Biology subjects

Tasnim, A.

Publications and source records attributed to Tasnim, A..

5 recordsLinked to original sources

bioRxiv2026

Substrate-dependent oligomerization modulates DGAT1 activity and subcellular localization

Lipid Droplets (LDs) are ubiquitous organelles that are responsible for intracellular energy storage, in the form of highly esterified lipids such as triglycerides (TGs) and sterol esters. LDs emerge from and engage in stable contact sites with the endoplasmic reticulum (ER), where TG biosynthesis takes place by the action of the acyltransferase DGAT1. Despite the recent cryo-EM determination of the human dimeric structure of DGAT11,2, many aspects of the mechanism underlying TG synthesis in the ER remain unclear. Using a combination of molecular dynamics (MD) simulations, biochemical reconstitutions and fluorescence microscopy in live cells, we characterize several steps of DGAT1 molecular mechanism. We found that DAG preferentially enters the catalytic pocket of DGAT1 from the ER luminal leaflet, via a pathway that involves several conserved residues. Each DGAT1 subunit is able to bind multiple DAG molecules, and the presence of DAG promotes the formation of high-order DGAT1 oligomers. DGAT1 displays a preference for curved bilayers in silico, and it preferentially localizes in the ER tubular network, where LD formation is proposed to take place, upon the increase in its natural substrate diacylglycerol (DAG). Overall, our investigations provide a molecular view of how the interplay between protein oligomerization, subcellular localization and substrate biophysical properties modulate DGAT1 enzymatic activity.

cell biology↗

bioRxiv2025

Bioinformatics-based stereochemical elucidation of MM 46115: an unusual antiviral spirotetronate that inhibits clathrin-mediated endocytosis

The influenza virus is a leading cause of respiratory tract infection in humans, with the emergence of antiviral drug resistance posing an ongoing challenge to the treatment of influenza. This underscores the urgent need for effective new antiviral treatments. Spirotetronates are a family of bacterial natural products with a range of potent bioactivities. Some members of this family have antiviral activity. Here, we report the bioinformatics-based stereochemical assignment, antiviral properties, and mechanism of action of the unusual type II spirotetronate MM 46115 (renamed pellemicin). We show that pellemicin is active against both influenza A and B viruses at non-toxic concentrations, and inhibits clathrin-mediated endocytosis, which is required for virus internalisation. Given the need for new treatments for viral infections, the results of our work suggest that pellemicin and related spirotetronates could provide a basis for developing promising alternatives to existing antivirals to combat drug-resistant influenza. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=199 SRC="FIGDIR/small/677008v1_ufig1.gif" ALT="Figure 1"> View larger version (42K): org.highwire.dtl.DTLVardef@177aacforg.highwire.dtl.DTLVardef@16f0b26org.highwire.dtl.DTLVardef@144f9dcorg.highwire.dtl.DTLVardef@16fe673_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIMM 46115 (here renamed pellemicin) produced by a mycetoma pathogen is a promising antiviral C_LIO_LIThe pellemicin biosynthetic gene cluster was identified in Actinomadura pelletieri DSM 43383 C_LIO_LISequence analysis of biosynthetic enzymes enabled full stereochemical assignment C_LIO_LIPellemicin inhibits clathrin-mediated endocytosis, an early stage of the viral life cycle C_LI SignificanceThe influenza virus is a respiratory pathogen with epidemic and pandemic potential, resulting in tens of thousands of deaths each year and causing significant health, social and economic impact. The rise of resistant influenza strains against existing antiviral drugs creates a pressing need for alternative treatments. Natural products - specialised metabolites of bacteria, fungi, and plants that often have antimicrobial activity - are a promising source of therapeutics to treat human disease. Here, we identify a cryptic polyketide biosynthetic gene cluster in the genome sequence of Actinomadura pelletieri DSM 43383, an Actinomycete that causes mycetoma in humans. This is proposed to direct production of the previously reported spirotetronate MM 46115 (here renamed pellemicin), which has activity against the influenza virus. Sequence analyses of a polyketide synthase and Diels-Alderase involved in pellemicin biosynthesis, combined with comparative analysis of NMR data for other spirotetronates, enabled us to fully resolve longstanding stereochemical ambiguities in the structure of pellemicin. This underscores the emerging power of bioinformatics-based approaches, and their complementarity to traditional spectroscopic methods, for natural product structure elucidation. We also report extensive insights into the antiviral properties and mechanism of pellemicin, demonstrating that it exhibits antiviral activity at non-toxic doses for up to eight hours after administration and inhibits clathrin-mediated endocytosis, a process that many viruses exploit to enter cells. Only one other bacterial natural product, ikarugamycin, is known to inhibit clathrin-mediated endocytosis. Ikarugamycin contains a tetramate group, which bears a close structural relationship to the tetronate moiety of pellemicin, suggesting that inhibition of clathrin-mediated endocytosis may be a general mechanism of action for antiviral spirotetronates. Our findings therefore indicate that pellemicin, and related spirotetronate natural products, could form a basis for development of new drugs to combat antiviral resistance, and serve as useful tools to study the process of endocytosis.

microbiology↗

bioRxiv2023

Activity-dependent development of the body's touch receptors

We report a role for activity in the development of the primary sensory neurons that detect touch. Genetic deletion of Piezo2, the principal mechanosensitive ion channel in somatosensory neurons, caused profound changes in the formation of mechanosensory end organ structures and altered somatosensory neuron central targeting. Single cell RNA sequencing of Piezo2 conditional mutants revealed changes in gene expression in the sensory neurons activated by light mechanical forces, whereas other neuronal classes were less affected. To further test the role of activity in mechanosensory end organ development, we genetically deleted the voltage-gated sodium channel Nav1.6 (Scn8a) in somatosensory neurons throughout development and found that Scn8a mutants also have disrupted somatosensory neuron morphologies and altered electrophysiological responses to mechanical stimuli. Together, these findings indicate that mechanically evoked neuronal activity acts early in life to shape the maturation of the mechanosensory end organs that underlie our sense of gentle touch.

neuroscience↗

bioRxiv2023

The developmental timing of spinal touch processing alterations and its relation to ASD-associated behaviors in mouse models

Altered somatosensory reactivity is frequently observed among individuals with autism spectrum disorders (ASDs). Here, we report that while multiple mouse models of ASD exhibit aberrant somatosensory behaviors in adulthood, some models exhibit altered tactile reactivity as early as embryonic development, while in others, altered reactivity emerges later in life. Additionally, tactile over-reactivity during neonatal development is associated with anxiety-like behaviors and social interaction deficits in adulthood, whereas tactile over-reactivity that emerges later in life is not. The locus of circuit disruption dictates the timing of aberrant tactile behaviors: altered feedback or presynaptic inhibition of peripheral mechanosensory neurons leads to abnormal tactile reactivity during neonatal development, while disruptions in feedforward inhibition in the spinal cord lead to touch reactivity alterations that manifest later in life. Thus, the developmental timing of aberrant touch processing can predict the manifestation of ASD-associated behaviors in mouse models, and differential timing of sensory disturbance onset may contribute to phenotypic diversity across individuals with ASD.

neuroscience↗

bioRxiv2022

γ-Protocadherins control synapse formation and peripheral branching of touch sensory neurons

Light touch sensation begins with activation of low-threshold mechanoreceptor (LTMR) endings in the skin and propagation of their signals to the spinal cord and brainstem. We found that the clustered protocadherin gamma (Pcdhg) gene locus, which encodes 22 cell-surface homophilic binding proteins, is required in somatosensory neurons for normal behavioral reactivity to a range of tactile stimuli. Developmentally, distinct Pcdhg isoforms mediate LTMR synapse formation through neuron-neuron interactions and peripheral axonal branching through neuron-glia interactions. The Pcdhgc3 isoform mediates homophilic interactions between sensory axons and spinal cord neurons to promote synapse formation in vivo, and is sufficient to induce postsynaptic specializations in vitro. Moreover, loss of Pcdhgs and somatosensory synaptic inputs to the dorsal horn lead to fewer corticospinal synapses onto dorsal horn neurons. These findings reveal essential roles for Pcdhg isoform diversity in somatosensory neuron synapse formation, peripheral axonal branching, and step-wise assembly of central mechanosensory circuitry.

neuroscience↗