@article{14782, abstract = {The actin cortex is a complex cytoskeletal machinery that drives and responds to changes in cell shape. It must generate or adapt to plasma membrane curvature to facilitate diverse functions such as cell division, migration, and phagocytosis. Due to the complex molecular makeup of the actin cortex, it remains unclear whether actin networks are inherently able to sense and generate membrane curvature, or whether they rely on their diverse binding partners to accomplish this. Here, we show that curvature sensing is an inherent capability of branched actin networks nucleated by Arp2/3 and VCA. We develop a robust method to encapsulate actin inside giant unilamellar vesicles (GUVs) and assemble an actin cortex at the inner surface of the GUV membrane. We show that actin forms a uniform and thin cortical layer when present at high concentration and distinct patches associated with negative membrane curvature at low concentration. Serendipitously, we find that the GUV production method also produces dumbbell-shaped GUVs, which we explain using mathematical modeling in terms of membrane hemifusion of nested GUVs. We find that branched actin networks preferentially assemble at the neck of the dumbbells, which possess a micrometer-range convex curvature comparable with the curvature of the actin patches found in spherical GUVs. Minimal branched actin networks can thus sense membrane curvature, which may help mammalian cells to robustly recruit actin to curved membranes to facilitate diverse cellular functions such as cytokinesis and migration.}, author = {Baldauf, Lucia and Frey, Felix F and Arribas Perez, Marcos and Idema, Timon and Koenderink, Gijsje H.}, issn = {0006-3495}, journal = {Biophysical Journal}, keywords = {Biophysics}, number = {11}, pages = {2311--2324}, publisher = {Elsevier}, title = {{Branched actin cortices reconstituted in vesicles sense membrane curvature}}, doi = {10.1016/j.bpj.2023.02.018}, volume = {122}, year = {2023}, } @article{14844, abstract = {Many cell functions require a concerted effort from multiple membrane proteins, for example, for signaling, cell division, and endocytosis. One contribution to their successful self-organization stems from the membrane deformations that these proteins induce. While the pairwise interaction potential of two membrane-deforming spheres has recently been measured, membrane-deformation-induced interactions have been predicted to be nonadditive, and hence their collective behavior cannot be deduced from this measurement. We here employ a colloidal model system consisting of adhesive spheres and giant unilamellar vesicles to test these predictions by measuring the interaction potential of the simplest case of three membrane-deforming, spherical particles. We quantify their interactions and arrangements and, for the first time, experimentally confirm and quantify the nonadditive nature of membrane-deformation-induced interactions. We furthermore conclude that there exist two favorable configurations on the membrane: (1) a linear and (2) a triangular arrangement of the three spheres. Using Monte Carlo simulations, we corroborate the experimentally observed energy minima and identify a lowering of the membrane deformation as the cause for the observed configurations. The high symmetry of the preferred arrangements for three particles suggests that arrangements of many membrane-deforming objects might follow simple rules.}, author = {Azadbakht, Ali and Meadowcroft, Billie and Majek, Juraj and Šarić, Anđela and Kraft, Daniela J.}, issn = {1542-0086}, journal = {Biophysical Journal}, publisher = {Elsevier}, title = {{Nonadditivity in interactions between three membrane-wrapped colloidal spheres}}, doi = {10.1016/j.bpj.2023.12.020}, year = {2023}, } @article{10530, abstract = {Cell dispersion from a confined area is fundamental in a number of biological processes, including cancer metastasis. To date, a quantitative understanding of the interplay of single cell motility, cell proliferation, and intercellular contacts remains elusive. In particular, the role of E- and N-Cadherin junctions, central components of intercellular contacts, is still controversial. Combining theoretical modeling with in vitro observations, we investigate the collective spreading behavior of colonies of human cancer cells (T24). The spreading of these colonies is driven by stochastic single-cell migration with frequent transient cell-cell contacts. We find that inhibition of E- and N-Cadherin junctions decreases colony spreading and average spreading velocities, without affecting the strength of correlations in spreading velocities of neighboring cells. Based on a biophysical simulation model for cell migration, we show that the behavioral changes upon disruption of these junctions can be explained by reduced repulsive excluded volume interactions between cells. This suggests that in cancer cell migration, cadherin-based intercellular contacts sharpen cell boundaries leading to repulsive rather than cohesive interactions between cells, thereby promoting efficient cell spreading during collective migration. }, author = {Zisis, Themistoklis and Brückner, David and Brandstätter, Tom and Siow, Wei Xiong and d’Alessandro, Joseph and Vollmar, Angelika M. and Broedersz, Chase P. and Zahler, Stefan}, issn = {0006-3495}, journal = {Biophysical Journal}, keywords = {Biophysics}, number = {1}, pages = {P44--60}, publisher = {Elsevier}, title = {{Disentangling cadherin-mediated cell-cell interactions in collective cancer cell migration}}, doi = {10.1016/j.bpj.2021.12.006}, volume = {121}, year = {2022}, } @article{10340, abstract = {The cell membrane is an inhomogeneous system composed of phospholipids, sterols, carbohydrates, and proteins that can be directly attached to underlying cytoskeleton. The protein linkers between the membrane and the cytoskeleton are believed to have a profound effect on the mechanical properties of the cell membrane and its ability to reshape. Here, we investigate the role of membrane-cortex linkers on the extrusion of membrane tubes using computer simulations and experiments. In simulations, we find that the force for tube extrusion has a nonlinear dependence on the density of membrane-cortex attachments: at a range of low and intermediate linker densities, the force is not significantly influenced by the presence of the membrane-cortex attachments and resembles that of the bare membrane. For large concentrations of linkers, however, the force substantially increases compared with the bare membrane. In both cases, the linkers provided membrane tubes with increased stability against coalescence. We then pulled tubes from HEK cells using optical tweezers for varying expression levels of the membrane-cortex attachment protein Ezrin. In line with simulations, we observed that overexpression of Ezrin led to an increased extrusion force, while Ezrin depletion had a negligible effect on the force. Our results shed light on the importance of local protein rearrangements for membrane reshaping at nanoscopic scales.}, author = {Paraschiv, Alexandru and Lagny, Thibaut J. and Campos, Christian Vanhille and Coudrier, Evelyne and Bassereau, Patricia and Šarić, Anđela}, issn = {0006-3495}, journal = {Biophysical Journal}, keywords = {biophysics}, number = {4}, pages = {598--606}, publisher = {Cell Press}, title = {{Influence of membrane-cortex linkers on the extrusion of membrane tubes}}, doi = {10.1016/j.bpj.2020.12.028}, volume = {120}, year = {2021}, } @article{10338, abstract = {In the nuclear pore complex, intrinsically disordered proteins (FG Nups), along with their interactions with more globular proteins called nuclear transport receptors (NTRs), are vital to the selectivity of transport into and out of the cell nucleus. Although such interactions can be modeled at different levels of coarse graining, in vitro experimental data have been quantitatively described by minimal models that describe FG Nups as cohesive homogeneous polymers and NTRs as uniformly cohesive spheres, in which the heterogeneous effects have been smeared out. By definition, these minimal models do not account for the explicit heterogeneities in FG Nup sequences, essentially a string of cohesive and noncohesive polymer units, and at the NTR surface. Here, we develop computational and analytical models that do take into account such heterogeneity in a minimal fashion and compare them with experimental data on single-molecule interactions between FG Nups and NTRs. Overall, we find that the heterogeneous nature of FG Nups and NTRs does play a role in determining equilibrium binding properties but is of much greater significance when it comes to unbinding and binding kinetics. Using our models, we predict how binding equilibria and kinetics depend on the distribution of cohesive blocks in the FG Nup sequences and of the binding pockets at the NTR surface, with multivalency playing a key role. Finally, we observe that single-molecule binding kinetics has a rather minor influence on the diffusion of NTRs in polymer melts consisting of FG-Nup-like sequences.}, author = {Davis, Luke K. and Šarić, Anđela and Hoogenboom, Bart W. and Zilman, Anton}, issn = {0006-3495}, journal = {Biophysical Journal}, keywords = {biophysics}, number = {9}, pages = {1565--1577}, publisher = {Elsevier}, title = {{Physical modeling of multivalent interactions in the nuclear pore complex}}, doi = {10.1016/j.bpj.2021.01.039}, volume = {120}, year = {2021}, } @article{9350, abstract = {Intercellular adhesion is the key to multicellularity, and its malfunction plays an important role in various developmental and disease-related processes. Although it has been intensively studied by both biologists and physicists, a commonly accepted definition of cell-cell adhesion is still being debated. Cell-cell adhesion has been described at the molecular scale as a function of adhesion receptors controlling binding affinity, at the cellular scale as resistance to detachment forces or modulation of surface tension, and at the tissue scale as a regulator of cellular rearrangements and morphogenesis. In this review, we aim to summarize and discuss recent advances in the molecular, cellular, and theoretical description of cell-cell adhesion, ranging from biomimetic models to the complexity of cells and tissues in an organismal context. In particular, we will focus on cadherin-mediated cell-cell adhesion and the role of adhesion signaling and mechanosensation therein, two processes central for understanding the biological and physical basis of cell-cell adhesion.}, author = {Arslan, Feyza N and Eckert, Julia and Schmidt, Thomas and Heisenberg, Carl-Philipp J}, issn = {1542-0086}, journal = {Biophysical Journal}, pages = {4182--4192}, publisher = {Biophysical Society}, title = {{Holding it together: when cadherin meets cadherin}}, doi = {10.1016/j.bpj.2021.03.025}, volume = {120}, year = {2021}, } @article{10346, abstract = {One of the most robust examples of self-assembly in living organisms is the formation of collagen architectures. Collagen type I molecules are a crucial component of the extracellular matrix, where they self-assemble into fibrils of well-defined axial striped patterns. This striped fibrillar pattern is preserved across the animal kingdom and is important for the determination of cell phenotype, cell adhesion, and tissue regulation and signaling. The understanding of the physical processes that determine such a robust morphology of self-assembled collagen fibrils is currently almost completely missing. Here, we develop a minimal coarse-grained computational model to identify the physical principles of the assembly of collagen-mimetic molecules. We find that screened electrostatic interactions can drive the formation of collagen-like filaments of well-defined striped morphologies. The fibril axial pattern is determined solely by the distribution of charges on the molecule and is robust to the changes in protein concentration, monomer rigidity, and environmental conditions. We show that the striped fibrillar pattern cannot be easily predicted from the interactions between two monomers but is an emergent result of multibody interactions. Our results can help address collagen remodeling in diseases and aging and guide the design of collagen scaffolds for biotechnological applications.}, author = {Hafner, Anne E. and Gyori, Noemi G. and Bench, Ciaran A. and Davis, Luke K. and Šarić, Anđela}, issn = {0006-3495}, journal = {Biophysical Journal}, keywords = {biophysics}, number = {9}, pages = {1791--1799}, publisher = {Cell Press}, title = {{Modeling fibrillogenesis of collagen-mimetic molecules}}, doi = {10.1016/j.bpj.2020.09.013}, volume = {119}, year = {2020}, } @article{10126, author = {Vahid Belarghou, Afshin and Šarić, Anđela and Idema, Timon}, issn = {0006-3495}, journal = {Biophysical Journal}, keywords = {biophysics}, number = {3}, publisher = {Elsevier }, title = {{Curvature mediated interactions in highly curved membranes}}, doi = {10.1016/j.bpj.2016.11.2123}, volume = {112}, year = {2017}, } @article{8444, abstract = {Biophysical investigation of membrane proteins generally requires their extraction from native sources using detergents, a step that can lead, possibly irreversibly, to protein denaturation. The propensity of dodecylphosphocholine (DPC), a detergent widely utilized in NMR studies of membrane proteins, to distort their structure has been the subject of much controversy. It has been recently proposed that the binding specificity of the yeast mitochondrial ADP/ATP carrier (yAAC3) toward cardiolipins is preserved in DPC, thereby suggesting that DPC is a suitable environment in which to study membrane proteins. In this communication, we used all-atom molecular dynamics simulations to investigate the specific binding of cardiolipins to yAAC3. Our data demonstrate that the interaction interface observed in a native-like environment differs markedly from that inferred from an NMR investigation in DPC, implying that in this detergent, the protein structure is distorted. We further investigated yAAC3 solubilized in DPC and in the milder dodecylmaltoside with thermal-shift assays. The loss of thermal transition observed in DPC confirms that the protein is no longer properly folded in this environment.}, author = {Dehez, François and Schanda, Paul and King, Martin S. and Kunji, Edmund R.S. and Chipot, Christophe}, issn = {0006-3495}, journal = {Biophysical Journal}, keywords = {Biophysics}, number = {11}, pages = {2311--2315}, publisher = {Elsevier}, title = {{Mitochondrial ADP/ATP carrier in dodecylphosphocholine binds cardiolipins with non-native affinity}}, doi = {10.1016/j.bpj.2017.09.019}, volume = {113}, year = {2017}, } @article{14308, abstract = {Here we describe an approach to bottom-up fabrication with nanometer-precision that allows integrating the functional diversity of proteins in designed three-dimensional structural frameworks. We reimagined the successful DNA origami design principle using a set of custom staple proteins to fold a double-stranded DNA template into a user-defined shape. Each staple protein recognizes two distinct double-helical DNA sequences and can carry additional functionalities. The staple proteins we present here are based on the transcription activator-like (TAL) effector proteins. Due to their repetitive structure these proteins offer a unique programmability that enables us to construct numerous staple proteins targeting any desired DNA sequence. Our approach is general, meaning that many different objects may be created using the same set of rules, and it is modular, because components can be modified or exchanged individually. We present rules for constructing megadalton-scale DNA-protein hybrid nanostructures; introduce important structural motifs, such as curvature, corners, and vertices; describe principles for creating multi-layer DNA-protein objects with enhanced rigidity; and demonstrate the possibility to combine our DNA-protein hybrid origami with conventional DNA nanotechnology. Since all components can be encoded genetically, our structures should be amenable to biotechnological mass-production. Moreover, since the target objects can self-assemble at room temperature in near-physiological buffer, our hybrid origami may also provide an attractive method to realize positioning and scaffolding tasks in vivo. We expect our method to find application both in scaffolding protein functionalities and in manipulating the spatial arrangement of genomic DNA.}, author = {Praetorius, Florian M and Dietz, Hendrik}, issn = {0006-3495}, journal = {Biophysical Journal}, keywords = {Biophysics}, number = {3}, publisher = {Elsevier}, title = {{Genetically encoded DNA-protein hybrid origami}}, doi = {10.1016/j.bpj.2016.11.171}, volume = {112}, year = {2017}, } @article{11088, abstract = {The crowded intracellular environment poses a formidable challenge to experimental and theoretical analyses of intracellular transport mechanisms. Our measurements of single-particle trajectories in cytoplasm and their random-walk interpretations elucidate two of these mechanisms: molecular diffusion in crowded environments and cytoskeletal transport along microtubules. We employed acousto-optic deflector microscopy to map out the three-dimensional trajectories of microspheres migrating in the cytosolic fraction of a cellular extract. Classical Brownian motion (BM), continuous time random walk, and fractional BM were alternatively used to represent these trajectories. The comparison of the experimental and numerical data demonstrates that cytoskeletal transport along microtubules and diffusion in the cytosolic fraction exhibit anomalous (nonFickian) behavior and posses statistically distinct signatures. Among the three random-walk models used, continuous time random walk provides the best representation of diffusion, whereas microtubular transport is accurately modeled with fractional BM.}, author = {Regner, Benjamin M. and Vučinić, Dejan and Domnisoru, Cristina and Bartol, Thomas M. and HETZER, Martin W and Tartakovsky, Daniel M. and Sejnowski, Terrence J.}, issn = {0006-3495}, journal = {Biophysical Journal}, keywords = {Biophysics}, number = {8}, pages = {1652--1660}, publisher = {Elsevier}, title = {{Anomalous diffusion of single particles in cytoplasm}}, doi = {10.1016/j.bpj.2013.01.049}, volume = {104}, year = {2013}, } @article{6496, abstract = {We report the switching behavior of the full bacterial flagellum system that includes the filament and the motor in wild-type Escherichia coli cells. In sorting the motor behavior by the clockwise bias, we find that the distributions of the clockwise (CW) and counterclockwise (CCW) intervals are either exponential or nonexponential with long tails. At low bias, CW intervals are exponentially distributed and CCW intervals exhibit long tails. At intermediate CW bias (0.5) both CW and CCW intervals are mainly exponentially distributed. A simple model suggests that these two distinct switching behaviors are governed by the presence of signaling noise within the chemotaxis network. Low noise yields exponentially distributed intervals, whereas large noise yields nonexponential behavior with long tails. These drastically different motor statistics may play a role in optimizing bacterial behavior for a wide range of environmental conditions.}, author = {Park, Heungwon and Oikonomou, Panos and Guet, Calin C and Cluzel, Philippe}, issn = {0006-3495}, journal = {Biophysical Journal}, number = {10}, pages = {2336--2340}, publisher = {Elsevier}, title = {{Noise underlies switching behavior of the bacterial flagellum}}, doi = {10.1016/j.bpj.2011.09.040}, volume = {101}, year = {2011}, } @article{3493, abstract = {Although agonists and competitive antagonists presumably occupy overlapping binding sites on ligand-gated channels, these interactions cannot be identical because agonists cause channel opening whereas antagonists do not. One explanation is that only agonist binding performs enough work on the receptor to cause the conformational changes that lead to gating. This idea is supported by agonist binding rates at GABAA and nicotinic acetylcholine receptors that are slower than expected for a diffusion-limited process, suggesting that agonist binding involves an energy-requiring event. This hypothesis predicts that competitive antagonist binding should require less activation energy than agonist binding. To test this idea, we developed a novel deconvolution-based method to compare binding and unbinding kinetics of GABAA receptor agonists and antagonists in outside-out patches from rat hippocampal neurons. Agonist and antagonist unbinding rates were steeply correlated with affinity. Unlike the agonists, three of the four antagonists tested had binding rates that were fast, independent of affinity, and could be accounted for by diffusion- and dehydration-limited processes. In contrast, agonist binding involved additional energy-requiring steps, consistent with the idea that channel gating is initiated by agonist-triggered movements within the ligand binding site. Antagonist binding does not appear to produce such movements, and may in fact prevent them.}, author = {Jones, M.V and Jonas, Peter M and Sahara, Y. and Westbrook, G.}, issn = {0006-3495}, journal = {Biophysical Journal}, number = {5}, pages = {2660 -- 2670}, publisher = {Biophysical Society}, title = {{Microscopic kinetics and energetics distinguish GABAA receptor agonists from antagonists}}, doi = {10.1016/S0006-3495(01)75909-7 }, volume = {81}, year = {2001}, }