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Viscarra, F.

Publications and source records attributed to Viscarra, F..

2 recordsLinked to original sources
bioRxiv2025

How Varenicline Works: Identifying Critical Receptor and Ligand-based Interactions

Approved by the FDA in 2006, varenicline became the first nicotinic-based therapeutic for smoking cessation and has since been used by tens of millions of smokers worldwide. Varenicline works by targeting the 4{beta}2 nicotinic acetylcholine receptor (nAChR), the primary focus for nicotine addiction, where ligand recognition by the receptor triggers ion channel opening. While widely recognized that vareniclines development was rooted in the well-established pharmacology of cytisine, the two compounds display notably different profiles, not only at nAChRs, but also at key off-target sites such as the 5-HT3 serotonin receptor. Despite vareniclines widespread use and proven efficacy as a smoking cessation aid, our knowledge of the precise molecular mechanism underlying its action, particularly the specific receptor-ligand interactions that underpin its functional specificity, remains incomplete. Through a multidisciplinary approach that integrates complementary fields of research, this study reveals the critical receptor-ligand interactions that distinguish varenicline from related nAChR agonists, such as cytisine and nicotine. Our findings reveal previously unrecognized, critical hydrogen bonding interactions within the 4{beta}2 binding sites, specifically involving 4T139, 4T183, and {beta}2S133, that are uniquely and selectively engaged by varenicline. Of these, {beta}2S133 emerged as the pivotal determinant of vareniclines function, with substitution by valine significantly impairing the ligand efficacy. Furthermore, the design and synthesis of novel varenicline analogues shed new light into the functional importance of the ligands quinoxaline moiety, revealing that not just the presence but also the precise positioning of this hydrogen bond acceptor are critical for receptor activation by varenicline. Together, these findings uncover a previously uncharacterized interaction network essential for vareniclines function at 4{beta}2, offering a deeper and more comprehensive framework for understanding its distinct pharmacological profile while expanding our broader understanding of how ligand binding is translated into function in these receptors. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=174 SRC="FIGDIR/small/659675v1_ufig1.gif" ALT="Figure 1"> View larger version (19K): org.highwire.dtl.DTLVardef@a77e39org.highwire.dtl.DTLVardef@4fec37org.highwire.dtl.DTLVardef@11d26a2org.highwire.dtl.DTLVardef@d35640_HPS_FORMAT_FIGEXP M_FIG C_FIG

pharmacology and toxicology↗
bioRxiv2025

Allosteric Control of Super-Agonism in a Ligand-Gated Ion Channel

Ligand-gated ion channels open in response to the binding of an agonist. The agonist binding site is typically located tens of Angstroms away from the channel gate, which lies within the membrane and thus the gating mechanism is considered a classic example of allostery within proteins. The multi-subunit nature of these proteins also means that modulatory effects on the gating process can also be mediated by several other distinct regions - so called allosteric modulatory sites. One of the most well-studied channels in this regard, is the nicotinic acetylcholine receptor. Super-agonists are compounds that can produce a greater maximal response than the endogenous ligand (acetylcholine in this case). They are able to stabilize the open state of the ion channel and this can have important consequences for neuronal signaling. Some super-agonist effects can be mediated through the orthosteric binding site, but others can be mediated by alternative binding sites. The latter are often much harder to identify and can depend very precisely on the subunit composition of the receptor. In this work we sought to identify the mechanism by which TC-2559, a known super-agonist that acts as such only at one particular combination of neuronal nicotinic acetylcholine receptors - the high sensitivity receptor which is comprised of 2 alpha subunits and 3 beta subunits (as opposed to the low sensitivity receptor which has 3 alpha and 2 beta subunits). By using advanced computational methods, supported by two-voltage electrode clamp experiments, we were able to show that TC-2559 not only binds to the orthosteric but also binds to the unique b2-b2 interface of the HS receptor. The binding of TC-2559 to this interface exerts unique interactions that other agonists are not able to make, but more importantly it induces changes in the interface that support that concept of an allosteric gain in overall efficacy. Our results highlight how allosteric control exists to modulate receptor function.

biochemistry↗