Biology subjects

Tieleman, D. P.

Publications and source records attributed to Tieleman, D. P..

17 recordsLinked to original sources

bioRxiv2026

Structural tuning of native type V fimbriae shapes mechanical specialization in Porphyromonas gingivalis

Fimbriae are proteinaceous filaments central to bacterial adhesion, colonization, and biofilm formation. Porphyromonas gingivalis, a keystone periodontal pathogen, utilizes two type V fimbriae systems, the major Fim and the minor Mfa fimbriae, that support distinct adhesive and biofilm-associated functions. Here, we determine the high-resolution cryo-electron microscopy structures of natively assembled FimA and Mfa1 stalks purified directly from P. gingivalis. Despite a shared donor-strand exchange mechanism, the two stalks exhibit distinct helical geometries and donor-strand environments. FimA has a larger helical pitch, whereas the Mfa1 donor strand is more extensively buried and further shielded by an ordered N-terminal latch. Comparison with monomeric stalk pilin structures reveals distinct assembly-associated remodeling around the donor-strand interface. Deletion of the Mfa1 latch reduces heat-resistant oligomer accumulation and produces species consistent with incomplete processing, yet recovered filaments retain the donor-strand-exchanged stalk architecture and exhibit initial force peaks comparable to native Mfa1 during simulated axial extension. Atomic force microscopy reveals greater apparent local stiffness of FimA under indentation, whereas steered molecular dynamics simulations show multiple lower-force axial transitions in FimA but a dominant higher-force transition in Mfa1. In both systems, the exchanged donor strands remain engaged during simulated extension while distinct surrounding contact networks rearrange. Together, these findings demonstrate how a conserved polymerization linkage can support structurally and mechanically distinct adhesive filaments, providing a molecular basis for mechanical diversification of type V fimbriae.

molecular biology↗

bioRxiv2026

Community Web Portal for Open Collaboration in the Martini Force Field Initiative

AO_SCPLOWBSTRACTC_SCPLOWThe Martini coarse-grained force field is widely used for biomolecular simulations by a large and rapidly expanding community worldwide. Over time, the development of Martini parameters, tools, and documentation has become increasingly dispersed across numerous research groups, leading to fragmentation and making it challenging for users and developers to keep track of the latest models, software, and best practices. Consequently, the development of Martini as a genuinely community-driven process has grown into a bottleneck. In response, the Martini Force Field Initiative (MFFI) has been established as an open-science effort to coordinate and support the collaborative development of all Martini resources. Here, we introduce the MFFI web portal, a platform designed around five core pillars: (i) avoiding reliance on a single group or local server; (ii) minimizing long-term maintenance overhead; (iii) reducing technical barriers for contributions; (iv) providing a unified home for parameters, tools, tutorials, example workflows, and research outputs; and (v) enabling timely dissemination of updates to the community. To achieve this, we use Quarto to generate a static website authored in Markdown, lowering the technical barrier to making contributions, and serverless architectures on Amazon Web Services for scalable, event-triggered backend operations. The source code is hosted in a public GitHub repository under an MIT license, with automated deployment via GitHub Actions and a contribution model based on pull requests for quality control. This design creates a sustainable, low-maintenance, and collaborative infrastructure that consolidates Martini resources and supports transparency. More broadly, our design exemplifies a transferable pattern for building open, community-oriented platforms for molecular modeling and computational science.

biophysics↗

bioRxiv2026

Cooperative Regulation of Membrane Domain Registration by Lipid Headgroup Size and Cholesterol Dynamics

The lateral organization of lipid domains and their coupling across the two leaflets are central to the structure of plasma membranes, yet the molecular determinants of domain registration and anti-registration remain incompletely understood. Here, we employ coarse-grained molecular dynamics simulations to investigate how lipid headgroup properties and cholesterol (CHOL) concentration regulate domain registration and anti-registration in symmetric model bilayers. Using a free energy perturbation (FEP)-like headgroup-interpolation approach to continuously interpolate between headgroup representations characteristic of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) lipids at a fixed tail composition, we show that headgroup properties and CHOL concentration act cooperatively through their effects on lipid packing and membrane curvature. Simulations with restrained CHOL flip-flop further demonstrate that transbilayer CHOL exchange actively strengthens interleaflet coupling and promotes domain registration. These results identify headgroup-dependent packing, CHOL-induced curvature, and CHOL flip-flop as cooperative determinants of domain organization in model membranes. TOC Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=114 SRC="FIGDIR/small/699701v2_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@1a78635org.highwire.dtl.DTLVardef@15c17f7org.highwire.dtl.DTLVardef@1295adaorg.highwire.dtl.DTLVardef@ba80a_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2024

Structural architecture of TolQ-TolR inner membrane protein complex from opportunistic pathogen Acinetobacter baumannii

Gram-negative bacteria harness the proton motive force (PMF) within their inner membrane (IM) to uphold the integrity of their cell envelope, an indispensable aspect for both division and survival. The IM TolQ-TolR complex is the essential part of the Tol-Pal system, serving as a conduit for PMF energy transfer to the outer membrane. Here we present cryo-EM reconstructions of Acinetobacter baumannii TolQ in apo and TolR- bound forms at atomic resolution. The apo TolQ configuration manifests as a symmetric pentameric pore, featuring a trans-membrane funnel leading towards a cytoplasmic chamber. In contrast, the TolQ-TolR complex assumes a proton non-permeable stance, characterized by the TolQ pentamers flexure to accommodate the TolR dimer, where two protomers undergo a translation-based relationship. Our structure-guided analysis and simulations support the rotor-stator mechanism of action, wherein the rotation of the TolQ pentamer harmonizes with the TolR protomers interplay. These findings broaden our mechanistic comprehension of molecular stator units empowering critical functions within the Gram-negative bacterial cell envelope. TeaserApo TolQ and TolQ-TolR structures depict structural rearrangements required for cell envelope organization in bacterial cell division.

molecular biology↗

bioRxiv2024

Endocannabinoid regulation of inward rectifier potassium (Kir) channels

The inward rectifier potassium channel Kir2.1 (KCNJ2) is an important regulator of resting membrane potential in both excitable and non-excitable cells. The functions of Kir2.1 channels are dependent on their lipid environment, including the availability of PI(4,5)P2, secondary anionic lipids, cholesterol and long-chain fatty acids acyl coenzyme A (LC-CoA). Endocannabinoids are a class of lipids that are naturally expressed in a variety of cells, including cardiac, neuronal, and immune cells. While these lipids are identified as ligands for cannabinoid receptors (CBRs), there is a growing body of evidence that they can directly regulate the function of numerous ion channels independently of CBRs. Here we examine the effects of a panel of endocannabinoids on Kir2.1 function and demonstrate that a subset of endocannabinoids can alter Kir2.1 conductance to varying degrees independently of CBRs. Using computational and SPR analysis, endocannabinoid regulation of Kir2.1 channels appears to be the result of altered membrane properties, rather than through direct protein-lipid interactions. Furthermore, differences in endocannabinoid effects on Kir4.1 and Kir7.1 channels, indicating that endocannabinoid regulation is not conserved among Kir family members. These findings may have broader implications on the function of cardiac, neuronal and/or immune cells.

biophysics↗

bioRxiv2023

Coarse-grained molecular dynamics simulations of lipid-protein interactions in SLC4 proteins

The SLC4 family of secondary bicarbonate transporters is responsible for the transport of HCO3-, CO32-, Cl-, Na+, K+, NH3 and H+ necessary for regulation of pH and ion homeostasis. They are widely expressed in numerous tissues throughout the body and function in different cell types with different membrane properties. Potential lipid roles in SLC4 function have been reported in experimental studies, focusing mostly on two members of the family: AE1 (Cl-/HCO3- exchanger) and NBCe1 (Na+-CO32- cotransporter). Previous computational studies of the outward facing (OF) state of AE1 with model lipid membranes revealed enhanced protein-lipid interactions between cholesterol (CHOL) and phosphatidylinositol bisphosphate (PIP2). However, the protein-lipid interactions in other members of the family and other conformation states are still poorly understood and this precludes the detailed studies of a potential regulatory role for lipids in the SLC4 family. In this work, we performed multiple 50 {micro}s coarse-grained molecular dynamics simulations on three members of the SLC4 family with different transport modes: AE1, NBCe1 and NDCBE (a Na+-CO32-/Cl- exchanger), in model HEK293 membranes consisting of CHOL, PIP2, phosphatidylcholine (POPC), phosphatidylethanolamine (POPE), phosphatidylserine (POPS), and sphingomyelin (POSM). The recently resolved inward-facing (IF) state of AE1 was also included in the simulations. Lipid-protein contact analysis of the simulated trajectories was performed with the ProLint server, which provides a multitude of visualization tools for illustration of areas of enhanced lipid-protein contact and identification of putative lipid binding sites within the protein matrix. We observed enrichment of CHOL and PIP2 around all proteins with subtle differences in their distribution depending on the protein type and conformation state. Putative binding sites were identified for CHOL, PIP2, POPC, and POSM in the three studied proteins and their potential roles in the SLC4 transport function, conformational transition and protein dimerization were discussed. Statement of significanceThe SLC4 protein family is involved in critical physiological processes like pH and blood pressure regulation and maintenance of ion homeostasis. Its members can be found in various tissues. A number of studies suggest possible lipid regulation of the SLC4 function. However, the protein-lipid interactions in the SLC4 family are still poorly understood. Here we make use of long coarse-grained molecular dynamics simulations to assess the protein-lipid interactions in three SLC4 proteins with different transport modes, AE1, NBCe1, and NDCBE. We identify putative lipid binding sites for several lipid types of potential mechanistic importance, discuss them in the framework of the known experimental data and provide a necessary basis for further studies on lipid regulation of SLC4 function.

biophysics↗

bioRxiv2022

Release of lipid nanodiscs from charged nano-droplets in the electrospray ionization process revealed by microsecond atomistic molecular dynamics simulations

Electrospray ionization (ESI) prevents the analyte being split into fragments and is widely used to analyze biomolecules. Nanodiscs provide a native-like environment for membrane proteins, while making them accessible in aqueous solution for analysis. We performed microsecond (s) molecular dynamics simulations at different temperatures, to provide atomistic insight in the release of intact nanodiscs from charged nano-droplets, the late stage of the ESI process. Two distinct main scenarios, at-center and off-center, were observed. The at-center scenario follows the charged residue model, and in the process the nanodisc stays well in the droplet interior, with the membrane scaffold protein (MSP) keeping its annular geometry. As solvent evaporates, lipids turn over to protect the hydrophilic surface. The off-center scenario conforms to a hybrid model of the charged residue model and chain ejection model. The nanodisc migrates to the water/air interface, leading to lipids escaping from the dissociated dimer and the partial ejection of one monomer of MSP. A diversity of morphologies of product gaseous ions was observed, as evidenced by their structural details, collision cross sections and moments of inertia. Our results are in reasonable agreement with results of mass spectrometry in mass-to-charge ratio, charge state and collision cross section. Our work displays the first atomistic view of a heterogeneous system, a lipid nanodisc, releasing from highly charged nano-droplets into the gas phase, which may provide structural supports for the interpretation of mass spectra of complicated systems. What we observe in our simulations could also be generalized to other protein-lipid systems.

biophysics↗

bioRxiv2021

The supramolecular organization of SARS-CoV and SARS-CoV-2 virions revealed by coarse-grained models of intact virus envelopes

The coronavirus disease 19 (COVID-19) pandemic is causing a global health crisis and has already caused a devastating societal and economic burden. The pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has a high sequence and architecture identity with SARS-CoV, but far more people have been infected by SARS-CoV-2. Here, combining structural data from cryo-EM and structure prediction, we constructed bottom-up Martini coarse-grained models of intact SARS-CoV and SARS-CoV-2 envelopes. Microsecond molecular dynamics simulations were performed, allowing us to explore their dynamics and supramolecular organization. Both SARS-CoV and SARS-CoV-2 envelopes present a spherical morphology with structural proteins forming multiple string-like islands in the membrane and clusters between heads of spike proteins. Critical differences between the SARS-CoV and SARS-CoV-2 envelopes are the interaction pattern between spike proteins and the flexibility of spike proteins. Our models provide structural and dynamic insights in the SARS virus envelopes, and could be used for further investigation, such as drug design, and fusion and fission processes.

biophysics↗

bioRxiv2021

Can two wrongs make a right? F508del-CFTR ion channel rescue by second-site mutations in its transmembrane domains

Deletion of phenylalanine 508 (F508del), in the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel, is the most common cause of cystic fibrosis (CF). F508 is located on nucleotide-binding domain 1 (NBD1) in contact with cytosolic extensions of transmembrane helices, in particular intracellular loop 4 (ICL4). We carried out a mutagenesis scan of ICL4 by introducing five or six second-site mutations at eleven positions in cis with F508del, and quantifying changes in membrane proximity and ion-channel function of CFTR. The scan strongly validated the effectiveness of R1070W at rescuing F508del defects. Molecular dynamics simulations highlighted two features characterizing the ICL4/NBD1 interface of F508del/R1070W-CFTR: flexibility, with frequent transient formation of interdomain hydrogen bonds, and loosely stacked aromatic sidechains, (F1068, R1070W, and F1074, mimicking F1068, F508 and F1074 in wild-type CFTR). F508del-CFTR had a distorted aromatic stack, with F1068 displaced towards space vacated by F508. In F508del/R1070F-CFTR, which largely retained F508del defects, R1070F could not form hydrogen bonds, and the interface was less flexible. Other ICL4 second-site mutations which partially rescued F508del-CFTR are F1068M and F1074M. Methionine side chains allow hydrophobic interactions without the steric rigidity of aromatic rings, possibly conferring flexibility to accommodate the absence of F508 and retain a dynamic interface. Finally, two mutations identified in a yeast scan (A141S and R1097T, on adjacent transmembrane helices linked to ICL1 and ICL4) also partially rescued F508del-CFTR function. These studies highlight the importance of hydrophobic interactions and conformational flexibility at the ICL4/NBD1 interface, advancing understanding of the structural underpinning of F508del dysfunction.

biophysics↗

bioRxiv2021

Structural characterization of the antimicrobial peptides myxinidin and WMR in bacterial membrane mimetic micelles and bicelles

Antimicrobial peptides are a promising class of alternative antibiotics that interact selectively with negatively charged lipid bilayers. This paper presents the structural characterization of the antimicrobial peptides myxinidin and WMR associated with bacterial membrane mimetic micelles and bicelles by NMR, CD spectroscopy, and Molecular Dynamics simulations. Both peptides adopt a different conformation in the lipidic environment than in aqueous solution. The location of peptides in micelles and bicelles has been studied by paramagnetic relaxation enhancement experiments with paramagnetic tagged 5- and 16-doxyl stearic acid (5-/16-SASL). Multi-microsecond long molecular dynamics simulations of multiple copies of the peptides were used to gain an atomic level of detail on membrane-peptide and peptide-peptide interactions. Our results highlight an essential role of the negatively charged membrane mimetic in the structural stability of both myxinidin and WMR. The peptides localize predominantly in the membranes headgroup region and have a noticeable membrane thinning effect on the overall bilayer structure. Myxinidin and WMR show different tendency to selfaggregate, which is also influenced by the membrane composition (DOPE/DOPG versus DOPE/DOPG/CL) and can be related to the previously observed difference in the ability of the peptides to disrupt different types of model membranes.

biochemistry↗

bioRxiv2021

Lipid distributions and transleaflet cholesterol migration near heterogeneous surfaces in asymmetric bilayers

Specific and nonspecific protein-lipid interactions in cell membranes have important roles in an abundance of biological functions. We have used coarse-grained (CG) molecular dynamics (MD) simulations to assess lipid distributions and cholesterol flipping dynamics around surfaces in a model asymmetric plasma membrane containing one of six structurally distinct entities: aquaporin-1 (AQP1), the bacterial {beta}-barrel outer membrane proteins OmpF and OmpX, KcsA potassium channel, WALP23 peptide, and a carbon nanotube (CNT). Our findings revealed varied lipid partitioning and cholesterol flipping times around the different solutes, and putative cholesterol binding sites in AQP1 and KcsA. The results suggest that protein-lipid interactions can be highly variable, and that surface-dependant lipid profiles are effectively manifested in CG simulations with the Martini force field.

biophysics↗

bioRxiv2020

Refinement of a Cryo-EM Structure of hERG: Bridging Structure and Function

The human ether-a-go-go-related gene (hERG) encodes the voltage gated potassium channel (KCNH2 or Kv11.1, commonly known as hERG). This channel plays a pivotal role in the stability of phase 3 repolarization of the cardiac action potential. Although a high-resolution cryo-EM structure is available for its depolarized (open) state, the structure surprisingly did not feature many functionally important interactions established by previous biochemical and electrophysiology experiments. Using Molecular Dynamics Flexible Fitting (MDFF), we refined the structure and recovered the missing functionally relevant salt bridges in hERG in its depolarized state. We also performed electrophysiology experiments to confirm the functional relevance of a novel salt bridge predicted by our refinement protocol. Our work shows how refinement of a high-resolution cryo-EM structure helps to bridge the existing gap between the structure and function in the voltage-sensing domain (VSD) of hERG. Statement of SignificanceCryo-EM has emerged as a major breakthrough technique in structural biology of membrane proteins. However, even high-resolution Cryo-EM structures contain poor side chain conformations and interatomic clashes. A high-resolution cryo-EM structure of hERG1 has been solved in the depolarized (open) state. The state captured by Cryo-EM surprisingly did not feature many functionally important interactions established by previous experiments. Molecular Dynamics Flexible Fitting (MDFF) used to enable refinement of the hERG1 channel structure in complex membrane environment re-establishing key functional interactions in the voltage sensing domain.

biophysics↗

bioRxiv2020

COX-1 - lipid interactions: arachidonic acid, cholesterol, and phospholipid binding to the membrane binding domain of COX-1

Cyclooxygenases carry out the committed step in prostaglandin synthesis and are the target of NSAIDs, the most widely used class of drugs in alleviating pain, fever, and inflammation. While extensively studied, one aspect of their biology that has been neglected is their interaction with membrane lipids. Such lipid-protein interactions have been shown to be a driving force behind membrane protein function and activity. Cyclooxygenases (COX-1 and COX-2) are bound on the luminal side of the endoplasmic reticulum membrane. The entrance to their active site is formed by a long hydrophobic channel which is used by the cyclooxygenase natural substrate, arachidonic acid, to access the enzyme. Using atomistic and coarse-grained simulations, we show that several membrane lipids are capable of accessing the same hydrophobic channel. We observe the preferential binding of arachidonic acid, cholesterol and glycerophospholipids with residues lining the cavity of the channel. We find that the membrane binding domain (MBD) of COX-1 is usually in a lipid-bound state and not empty. This orthosteric binding by other lipids suggests a potential regulatory role of membrane lipids with the possibility of affecting the COX-1 turnover rate. We also observed the unbiased binding of arachidonic acid to the MBD of COX-1 allowing us to clearly delineate its binding pathway. We identified a series of arginine residues as being responsible for guiding arachidonic acid towards the binding site. Finally, we were also able to identify the mechanism by which COX-1 induces a positive curvature on the membrane environment.

biophysics↗

bioRxiv2019

Membrane remodeling by the lytic fragment of sticholysin II: implications for the toroidal pore model

Sticholysins are pore-forming toxins of biomedical interest and represent a prototype of proteins acting through the formation of protein-lipid or toroidal pores. Peptides spanning the N-terminus of sticholysins can mimic their permeabilizing activity and together with the full-length toxins have been used as a tool to understand the mechanism of pore formation in membranes. However, the lytic mechanism of these peptides and the lipid shape modulating their activity are not completely clear. In this paper, we combine molecular dynamics (MD) simulations and experimental biophysical tools to dissect different aspects of the pore-forming mechanism of StII1-30, a peptide derived from the N-terminus of sticholysin II. With this combined approach, membrane curvature induction and flip-flop movement of the lipids were identified as two important membrane remodeling steps mediated by StII1-30-pore forming activity. Pore-formation by this peptide was enhanced by the presence of the negatively-curved lipid phosphatidylethanolamine (PE) in membranes. This lipid emerged not only as a facilitator of membrane interactions but also as a structural element of the StII1-30-pore that is recruited to the pore ring upon its assembly. Collectively, these new findings support a toroidal model for the architecture of the pore formed by this peptide and provide new molecular insight into the role of PE as a membrane component that easily accommodates into the ring of toroidal pores aiding in its stabilization. This study contributes to a better understanding of the molecular mechanism underlying the permeabilizing activity of StII1-30 and peptides or proteins acting via a toroidal pore mechanism and offers an informative framework for the optimization of the biomedical application of this and similar molecules.\n\nState of significanceWe provide evidence about the ability of StII1-30 to form toroidal pores. Due to pore assembly, StII1-30-pore induces membrane curvature and facilitates flip-flop movement of the lipids. The negatively-curved lipid PE relocates from the membrane into the pore ring, being also a structural element of the pore StII1-30 forms. This peptide emerged as a new tool, together with the full-length toxin, to understand the mechanism of toroidal pore formation in membranes. This study provides new molecular insight into the role of curved lipids as co-factors of toroidal pores, which could aid in its stabilization by easily accommodating into the ring. This framework could underpin strategies for the rational use of peptides or proteins acting via toroidal pores.

biophysics↗

bioRxiv2017

Structure of transmembrane helix 8 and possible membrane defects in CFTR

The cystic fibrosis transmembrane conductance regulator (CFTR) is an ion channel that regulates the flow of anions across epithelia. Mutations in CFTR cause cystic fibrosis. CFTR belongs to the ATP-Binding Cassette (ABC) transporter superfamily, and gating is controlled by phosphorylation and ATP binding and hydrolysis. Recent ATP-free and ATP-bound structures of zebrafish CFTR revealed an unwound segment of transmembrane helix (TM) 8, which appears to be a unique feature of CFTR not present in other ABC transporter structures. Here, by means of 1 s long molecular dynamics simulations, we investigate the interactions formed by this TM8 segment with nearby helices, in both ATP-free and ATP-bound states. We highlight the structural role of TM8 in maintaining the functional architecture of the pore and we describe a distinct membrane defect that is found near TM8 only in the ATP-free state. The results of the MD simulations are discussed in the context of the gating mechanism of CFTR.

biochemistry↗

bioRxiv2017

Lipid-Uptake Pathways and Lipid-Protein interactions in P-glycoprotein Revealed by Coarse-Grained Molecular Dynamics Simulations

P-glycoprotein (P-gp) exports a broad range of dissimilar compounds, including drugs, lipids and lipid-like molecules. Due to its substrate promiscuity, P-gp is a key player in the development of cancer multidrug resistance (MDR). Although P-gp is one of the most studied members of ABC-transporters, the mechanism of how its substrates access the cavity remains unclear. In this work, we performed coarse-grained (CG) molecular dynamics (MD) simulations to explore possible pathways of lipid-uptake in the inward-facing conformation of P-gp embedded in bilayers with different PC:PE lipid ratios. Our results show that in the inward facing orientation only lipids from the lower leaflet are taken up by the transporter. We identify positively charged residues at the portals of P-gp that favor lipid entrance to the cavity, as well as lipid binding sites, in good agreement with previous experimental studies. Our results show no selectivity for PC vs. PE lipids. We offer several examples of lipid uptake-pathways for PC and PE lipids that help to elucidate the molecular mechanism of substrate-uptake in P-gp.

biochemistry↗

bioRxiv2017

Lipid-protein interactions are unique fingerprints for membrane proteins

Cell membranes contain hundreds of different proteins and lipids in an asymmetric arrangement. Understanding the lateral organization principles of these complex mixtures is essential for life and health. However, our current understanding of the detailed organization of cell membranes remains rather elusive, owing to the lack of experimental methods suitable for studying these fluctuating nanoscale assemblies of lipids and proteins with the required spatiotemporal resolution. Here, we use molecular dynamics simulations to characterize the lipid environment of ten membrane proteins. To provide a realistic lipid environment, the proteins are embedded in a model plasma membrane, where more than 60 lipid species are represented, asymmetrically distributed between leaflets. The simulations detail how each protein modulates its local lipid environment through local lipid composition, thickness, curvature and lipid dynamics. Our results provide a molecular glimpse of the complexity of lipid-protein interactions, with potentially far reaching implications for the overall organization of the cell membrane.

biophysics↗