Selinger, T. L. | Search bioRxiv

bioRxiv2025

Deciphering Ibogaines Matrix Pharmacology: Multiple Transporter Modulation at Serotonin Synapses

Ibogaine is the main psychoactive alkaloid produced by the iboga tree (Tabernanthe iboga) that has a unique therapeutic potential across multiple indications, including opioid dependence, substance use disorders, depression, anxiety, posttraumatic stress disorder (PTSD), and traumatic brain injury (TBI). We systematically examined the effects of ibogaine, its main metabolite noribogaine, and a series of iboga analogs at monoamine neurotransmitter transporters, some which have been linked to the oneiric and therapeutic effects of these substances. We report that ibogaine and noribogaine inhibit the transport function of the vesicular monoamine transporter 2 (VMAT2) with sub-micromolar potency in cell-based fluorimetry assays and at individual synaptic vesicle clusters in mouse brain as demonstrated via two-photon microscopy. The iboga compounds also inhibit the plasma membrane monoamine transporters (MATs), prominently including the serotonin transporter (SERT), and a novel iboga target, the organic cation transporter 2 (OCT2). SERT transport inhibition was demonstrated in serotonin axons and soma in the brain and in rat brain synaptosomes, where ibogaine and its analogs did not act as substrate-type serotonin releasers. Noribogaine showed dual inhibition of VMAT2 and SERT with comparable potency, providing an explanatory model for the known neurochemical effects of ibogaine in rodents. Together, the updated profile of the monoamine transporter modulation offers insight into the complexity of the iboga pharmacology, which we termed "matrix pharmacology". The matrix pharmacology concept is outlined and used to explain why ibogaine and noribogaine do not induce catalepsy, as demonstrated in our study, in contrast to other VMAT2 inhibitors. TOC Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/641351v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@a1cacaorg.highwire.dtl.DTLVardef@8be27org.highwire.dtl.DTLVardef@1fc320forg.highwire.dtl.DTLVardef@3a8837_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2023

Sm-like protein Rof inhibits transcription termination factor Rho by binding site obstruction and conformational insulation

Transcription termination factor {rho} is a hexameric, RNA-dependent NTPase that can adopt active closed-ring and inactive open-ring conformations. The Sm-like protein Rof, a homolog of the RNA chaperone Hfq, inhibits {rho}-dependent termination in vivo but recapitulation of this activity in vitro has proven difficult and the precise mode of Rof action is presently unknown. Our electron microscopic structures of {rho}-Rof and {rho}-RNA complexes show that Rof undergoes pronounced conformational changes to bind {rho} at the protomer interfaces, undercutting {rho} conformational dynamics associated with ring closure and occluding extended primary RNA-binding sites that are also part of interfaces between {rho} and RNA polymerase. Consistently, Rof impedes {rho} ring closure, {rho}-RNA interactions, and {rho} association with transcription elongation complexes. Structure-guided mutagenesis coupled with functional assays confirmed that the observed {rho}-Rof interface is required for Rof-mediated inhibition of cell growth and {rho}-termination in vitro. Bioinformatic analyses revealed that Rof is restricted to Pseudomonadota and that the {rho}-Rof interface is conserved. Genomic contexts of rof differ between Enterobacteriaceae and Vibrionaceae, suggesting distinct modes of Rof regulation. We hypothesize that Rof and other cellular anti-terminators silence {rho} under diverse, but yet to be identified, stress conditions when unrestrained transcription termination by {rho} would be lethal.

biochemistry↗