacology and toxicology↗