Biology subjects

Tan, B. K.

Publications and source records attributed to Tan, B. K..

4 recordsLinked to original sources

bioRxiv2026

Dynamics of dopamine transients in human olfactory epithelium during reward learning

Dopamine signaling is crucial for motivation, movement, and learning, but has remained beyond the reach of measurement in healthy humans. Here, we measured sub-second dopamine in the olfactory epithelium of healthy humans during two reward learning tasks with distinct reward types: liquid reward during a conditioning task and monetary reward during an economic exchange game. In both tasks, as trials progress, peak dopamine transients shift from rewarding outcomes back to reward-predictive cues. In the economic game, this pattern retrains quickly when reward magnitude or reward timing is changed without warning. These findings match the time transfer characteristics and amplitude dependence of temporal difference prediction error signals. The results also establish a new, minimally invasive route for recording fast dopamine signaling in healthy humans: the nose.

neuroscience↗

bioRxiv2025

Structural mechanism of lipid modulation of pentameric ligand-gated ion channel activity

Pentameric ligand-gated ion channels (pLGICs) are sensitive to the lipid environment. However, the structural mechanism of how specific lipids support the agonist response of any pLGIC is poorly understood. Using the model pLGIC, ELIC (Erwinia ligand-gated ion channel), we find that phosphatidylethanolamine (PE) or cardiolipin (CL) are sufficient to support activation of a non-desensitizing mutant called ELIC5. Cryo-EM structures of unliganded and agonist-bound ELIC5 in the absence of PE or CL show increased structural heterogeneity and destabilization of the resting and open-channel states. Importantly, the unliganded structure of ELIC5 in a phosphatidylcholine (PC)-only environment shows variability that resembles agonist-induced changes. The structures also reveal a CL binding site at an outer leaflet M3-M4 site. Together with functional measurements in asymmetric liposomes and coarse-grained molecular dynamics simulations, the data indicate that CL supports ELIC activity by binding to this M3-M4 site thereby stabilizing an agonist-responsive resting state of the channel.

biophysics↗

bioRxiv2025

Cryo-EM structures of a pentameric ligand-gated ion channel in liposomes

Detergents and lipid nanodiscs affect the cryo-EM structures of pentameric ligand-gated ion channels (pLGICs) including ELIC. To determine the structure of a pLGIC in a membrane environment that supports ion channel function, we performed single particle cryo-EM of ELIC in liposomes. ELIC activation and desensitization were confirmed in liposomes with a stopped-flow thallium flux assay. Using WT ELIC and a non-desensitizing mutant (ELIC5), we captured resting, activated and desensitized structures at high resolution. In the desensitized structure, the ion conduction pore has a constriction at the 9 leucine of the pore-lining M2 helix, indicating that 9 is the desensitization gate in ELIC. The agonist-bound structures of ELIC in liposomes are distinct from those in nanodiscs. In general, the transmembrane domain is more loosely packed in liposomes compared to nanodiscs. It has been suggested that large nanodiscs are superior for supporting membrane protein function. However, ELIC localizes to the rim of large circularized nanodiscs, and structures of ELIC in large nanodiscs deviate from the liposome structures more than those in small nanodiscs. Using liposomes for cryo-EM structure determination of a pLGIC increases our confidence that the structures are snapshots of functional states.

biophysics↗

bioRxiv2019

Multi-omics co-localization with genome-wide association studies reveals context-specific mechanisms of asthma risk variants

BackgroundGenome-wide association studies (GWASs) have identified thousands of variants associated with asthma and other complex diseases. However, the functional effects of most of these variants are unknown. Moreover, GWASs do not provide context-specific information on cell types or environmental factors that affect specific disease risks and outcomes. To address these limitations, we used an upper airway (sinonasal) epithelial cell culture model to assess transcriptional and epigenetic responses to an asthma-promoting pathogen, rhinovirus (RV), and provide context-specific functional annotations to variants discovered in GWASs of asthma. MethodsUsing genome-wide genetic, gene expression and DNA methylation data in vehicle- and RV-treated airway epithelial cells (AECs) from 104 individuals, we mapped cis expression and methylation quantitative trait loci (cis-eQTLs and cis-meQTLs, respectively) in each condition. A Bayesian test for co-localization between AEC molecular QTLs and adult onset and childhood onset GWAS variants was used to assign function to variants associated with asthma. Mendelian randomization was applied to demonstrate DNA methylation effects on gene expression at asthma colocalized loci. ResultsCo-localization analyses of airway epithelial cell molecular QTLs with asthma GWAS variants revealed potential molecular disease mechanisms of asthma, including QTLs at the TSLP locus that were common to both exposure conditions and to both childhood and adult onset asthma, as well as QTLs at the 17q12-21 asthma locus that were specific to RV exposure and childhood onset asthma, consistent with clinical and epidemiological studies of these loci. ConclusionThis study provides information on functional effects of asthma risk variants in airway epithelial cells and insight into a disease-relevant viral exposure that modulates genetic effects on transcriptional and epigenetic responses in cells and on risk for asthma in GWASs.

genetics↗