Biology subjects

Henin, J.

Publications and source records attributed to Henin, J..

7 recordsLinked to original sources

bioRxiv2025

Characterization of an Open-Channel Structure and Lateral Conduction Pathway in the Cation-Selective Pentameric Ligand-Gated Ion Channel, ELIC

Open-channel structures of multiple pentameric ligand-gated ion channels (pLGIC) have been determined, including the prokaryotic model pLGIC, ELIC (Erwinia ligand-gated ion channel). For many of these structures, it remains uncertain whether they represent the physiologic open-channel state because the conditions used for structure determination do not match those of functional measurements in cell membranes. Here, molecular dynamics (MD) simulation is used to examine the ion conduction properties of the ELIC open-channel structure, which was determined using a non-desensitizing mutant called ELIC5. Results from simulations show that the pore remains stably open on the microsecond timescale, but computational electrophysiology measurements demonstrate a large outward rectification, and an inward conductance that is significantly lower than experiment. This discrepancy is attributed to a constricted extracellular domain (ECD), which restricts the passage of ions between the ECD vestibule and extracellular solution. Unbiased MD simulation of the ELIC5 structure demonstrates spontaneous widening of an intersubunit space in the ECD to expose a lateral fenestration which becomes the dominant ion conduction pathway. Computational electrophysiology of the ELIC5 MD-refined structures with a widened lateral fenestration shows better agreement with experimental single-channel recordings. Mutations of residues along the lateral ion conduction pathway show reduced single-channel conductance, supporting the importance of the lateral fenestration for ion conduction in a cation-selective pLGIC.

biophysics↗

bioRxiv2025

Atomic scale description of the allosteric coupling between a lipid bilayer and a membrane protein

Biological membranes are complex environments whose functions are closely tied to the dynamic interactions between lipids and proteins. Here, we utilize high-pressure NMR of lipid nanodiscs paired with molecular dynamics simulations to elucidate at the atomic scale the allosteric dialog between the lipid bilayer and a bacterial model membrane protein, OmpX. We discover that OmpX delays the gelation process by liquefying the annular shell of lipids through hydrophobic and roughness matching processes at the protein surface. Furthermore, the alteration of the mechanical properties of the lipid bilayer directly impacts the energy landscape of amino acid side chains at the lipid/protein interface, but also, unexpectedly, at the protein core. Our work highlights a potential thermodynamically coupled but kinetically uncoupled allosteric pathway linking lipid dynamics with the interior of membrane proteins, directly impacting our understanding of membrane function. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=120 SRC="FIGDIR/small/634742v1_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@5c02ddorg.highwire.dtl.DTLVardef@c033c5org.highwire.dtl.DTLVardef@86f90forg.highwire.dtl.DTLVardef@149480e_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2022

Molecular determinants of inhibition of UCP1-mediated respiratory uncoupling

Brown adipose tissue expresses uncoupling protein 1 (UCP1), a mitochondrial transporter that uncouples respiration from ATP synthesis and dissipates energy as heat, making it a target for treating obesity and related metabolic disorders. Here, we combine molecular dynamics simulations with mitochondrial respiration assays to investigate how purine nucleotides inhibit respiration uncoupling by UCP1. Simulations predict that GDP binds UCP1 in the common substrate binding site in an upright orientation, where the base moiety interacts with a pair of charged residues (R92/E191) that are specifically conserved in the subfamily of UCPs. E191, among others, interacts with purine but not pyrimidine bases, suggesting a rationale for nucleotide specificity in UCP1 inhibition. We also identify a triplet of uncharged residues involved in hydrophobic contacts with GDP. Site-directed mutagenesis of either I187 or W281 to alanine increases lauric acid-induced uncoupling activity of UCP1 and partially suppresses inhibition of UCP1 activity by GDP in yeast spheroplasts. The triple mutant (F88, I187, W281) to alanine is overactivated by lauric acid even in a high concentration of purine nucleotides. Variants at these positions may help increase energy expenditure in a cellular and therapeutic context.

biophysics↗

bioRxiv2022

Computing absolute binding affinities by Streamlined Alchemical Free Energy Perturbation

Free Energy Perturbation (FEP) is a powerful but challenging computational technique for estimating differences in free energy between two or more states. This document is intended both as a tutorial and as an adaptable protocol for computing free energies of binding using free energy perturbations in NAMD. We present the Streamlined Alchemical Free Energy Perturbation (SAFEP) framework. SAFEP shifts the computational frame of reference from the ligand to the binding site itself. This both simplifies the thermodynamic cycle and makes the approach more broadly applicable to superficial sites and other less common geometries. As a practical example, we give instructions for calculating the absolute binding free energy of phenol to lysozyme. We assume familiarity with standard procedures for setting up, running, and analyzing molecular dynamics simulations using NAMD and VMD. While simulation times will vary, the human tasks should take no more than 3 to 4 hours for a reader without previous training in free energy calculations or experience with the VMD Colvars Dashboard. Sample data are provided for all key calculations both for comparison and readers convenience.

biophysics↗

bioRxiv2022

Structural mechanism of leaflet-specific phospholipid modulation of a pentameric ligand-gated ion channel

Pentameric ligand-gated ion channels (pLGICs) mediate synaptic transmission and are sensitive to their lipid environment. The mechanism of phospholipid modulation of any pLGIC is not well understood. We demonstrate that the model pLGIC, ELIC (Erwinia ligand-gated ion channel), is positively modulated by the anionic phospholipid, phosphatidylglycerol, from the outer leaflet of the membrane. To elucidate the mechanism of phosphatidylglycerol modulation, we determine a structure of ELIC in an open conformation. The structure shows a bound phospholipid in an outer leaflet site, and conformational changes in the phospholipid binding site unique to the open state. In combination with streamlined alchemical free energy perturbation calculations and functional measurements in asymmetric liposomes, the data support a mechanism by which an anionic phospholipid stabilizes the open state of a pLGIC by specific, state-dependent binding to this site.

biophysics↗

bioRxiv2021

A multiscale computational study of the conformation of the full-length intrinsically disordered protein MeCP2

The malfunction of the Methyl CpG binding protein 2 (MeCP2) is associated to the Rett syndrome, one of the most common causes of cognitive impairment in females. MeCP2 is an intrinsically disordered protein (IDP), making its experimental characterization a challenge. There is currently no structure available for the full-length MeCP2 in any of the databases, and only the structure of its MBD domain has been solved. We used this structure to build a full-length model of MeCP2 by completing the rest of the protein via ab initio modelling. Using a combination of all-atom and coarse-grained simulations, we characterized its structure and dynamics as well as the conformational space sampled by the ID and TRD domains in the absence of the rest of the protein. The present work is the first computational study of the full-length protein. Two main conformations were sampled in the coarse-grained simulations: a globular structure similar to the one observed in the all-atom force field and a two-globule conformation. Our all-atom model is in good agreement with the available experimental data, predicting amino acid W104 to be buried, amino acids R111 and R133 to be solvent accessible, and having 4.1% of -helix content, compared to the 4% found experimentally. Finally, we compared the model predicted by AlphaFold to our Modeller model. The model was not stable in water and underwent further folding. Together, these simulations provide a detailed (if perhaps incomplete) conformational ensemble of the full-length MeCP2, which is compatible with experimental data and can be the basis of further studies, e.g., on mutants of the protein or its interactions with its biological partners.

biochemistry↗

bioRxiv2019

Competitive dewetting underlies site-specific binding of general anesthetics to GABA(A) receptors

GABA(A) receptors are pentameric ligand-gated ion channels playing a critical role in the modulation of neuronal excitability. These inhibitory receptors, gated by{gamma} -aminobutyric acid (GABA), can be potentiated and even directly activated by intravenous and inhalational anesthetics. Intersubunit cavities in the transmembrane domain have been consistently identified as putative binding sites by numerous experiment and simulation results. Synaptic GABA(A) receptors are predominantly found in a 2:2{beta}:1{gamma} stoichiometry, with four unique inter-subunit interfaces. Experimental and computational results have suggested a perplexing specificity, given that cavity-lining residues are highly conserved, and the functional effects of general anesthetics are only weakly sensitive to most mutations of cavity residues. Here we use Molecular Dynamics simulations and thermodynamically rigorous alchemical free energy perturbation (AFEP) techniques to calculate affinities of the intravenous anesthetic propofol and the inhaled anesthetic sevoflurane to all intersubunit sites in a heteromeric GABA(A) receptor. We find that the best predictor of general anesthetic affinity for the intersubunit cavity sites is water displacement: combinations of anesthetic and binding site that displace more water molecules have higher affinities than those that displace fewer. The amount of water displacement is, in turn, a function of size of the general anesthetic, successful competition of the general anesthetic with water for the few hydrogen bonding partners in the site, and inaccessibility of the site to lipid acyl chains. The latter explains the surprisingly low affinity of GAs for the{gamma} - intersubunit site, which is missing a bulky methionine residue at the cavity entrance and can be occupied by acyl chains in the unbound state. Simulations also identify sevoflurane binding sites in the {beta} subunit centers and in the pore, but predict that these are lower affinity than the intersubunit sites.\n\nSignificanceAfter over a century of research, it is established that general anesthetics interact directly with hydrophobic cavities in proteins. We still do not know why not all small hydrophobic molecules can act as general anesthetics, or why not all hydrophobic cavities bind these molecules. General anesthetics can even select among homologous sites on one critical target, the GABA(A) heteropentamer, although the origins of selectivity are unknown. Here we used rigorous free energy calculations to find that binding affinity correlates with the number of released water molecules, which in turn depends upon the lipid content of the cavity without bound anesthetic. Results suggest a mechanism that reconciles lipid-centered and protein-centered theories, and which can directly inform design of new anesthetics.

biophysics↗