Biology subjects

Krishna Kumar, K.

Publications and source records attributed to Krishna Kumar, K..

5 recordsLinked to original sources

bioRxiv2026

Discovery and dynamic pharmacology of μ-opioid receptor positive allosteric modulators

Opioid agonists such as morphine and fentanyl exert analgesic effects by binding and activating the {micro}-opioid receptor ({micro}OR), yet agonism of the {micro}OR causes a slate of serious side effects. {micro}OR-mediated addiction and respiratory depression are the major causes of the current opioid overdose crisis, largely driven by the explosion in illicit use of fentanyl, a potent opioid receptor full agonist. Given these serious side effects (and high resulting societal cost), molecules that act as analgesics with distinct mechanisms of action are of great interest. Positive allosteric modulators (PAMs) of the {micro}OR have the potential to avoid many off-target side effects of conventional opioid orthosteric agonists by enhancing the signaling properties of natural opioid peptide systems. We used a DNA-encoded chemical library screening approach to selectively discover active-state-specific {micro}OR PAMs. Two out of 3 selected prospective PAMs displayed the anticipated enhancement in agonist activity. The most effective of these compounds enhanced the activity of all orthosteric opioid agonists tested, including the native opioid peptide met-enkephalin. Little is known about the underlying dynamic basis of allosteric modulation of Family A GPCRs like the {micro}OR. To that end, we used single-molecule fluorescence resonance energy transfer experiments to detail the impact that our novel {micro}OR PAM has on the dynamic activation behavior of a key region on the intracellular face of the receptor. Our results here provide both a new chemical scaffold that acts as a {micro}OR PAM and detailed pharmacological and dynamic insights into its mechanism of action.

biophysics↗

bioRxiv2023

Negative allosteric modulation of the μ-opioid receptor

The {micro}-opioid receptor ({micro}OR) is a well-established target for analgesia, yet conventional opioid receptor agonists cause serious adverse effects, notably addiction and respiratory depression, which have led to the present opioid overdose epidemic. {micro}OR negative allosteric modulators (NAMs) may serve as powerful tools in preventing opioid overdose deaths, but promising chemical scaffolds remain elusive. We screened a large DNA-encoded chemical library against inactive {micro}OR, counter-screening with active, G-protein and agonist bound receptor to "steer" selections toward functional negative allosteric modulators. We discovered a NAM compound with high and selective enrichment to inactive {micro}OR; the molecule potently blocks the activity of orthosteric agonists and enhances the affinity of the key opioid overdose reversal molecule, naloxone. It accomplishes this by binding to a site on the extracellular vestibule proximal to naloxone, stabilizing a unique inactive conformation of the extracellular portions of the second and seventh transmembrane helices. The NAM perturbs orthosteric ligand kinetics in therapeutically desirable ways and works cooperatively with low doses of naloxone in vivo to inhibit morphine-induced antinociception, respiratory depression and conditioned place preference while minimizing withdrawal behaviors. Our results provide detailed structural insights into the mechanism of a negative allosteric modulator for the {micro}OR and demonstrate how it can be exploited in vivo.

biochemistry↗

bioRxiv2022

Negative allosteric modulation of the glucagon receptor by RAMP2

Receptor activity-modifying proteins (RAMPs) modulate the activity of many Family B heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors (GPCRs). The glucagon receptor (GCGR), a Family B GPCR responsible for maintenance of proper blood sugar levels, interacts with RAMP2, though the purpose and consequence of this interaction is poorly understood. Using a series of biochemical and cell-based assays, we show that RAMP2 interacts with and broadly inhibits GCGR-induced downstream signaling. Hydrogen-deuterium exchange monitored by mass spectrometry (HDX-MS) demonstrates that RAMP2 enhances local flexibility in select locations in and near the receptor extracellular domain (ECD) as well as at a key region in the 6th transmembrane helix, while single-molecule fluorescence resonance energy transfer (smFRET) experiments show that this RAMP2-induced ECD disorder results in inhibition of active and intermediate states of the intracellular face of the receptor. Using cryo-electron microscopy (cryoEM), we determined the structure of the GCGR-Gs complex at 2.9 [A] resolution in the presence of RAMP2. RAMP2 apparently does not interact with GCGR in an ordered manner, yet the ECD of GCGR is indeed largely disordered in the presence of RAMP2. This disorder is accompanied by rearrangements of several key areas of the receptor, resulting in the formation of a likely unproductive complex. Together, our studies suggest that RAMP2 acts as a negative allosteric modulator of GCGR by enhancing conformational sampling of the ECD.

biochemistry↗

bioRxiv2022

Modulation of cannabinoid receptor signaling by endocannabinoids

Endocannabinoids (eCBs) are endogenous lipid molecules that activate the cannabinoid receptor 1 (CB1), a G protein coupled receptor (GPCR) that signals primarily through the Gi/o family of G proteins to regulate neurotransmitter release. Consequently, CB1 is an important therapeutic target for several neurological disorders. How eCBs interact with CB1 is not known and the downstream signaling they activate is not well understood. In this study we show that eCBs do not activate Gi1 as much as synthetic cannabinoids. To characterize activation of CB1 by eCB, we formed an eCB analogue-bound (AMG315) CB1-Gi signaling complex for structural studies. The structure reveals differences in the orthosteric ligand binding pocket not seen in the previous CB1 structures, providing insights into the structural determinants of ligand efficacy. In combination with signaling and simulation data, this study provides mechanistic insights into CB1 activation by different classes of ligands, and sheds light on the G protein preferences between endogenous and exogenous ligands.

biochemistry↗

bioRxiv2019

Structural insights into ligand efficacy and activation of the glucagon receptor

The glucagon receptor family comprises Class B G protein-coupled receptors (GPCRs) that play a crucial role in regulating blood sugar levels. Receptors of this family represent important therapeutic targets for the treatment of diabetes and obesity. Despite intensive structural studies, we only have a poor understanding of the mechanism of peptide hormone-induced Class B receptor activation. This process involves the formation of a sharp kink in transmembrane helix 6 that moves out to allow formation of the nucleotide-free G protein complex. Here, we present the cryo-EM structure of the glucagon receptor (GCGR), a prototypical Class B GPCR, in complex with an engineered soluble glucagon derivative and the heterotrimeric G-protein, Gs. Comparison with the previously determined crystal structures of GCGR bound to a partial agonist reveals a structural framework to explain the molecular basis of ligand efficacy that is further supported by mutagenesis data.

biophysics↗