1
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Lee AA, Kim NH, Alvarez S, Ren H, DeGrandchamp JB, Lew LJN, Groves JT. Bimodality in Ras signaling originates from processivity of the Ras activator SOS without deterministic bistability. SCIENCE ADVANCES 2024; 10:eadi0707. [PMID: 38905351 PMCID: PMC11192083 DOI: 10.1126/sciadv.adi0707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2023] [Accepted: 05/15/2024] [Indexed: 06/23/2024]
Abstract
Ras is a small GTPase that is central to important functional decisions in diverse cell types. An important aspect of Ras signaling is its ability to exhibit bimodal or switch-like activity. We describe the total reconstitution of a receptor-mediated Ras activation-deactivation reaction catalyzed by SOS and p120-RasGAP on supported lipid membrane microarrays. The results reveal a bimodal Ras activation response, which is not a result of deterministic bistability but is rather driven by the distinct processivity of the Ras activator, SOS. Furthermore, the bimodal response is controlled by the condensation state of the scaffold protein, LAT, to which SOS is recruited. Processivity-driven bimodality leads to stochastic bursts of Ras activation even under strongly deactivating conditions. This behavior contrasts deterministic bistability and may be more resistant to pharmacological inhibition.
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Affiliation(s)
- Albert A. Lee
- Department of Chemistry, University of California, Berkeley, CA 94720, USA
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
| | - Neil H. Kim
- Department of Chemistry, University of California, Berkeley, CA 94720, USA
| | - Steven Alvarez
- Department of Chemistry, University of California, Berkeley, CA 94720, USA
- Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA
| | - He Ren
- Department of Chemistry, University of California, Berkeley, CA 94720, USA
| | | | - L. J. Nugent Lew
- Department of Chemistry, University of California, Berkeley, CA 94720, USA
| | - Jay T. Groves
- Department of Chemistry, University of California, Berkeley, CA 94720, USA
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2
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Schmidt HN, Gaetjens TK, Leopin EE, Abel SM. Compartmental exchange regulates steady states and stochastic switching of a phosphorylation network. Biophys J 2024; 123:598-609. [PMID: 38317416 PMCID: PMC10938077 DOI: 10.1016/j.bpj.2024.01.039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2023] [Revised: 01/24/2024] [Accepted: 01/31/2024] [Indexed: 02/07/2024] Open
Abstract
The phosphoregulation of proteins with multiple phosphorylation sites is governed by biochemical reaction networks that can exhibit multistable behavior. However, the behavior of such networks is typically studied in a single reaction volume, while cells are spatially organized into compartments that can exchange proteins. In this work, we use stochastic simulations to study the impact of compartmentalization on a two-site phosphorylation network. We characterize steady states and fluctuation-driven transitions between them as a function of the rate of protein exchange between two compartments. Surprisingly, the average time spent in a state before stochastically switching to another depends nonmonotonically on the protein exchange rate, with the most frequent switching occurring at intermediate exchange rates. At sufficiently small exchange rates, the state of the system and mean switching time are controlled largely by fluctuations in the balance of enzymes in each compartment. This leads to negatively correlated states in the compartments. For large exchange rates, the two compartments behave as a single effective compartment. However, when the compartmental volumes are unequal, the behavior differs from a single compartment with the same total volume. These results demonstrate that exchange of proteins between distinct compartments can regulate the emergent behavior of a common signaling motif.
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Affiliation(s)
- Hannah N Schmidt
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee
| | - Thomas K Gaetjens
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee
| | - Emily E Leopin
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee
| | - Steven M Abel
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee.
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3
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Scott ZC, Koning K, Vanderwerp M, Cohen L, Westrate LM, Koslover EF. Endoplasmic reticulum network heterogeneity guides diffusive transport and kinetics. Biophys J 2023; 122:3191-3205. [PMID: 37401053 PMCID: PMC10432226 DOI: 10.1016/j.bpj.2023.06.022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Revised: 05/17/2023] [Accepted: 06/28/2023] [Indexed: 07/05/2023] Open
Abstract
The endoplasmic reticulum (ER) is a dynamic network of interconnected sheets and tubules that orchestrates the distribution of lipids, ions, and proteins throughout the cell. The impact of its complex, dynamic morphology on its function as an intracellular transport hub remains poorly understood. To elucidate the functional consequences of ER network structure and dynamics, we quantify how the heterogeneity of the peripheral ER in COS7 cells affects diffusive protein transport. In vivo imaging of photoactivated ER membrane proteins demonstrates their nonuniform spreading to adjacent regions, in a manner consistent with simulations of diffusing particles on extracted network structures. Using a minimal network model to represent tubule rearrangements, we demonstrate that ER network dynamics are sufficiently slow to have little effect on diffusive protein transport. Furthermore, stochastic simulations reveal a novel consequence of ER network heterogeneity: the existence of "hot spots" where sparse diffusive reactants are more likely to find one another. ER exit sites, specialized domains regulating cargo export from the ER, are shown to be disproportionately located in highly accessible regions, further from the outer boundary of the cell. Combining in vivo experiments with analytic calculations, quantitative image analysis, and computational modeling, we demonstrate how structure guides diffusive protein transport and reactions in the ER.
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Affiliation(s)
| | - Katherine Koning
- Department of Chemistry and Biochemistry, Calvin University, Grand Rapids, Michigan
| | - Molly Vanderwerp
- Department of Chemistry and Biochemistry, Calvin University, Grand Rapids, Michigan
| | | | - Laura M Westrate
- Department of Chemistry and Biochemistry, Calvin University, Grand Rapids, Michigan
| | - Elena F Koslover
- Department of Physics, University of California, San Diego, La Jolla, California.
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4
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Leonard TA, Loose M, Martens S. The membrane surface as a platform that organizes cellular and biochemical processes. Dev Cell 2023; 58:1315-1332. [PMID: 37419118 DOI: 10.1016/j.devcel.2023.06.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2023] [Revised: 04/22/2023] [Accepted: 06/08/2023] [Indexed: 07/09/2023]
Abstract
Membranes are essential for life. They act as semi-permeable boundaries that define cells and organelles. In addition, their surfaces actively participate in biochemical reaction networks, where they confine proteins, align reaction partners, and directly control enzymatic activities. Membrane-localized reactions shape cellular membranes, define the identity of organelles, compartmentalize biochemical processes, and can even be the source of signaling gradients that originate at the plasma membrane and reach into the cytoplasm and nucleus. The membrane surface is, therefore, an essential platform upon which myriad cellular processes are scaffolded. In this review, we summarize our current understanding of the biophysics and biochemistry of membrane-localized reactions with particular focus on insights derived from reconstituted and cellular systems. We discuss how the interplay of cellular factors results in their self-organization, condensation, assembly, and activity, and the emergent properties derived from them.
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Affiliation(s)
- Thomas A Leonard
- Max Perutz Labs, Vienna Biocenter Campus (VBC), Dr. Bohr-Gasse 9, 1030, Vienna, Austria; Medical University of Vienna, Center for Medical Biochemistry, Dr. Bohr-Gasse 9, 1030, Vienna, Austria.
| | - Martin Loose
- Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria.
| | - Sascha Martens
- Max Perutz Labs, Vienna Biocenter Campus (VBC), Dr. Bohr-Gasse 9, 1030, Vienna, Austria; University of Vienna, Center for Molecular Biology, Department of Biochemistry and Cell Biology, Dr. Bohr-Gasse 9, 1030, Vienna, Austria.
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5
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Lee AA, Kim NH, Alvarez S, Ren H, DeGrandchamp JB, Lew LJN, Groves JT. Bimodality in Ras signaling originates from processivity of the Ras activator SOS without classic kinetic bistability. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.17.549263. [PMID: 37503094 PMCID: PMC10370109 DOI: 10.1101/2023.07.17.549263] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
Ras is a small GTPase that is central to important functional decisions in diverse cell types. An important aspect of Ras signaling is its ability to exhibit bimodal, or switch-like activity. We describe the total reconstitution of a receptor-mediated Ras activation-deactivation reaction catalyzed by SOS and p120-RasGAP on supported lipid membrane microarrays. The results reveal a bimodal Ras activation response, which is not a result of classic kinetic bistability, but is rather driven by the distinct processivity of the Ras activator, SOS. Furthermore, the bimodal response is controlled by the condensation state of the scaffold protein, LAT, to which SOS is recruited. Processivity-driven bimodality leads to stochastic bursts of Ras activation even under strongly deactivating conditions. This behavior contrasts classic kinetic bistability and is distinctly more resistant to pharmacological inhibition.
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6
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Loose M, Auer A, Brognara G, Budiman HR, Kowalski L, Matijević I. In vitro
reconstitution of small
GTPase
regulation. FEBS Lett 2022; 597:762-777. [PMID: 36448231 DOI: 10.1002/1873-3468.14540] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 10/27/2022] [Accepted: 11/07/2022] [Indexed: 12/05/2022]
Abstract
Small GTPases play essential roles in the organization of eukaryotic cells. In recent years, it has become clear that their intracellular functions result from intricate biochemical networks of the GTPase and their regulators that dynamically bind to a membrane surface. Due to the inherent complexities of their interactions, however, revealing the underlying mechanisms of action is often difficult to achieve from in vivo studies. This review summarizes in vitro reconstitution approaches developed to obtain a better mechanistic understanding of how small GTPase activities are regulated in space and time.
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Affiliation(s)
- Martin Loose
- Institute of Science and Technology Austria (ISTA) Klosterneuburg Austria
| | - Albert Auer
- Institute of Science and Technology Austria (ISTA) Klosterneuburg Austria
| | - Gabriel Brognara
- Institute of Science and Technology Austria (ISTA) Klosterneuburg Austria
| | | | - Lukasz Kowalski
- Institute of Science and Technology Austria (ISTA) Klosterneuburg Austria
| | - Ivana Matijević
- Institute of Science and Technology Austria (ISTA) Klosterneuburg Austria
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7
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Abstract
Transport of intracellular components relies on a variety of active and passive mechanisms, ranging from the diffusive spreading of small molecules over short distances to motor-driven motion across long distances. The cell-scale behavior of these mechanisms is fundamentally dependent on the morphology of the underlying cellular structures. Diffusion-limited reaction times can be qualitatively altered by the presence of occluding barriers or by confinement in complex architectures, such as those of reticulated organelles. Motor-driven transport is modulated by the architecture of cytoskeletal filaments that serve as transport highways. In this review, we discuss the impact of geometry on intracellular transport processes that fulfill a broad range of functional objectives, including delivery, distribution, and sorting of cellular components. By unraveling the interplay between morphology and transport efficiency, we aim to elucidate key structure-function relationships that govern the architecture of transport systems at the cellular scale. Expected final online publication date for the Annual Review of Biophysics, Volume 51 is May 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Affiliation(s)
- Anamika Agrawal
- Department of Physics, University of California, San Diego, La Jolla, California, USA;
| | - Zubenelgenubi C Scott
- Department of Physics, University of California, San Diego, La Jolla, California, USA;
| | - Elena F Koslover
- Department of Physics, University of California, San Diego, La Jolla, California, USA;
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8
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Romero-Campos HE, Dupont G, Gonzalez-Velez V. On the Electrophysiological Component of Pancreatic Alpha-Cell Models. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2021; 2021:4408-4411. [PMID: 34892197 DOI: 10.1109/embc46164.2021.9630329] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Glucagon, the main hormone responsible for increasing blood glucose levels, is secreted by pancreatic alphacells in a Ca2+ dependent process associated to membrane potential oscillations developed by the dynamic operation of K+, Na+ and Ca2+ channels. The mechanisms behind membrane potential and Ca2+ oscillations in alpha-cells are still under debate, and some new research works have used alpha-cell models to describe electrical activity. In this paper we studied the dynamics of electrical activity of three alpha-cell models using the Lead Potential Analysis method and Bifurcation Diagrams. Our aim is to highlight the differences in their dynamic behavior and therefore, in their response to glucose. Both issues are relevant to understand the stimulus-secretion coupling in alpha-cells and then, the mechanisms behind their dysregulation in Type 2 Diabetes.Clinical Relevance - A reliable description of the electrophysiological mechanisms in pancreatic alpha-cells is key to understand and treat the dysregulation of these cells in patients with Type 2 Diabetes.
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9
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Koch D, Alexandrovich A, Funk F, Kho AL, Schmitt JP, Gautel M. Molecular noise filtering in the β-adrenergic signaling network by phospholamban pentamers. Cell Rep 2021; 36:109448. [PMID: 34320358 PMCID: PMC8333238 DOI: 10.1016/j.celrep.2021.109448] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Revised: 04/16/2021] [Accepted: 07/05/2021] [Indexed: 02/07/2023] Open
Abstract
Phospholamban (PLN) is an important regulator of cardiac calcium handling due to its ability to inhibit the calcium ATPase SERCA. β-Adrenergic stimulation reverses SERCA inhibition via PLN phosphorylation and facilitates fast calcium reuptake. PLN also forms pentamers whose physiological significance has remained elusive. Using mathematical modeling combined with biochemical and cell biological experiments, we show that pentamers regulate both the dynamics and steady-state levels of monomer phosphorylation. Substrate competition by pentamers and a feed-forward loop involving inhibitor-1 can delay monomer phosphorylation by protein kinase A (PKA), whereas cooperative pentamer dephosphorylation enables bistable PLN steady-state phosphorylation. Simulations show that phosphorylation delay and bistability act as complementary filters that reduce the effect of random fluctuations in PKA activity, thereby ensuring consistent monomer phosphorylation and SERCA activity despite noisy upstream signals. Preliminary analyses suggest that the PLN mutation R14del could impair noise filtering, offering a new perspective on how this mutation causes cardiac arrhythmias.
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Affiliation(s)
- Daniel Koch
- Randall Centre for Cell and Molecular Biophysics, King's College London, SE1 1UL London, UK.
| | | | - Florian Funk
- Institute of Pharmacology and Clinical Pharmacology, and Cardiovascular Research Institute Düsseldorf (CARID), University Hospital Düsseldorf, 40225 Düsseldorf, Germany
| | - Ay Lin Kho
- Randall Centre for Cell and Molecular Biophysics, King's College London, SE1 1UL London, UK
| | - Joachim P Schmitt
- Institute of Pharmacology and Clinical Pharmacology, and Cardiovascular Research Institute Düsseldorf (CARID), University Hospital Düsseldorf, 40225 Düsseldorf, Germany
| | - Mathias Gautel
- Randall Centre for Cell and Molecular Biophysics, King's College London, SE1 1UL London, UK
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10
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Scott ZC, Brown AI, Mogre SS, Westrate LM, Koslover EF. Diffusive search and trajectories on tubular networks: a propagator approach. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2021; 44:80. [PMID: 34143351 PMCID: PMC8213674 DOI: 10.1140/epje/s10189-021-00083-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Accepted: 05/25/2021] [Indexed: 05/11/2023]
Abstract
Several organelles in eukaryotic cells, including mitochondria and the endoplasmic reticulum, form interconnected tubule networks extending throughout the cell. These tubular networks host many biochemical pathways that rely on proteins diffusively searching through the network to encounter binding partners or localized target regions. Predicting the behavior of such pathways requires a quantitative understanding of how confinement to a reticulated structure modulates reaction kinetics. In this work, we develop both exact analytical methods to compute mean first passage times and efficient kinetic Monte Carlo algorithms to simulate trajectories of particles diffusing in a tubular network. Our approach leverages exact propagator functions for the distribution of transition times between network nodes and allows large simulation time steps determined by the network structure. The methodology is applied to both synthetic planar networks and organelle network structures, demonstrating key general features such as the heterogeneity of search times in different network regions and the functional advantage of broadly distributing target sites throughout the network. The proposed algorithms pave the way for future exploration of the interrelationship between tubular network structure and biomolecular reaction kinetics.
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Affiliation(s)
- Zubenelgenubi C Scott
- Department of Physics, University of California, San Diego, La Jolla, CA, 92093, USA
| | - Aidan I Brown
- Department of Physics, Ryerson University, Toronto, Canada
| | - Saurabh S Mogre
- Department of Physics, University of California, San Diego, La Jolla, CA, 92093, USA
| | - Laura M Westrate
- Department of Chemistry and Biochemistry, Calvin University, Grand Rapids, MI, 49546, USA
| | - Elena F Koslover
- Department of Physics, University of California, San Diego, La Jolla, CA, 92093, USA.
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11
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Mishra B, Johnson ME. Speed limits of protein assembly with reversible membrane localization. J Chem Phys 2021; 154:194101. [PMID: 34240891 PMCID: PMC8131109 DOI: 10.1063/5.0045867] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Accepted: 04/26/2021] [Indexed: 12/15/2022] Open
Abstract
Protein assembly is often studied in a three-dimensional solution, but a significant fraction of binding events involve proteins that can reversibly bind and diffuse along a two-dimensional surface. In a recent study, we quantified how proteins can exploit the reduced dimensionality of the membrane to trigger complex formation. Here, we derive a single expression for the characteristic timescale of this multi-step assembly process, where the change in dimensionality renders rates and concentrations effectively time-dependent. We find that proteins can accelerate dimer formation due to an increase in relative concentration, driving more frequent collisions, which often win out over slow-downs due to diffusion. Our model contains two protein populations that dimerize with one another and use a distinct site to bind membrane lipids, creating a complex reaction network. However, by identifying two major rate-limiting pathways to reach an equilibrium steady-state, we derive an excellent approximation for the mean first passage time when lipids are in abundant supply. Our theory highlights how the "sticking rate" or effective adsorption coefficient of the membrane is central in controlling timescales. We also derive a corrected localization rate to quantify how the geometry of the system and diffusion can reduce rates of membrane localization. We validate and test our results using kinetic and particle-based reaction-diffusion simulations. Our results establish how the speed of key assembly steps can shift by orders-of-magnitude when membrane localization is possible, which is critical to understanding mechanisms used in cells.
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Affiliation(s)
- Bhavya Mishra
- TC Jenkins Department of Biophysics, Johns Hopkins University, 3400 N Charles St., Baltimore, Maryland 21218, USA
| | - Margaret E. Johnson
- TC Jenkins Department of Biophysics, Johns Hopkins University, 3400 N Charles St., Baltimore, Maryland 21218, USA
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12
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Johnson ME, Chen A, Faeder JR, Henning P, Moraru II, Meier-Schellersheim M, Murphy RF, Prüstel T, Theriot JA, Uhrmacher AM. Quantifying the roles of space and stochasticity in computer simulations for cell biology and cellular biochemistry. Mol Biol Cell 2021; 32:186-210. [PMID: 33237849 PMCID: PMC8120688 DOI: 10.1091/mbc.e20-08-0530] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Revised: 10/13/2020] [Accepted: 11/17/2020] [Indexed: 12/29/2022] Open
Abstract
Most of the fascinating phenomena studied in cell biology emerge from interactions among highly organized multimolecular structures embedded into complex and frequently dynamic cellular morphologies. For the exploration of such systems, computer simulation has proved to be an invaluable tool, and many researchers in this field have developed sophisticated computational models for application to specific cell biological questions. However, it is often difficult to reconcile conflicting computational results that use different approaches to describe the same phenomenon. To address this issue systematically, we have defined a series of computational test cases ranging from very simple to moderately complex, varying key features of dimensionality, reaction type, reaction speed, crowding, and cell size. We then quantified how explicit spatial and/or stochastic implementations alter outcomes, even when all methods use the same reaction network, rates, and concentrations. For simple cases, we generally find minor differences in solutions of the same problem. However, we observe increasing discordance as the effects of localization, dimensionality reduction, and irreversible enzymatic reactions are combined. We discuss the strengths and limitations of commonly used computational approaches for exploring cell biological questions and provide a framework for decision making by researchers developing new models. As computational power and speed continue to increase at a remarkable rate, the dream of a fully comprehensive computational model of a living cell may be drawing closer to reality, but our analysis demonstrates that it will be crucial to evaluate the accuracy of such models critically and systematically.
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Affiliation(s)
- M. E. Johnson
- Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD, 21218
| | - A. Chen
- Thomas C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, MD, 21218
| | - J. R. Faeder
- Department of Computational and Systems Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, 15260
| | - P. Henning
- Institute for Visual and Analytic Computing, University of Rostock, 18055 Rostock, Germany
| | - I. I. Moraru
- Department of Cell Biology, Center for Cell Analysis and Modeling, University of Connecticut Health Center, Farmington, CT 06030
| | - M. Meier-Schellersheim
- Laboratory of Immune System Biology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892
| | - R. F. Murphy
- Computational Biology Department, Department of Biological Sciences, Department of Biomedical Engineering, Machine Learning Department, Carnegie Mellon University, Pittsburgh, PA 15289
| | - T. Prüstel
- Laboratory of Immune System Biology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892
| | - J. A. Theriot
- Department of Biology and Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195
| | - A. M. Uhrmacher
- Institute for Visual and Analytic Computing, University of Rostock, 18055 Rostock, Germany
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13
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S Mogre S, Brown AI, Koslover EF. Getting around the cell: physical transport in the intracellular world. Phys Biol 2020; 17:061003. [PMID: 32663814 DOI: 10.1088/1478-3975/aba5e5] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Eukaryotic cells face the challenging task of transporting a variety of particles through the complex intracellular milieu in order to deliver, distribute, and mix the many components that support cell function. In this review, we explore the biological objectives and physical mechanisms of intracellular transport. Our focus is on cytoplasmic and intra-organelle transport at the whole-cell scale. We outline several key biological functions that depend on physically transporting components across the cell, including the delivery of secreted proteins, support of cell growth and repair, propagation of intracellular signals, establishment of organelle contacts, and spatial organization of metabolic gradients. We then review the three primary physical modes of transport in eukaryotic cells: diffusive motion, motor-driven transport, and advection by cytoplasmic flow. For each mechanism, we identify the main factors that determine speed and directionality. We also highlight the efficiency of each transport mode in fulfilling various key objectives of transport, such as particle mixing, directed delivery, and rapid target search. Taken together, the interplay of diffusion, molecular motors, and flows supports the intracellular transport needs that underlie a broad variety of biological phenomena.
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Affiliation(s)
- Saurabh S Mogre
- Department of Physics, University of California, San Diego, San Diego, California 92093, United States of America
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14
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Stolerman LM, Getz M, Smith SGL, Holst M, Rangamani P. Stability Analysis of a Bulk-Surface Reaction Model for Membrane Protein Clustering. Bull Math Biol 2020; 82:30. [PMID: 32025918 DOI: 10.1007/s11538-020-00703-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Accepted: 01/22/2020] [Indexed: 12/11/2022]
Abstract
Protein aggregation on the plasma membrane (PM) is of critical importance to many cellular processes such as cell adhesion, endocytosis, fibrillar conformation, and vesicle transport. Lateral diffusion of protein aggregates or clusters on the surface of the PM plays an important role in governing their heterogeneous surface distribution. However, the stability behavior of the surface distribution of protein aggregates remains poorly understood. Therefore, understanding the spatial patterns that can emerge on the PM solely through protein-protein interaction, lateral diffusion, and feedback is an important step toward a complete description of the mechanisms behind protein clustering on the cell surface. In this work, we investigate the pattern formation of a reaction-diffusion model that describes the dynamics of a system of ligand-receptor complexes. The purely diffusive ligand in the cytosol can bind receptors in the PM and the resultant ligand-receptor complexes not only diffuse laterally but can also form clusters resulting in different oligomers. Finally, the largest oligomers recruit ligands from the cytosol using positive feedback. From a methodological viewpoint, we provide theoretical estimates for diffusion-driven instabilities of the protein aggregates based on the Turing mechanism. Our main result is a threshold phenomenon, in which a sufficiently high recruitment of ligands promotes the input of new monomeric components and consequently drives the formation of a single-patch spatially heterogeneous steady state.
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Affiliation(s)
- Lucas M Stolerman
- Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA, 92093-0411, USA
| | - Michael Getz
- Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA, 92093-0411, USA
| | - Stefan G Llewellyn Smith
- Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA, 92093-0411, USA.,Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, 92093-0213, USA
| | - Michael Holst
- Department of Mathematics, University of California, San Diego, La Jolla, CA, 92093-0112, USA.,Department of Physics, University of California, San Diego, La Jolla, CA, 92093-0424, USA
| | - Padmini Rangamani
- Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA, 92093-0411, USA.
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15
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Zhang Y, Clemens L, Goyette J, Allard J, Dushek O, Isaacson SA. The Influence of Molecular Reach and Diffusivity on the Efficacy of Membrane-Confined Reactions. Biophys J 2019; 117:1189-1201. [PMID: 31543263 PMCID: PMC6818170 DOI: 10.1016/j.bpj.2019.08.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Revised: 07/30/2019] [Accepted: 08/22/2019] [Indexed: 11/15/2022] Open
Abstract
Signaling by surface receptors often relies on tethered reactions whereby an enzyme bound to the cytoplasmic tail of a receptor catalyzes reactions on substrates within reach. The overall length and stiffness of the receptor tail, the enzyme, and the substrate determine a biophysical parameter termed the molecular reach of the reaction. This parameter determines the probability that the receptor-tethered enzyme will contact the substrate in the volume proximal to the membrane when separated by different distances within the membrane plane. In this work, we develop particle-based stochastic reaction-diffusion models to study the interplay between molecular reach and diffusion. We find that increasing the molecular reach can increase reaction efficacy for slowly diffusing receptors, whereas for rapidly diffusing receptors, increasing molecular reach reduces reaction efficacy. In contrast, if reactions are forced to take place within the two-dimensional plasma membrane instead of the three-dimensional volume proximal to it or if molecules diffuse in three dimensions, increasing molecular reach increases reaction efficacy for all diffusivities. We show results in the context of immune checkpoint receptors (PD-1 dephosphorylating CD28), a standard opposing kinase-phosphatase reaction, and a minimal two-particle model. The work highlights the importance of the three-dimensional nature of many two-dimensional membrane-confined interactions, illustrating a role for molecular reach in controlling biochemical reactions.
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Affiliation(s)
- Ying Zhang
- Department of Mathematics and Statistics, Boston University, Boston, Massachusetts
| | - Lara Clemens
- Center for Complex Biological Systems, University of California-Irvine, Irvine, California
| | - Jesse Goyette
- School of Medical Sciences, University of New South Wales, Sydney, Australia
| | - Jun Allard
- Center for Complex Biological Systems, University of California-Irvine, Irvine, California
| | - Omer Dushek
- Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom.
| | - Samuel A Isaacson
- Department of Mathematics and Statistics, Boston University, Boston, Massachusetts.
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16
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Pullen RH, Abel SM. Mechanical feedback enables catch bonds to selectively stabilize scanning microvilli at T-cell surfaces. Mol Biol Cell 2019; 30:2087-2095. [PMID: 31116687 PMCID: PMC6727777 DOI: 10.1091/mbc.e19-01-0048] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
T-cells use microvilli to search the surfaces of antigen-presenting cells for antigenic ligands. The active motion of scanning microvilli provides a force-generating mechanism that is intriguing in light of single-molecule experiments showing that applied forces increase the lifetimes of stimulatory receptor–ligand bonds (catch-bond behavior). In this work, we introduce a theoretical framework to explore the motion of a microvillar tip above an antigen-presenting surface when receptors on the tip stochastically bind to ligands on the surface and dissociate from them in a force-dependent manner. Forces on receptor-ligand bonds impact the motion of the microvillus, leading to feedback between binding and microvillar motion. We use computer simulations to show that the average microvillar velocity varies in a ligand-dependent manner; that catch bonds generate responses in which some microvilli almost completely stop, while others move with a broad distribution of velocities; and that the frequency of stopping depends on the concentration of stimulatory ligands. Typically, a small number of catch bonds initially immobilize the microvillus, after which additional bonds accumulate and increase the cumulative receptor-engagement time. Our results demonstrate that catch bonds can selectively slow and stabilize scanning microvilli, suggesting a physical mechanism that may contribute to antigen discrimination by T-cells.
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Affiliation(s)
- Robert H Pullen
- Department of Chemical and Biomolecular Engineering, National Institute for Mathematical and Biological Synthesis, University of Tennessee, Knoxville, TN 37996
| | - Steven M Abel
- Department of Chemical and Biomolecular Engineering, National Institute for Mathematical and Biological Synthesis, University of Tennessee, Knoxville, TN 37996
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17
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Cytosolic proteins can exploit membrane localization to trigger functional assembly. PLoS Comput Biol 2018; 14:e1006031. [PMID: 29505559 PMCID: PMC5854442 DOI: 10.1371/journal.pcbi.1006031] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2017] [Revised: 03/15/2018] [Accepted: 02/09/2018] [Indexed: 12/03/2022] Open
Abstract
Cell division, endocytosis, and viral budding would not function without the localization and assembly of protein complexes on membranes. What is poorly appreciated, however, is that by localizing to membranes, proteins search in a reduced space that effectively drives up concentration. Here we derive an accurate and practical analytical theory to quantify the significance of this dimensionality reduction in regulating protein assembly on membranes. We define a simple metric, an effective equilibrium constant, that allows for quantitative comparison of protein-protein interactions with and without membrane present. To test the importance of membrane localization for driving protein assembly, we collected the protein-protein and protein-lipid affinities, protein and lipid concentrations, and volume-to-surface-area ratios for 46 interactions between 37 membrane-targeting proteins in human and yeast cells. We find that many of the protein-protein interactions between pairs of proteins involved in clathrin-mediated endocytosis in human and yeast cells can experience enormous increases in effective protein-protein affinity (10–1000 fold) due to membrane localization. Localization of binding partners thus triggers robust protein complexation, suggesting that it can play an important role in controlling the timing of endocytic protein coat formation. Our analysis shows that several other proteins involved in membrane remodeling at various organelles have similar potential to exploit localization. The theory highlights the master role of phosphoinositide lipid concentration, the volume-to-surface-area ratio, and the ratio of 3D to 2D equilibrium constants in triggering (or preventing) constitutive assembly on membranes. Our simple model provides a novel quantitative framework for interpreting or designing in vitro experiments of protein complexation influenced by membrane binding. In a multitude of cellular processes, including cell division and endocytosis, proteins must bind to one another to form large multi-protein complexes. To initiate the formation of these critical multi-protein assemblies at the right time and the right place, the constituent proteins must be present at sufficient concentrations. We show here that membrane localization offers a powerful way of controlling protein concentrations by reducing the dimensionality of the protein’s search space. We present a simple and practical analytical theory that determines the significance of membrane localization for triggering protein-protein interactions. We show that protein binding partners will often form substantially more complexes when both partners can localize to surfaces, and thus localization can regulate the timing of multi-protein assembly. We collect in vitro binding data and cellular concentrations of proteins and lipids involved in pathways including clathrin-mediated endocytosis to demonstrate how cellular proteins could exploit membrane localization to regulate assembly.
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18
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Handy G, Lawley SD, Borisyuk A. Receptor recharge time drastically reduces the number of captured particles. PLoS Comput Biol 2018; 14:e1006015. [PMID: 29494590 PMCID: PMC5849338 DOI: 10.1371/journal.pcbi.1006015] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2017] [Revised: 03/13/2018] [Accepted: 02/01/2018] [Indexed: 11/18/2022] Open
Abstract
Many diverse biological systems are described by randomly moving particles that can be captured by traps in their environment. Examples include neurotransmitters diffusing in the synaptic cleft before binding to receptors and prey roaming an environment before capture by predators. In most cases, the traps cannot capture particles continuously. Rather, each trap must wait a transitory “recharge” time after capturing a particle before additional captures. This recharge time is often overlooked. In the case of instant recharge, the average number of particles captured before they escape grows linearly in the total number of particles. In stark contrast, we prove that for any nonzero recharge time, the average number of captured particles grows at most logarithmically in the total particle number. This is a fundamental effect of recharge, as it holds under very general assumptions on particle motion and spatial domain. Furthermore, we characterize the parameter regime in which a given recharge time will dramatically affect a system, allowing researchers to easily verify if they need to account for recharge in their specific system. Finally, we consider a few examples, including a neural system in which recharge reduces neurotransmitter bindings by several orders of magnitude. Consider particles that are released into an environment (think diffusing molecules or plankton), and suppose that there are traps in the environment. How many particles will be captured by the traps before they escape? In a standard model, the number of captured particles is proportional to the initial number released. In this paper, we show that for a more realistic model of a trap (one in which traps must recharge after every capture), the number of captures is proportional to the logarithm of the initial number released. That means that if 106 particles are released, only about 6 will be captured. We prove this result mathematically, and then consider a number of applications, including neuronal synapses and ambush predators.
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Affiliation(s)
- Gregory Handy
- Department of Mathematics, University of Utah, Salt Lake City, Utah, United States of America
| | - Sean D. Lawley
- Department of Mathematics, University of Utah, Salt Lake City, Utah, United States of America
- * E-mail:
| | - Alla Borisyuk
- Department of Mathematics, University of Utah, Salt Lake City, Utah, United States of America
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19
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Abstract
The behavior of many biochemical processes depends crucially on molecules rapidly rebinding after dissociating. In the case of multisite protein modification, the importance of rebinding has been demonstrated both experimentally and through several recent computational studies involving stochastic spatial simulations. As rebinding stems from spatio-temporal correlations, theorists have resorted to models that explicitly include space to properly account for the effects of rebinding. However, for reactions in three space dimensions it was recently shown that well-mixed ordinary differential equation (ODE) models can incorporate rebinding by adding connections to the reaction network. The rate constants for these new connections involve the probability that a pair of molecules rapidly rebinds after dissociation. In order to study biochemical reactions on membranes, in this paper we derive an explicit formula for this rebinding probability for reactions in two space dimensions. We show that ODE models can use the formula to replicate detailed stochastic spatial simulations, and that the formula can predict ultrasensitivity for reactions involving multisite modification of membrane-bound proteins. Further, we compute a new concentration-dependent rebinding probability for reactions in three space dimensions. Our analysis predicts that rebinding plays a much larger role in reactions on membranes compared to reactions in cytoplasm.
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Affiliation(s)
- Sean D Lawley
- Department of Mathematics, University of Utah, Salt Lake City, UT 84112 United States of America
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20
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Lawley SD, Keener JP. Including Rebinding Reactions in Well-Mixed Models of Distributive Biochemical Reactions. Biophys J 2017; 111:2317-2326. [PMID: 27851953 DOI: 10.1016/j.bpj.2016.10.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Revised: 10/06/2016] [Accepted: 10/11/2016] [Indexed: 11/28/2022] Open
Abstract
The behavior of biochemical reactions requiring repeated enzymatic substrate modification depends critically on whether the enzymes act processively or distributively. Whereas processive enzymes bind only once to a substrate before carrying out a sequence of modifications, distributive enzymes release the substrate after each modification and thus require repeated bindings. Recent experimental and computational studies have revealed that distributive enzymes can act processively due to rapid rebindings (so-called quasi-processivity). In this study, we derive an analytical estimate of the probability of rapid rebinding and show that well-mixed ordinary differential equation models can use this probability to quantitatively replicate the behavior of spatial models. Importantly, rebinding requires that connections be added to the well-mixed reaction network; merely modifying rate constants is insufficient. We then use these well-mixed models to suggest experiments to 1) detect quasi-processivity and 2) test the theory. Finally, we show that rapid rebindings drastically alter the reaction's Michaelis-Menten rate equations.
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Affiliation(s)
- Sean D Lawley
- Department of Mathematics, University of Utah, Salt Lake City, Utah
| | - James P Keener
- Department of Mathematics, University of Utah, Salt Lake City, Utah.
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21
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Sharma SK, Li S, Micic M, Orbulescu J, Weissbart D, Nakahara H, Shibata O, Leblanc RM. β-Galactosidase Langmuir Monolayer at Air/X-gal Subphase Interface. J Phys Chem B 2016; 120:12279-12286. [DOI: 10.1021/acs.jpcb.6b09020] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Shiv K. Sharma
- Department
of Chemistry, University of Miami, 1301 Memorial Drive, Coral Gables, Florida 33146, United States
| | - Shanghao Li
- Department
of Chemistry, University of Miami, 1301 Memorial Drive, Coral Gables, Florida 33146, United States
| | - Miodrag Micic
- MP Biomedicals LLC, 3 Hutton
Center, Santa Ana, California 92707, United States
- Department
of Engineering Design Technology, Cerritos College, 11110 Alondra
Boulevard, Norwalk, California 9265, United States
| | - Jhony Orbulescu
- MP Biomedicals LLC, 3 Hutton
Center, Santa Ana, California 92707, United States
| | - Daniel Weissbart
- MP Biomedicals SAS, Parc d’innovation-Rue Geiler de Kaysersberg, Illkirch-Graffenstaden 67402, France
| | - Hiromichi Nakahara
- Department
of Biophysical Chemistry, Nagasaki International University, Huis Ten
Bosch, Sasebo, Nagasaki 859-3298, Japan
| | - Osamu Shibata
- Department
of Biophysical Chemistry, Nagasaki International University, Huis Ten
Bosch, Sasebo, Nagasaki 859-3298, Japan
| | - Roger M. Leblanc
- Department
of Chemistry, University of Miami, 1301 Memorial Drive, Coral Gables, Florida 33146, United States
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22
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Kerketta R, Halász ÁM, Steinkamp MP, Wilson BS, Edwards JS. Effect of Spatial Inhomogeneities on the Membrane Surface on Receptor Dimerization and Signal Initiation. Front Cell Dev Biol 2016; 4:81. [PMID: 27570763 PMCID: PMC4981600 DOI: 10.3389/fcell.2016.00081] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2016] [Accepted: 07/25/2016] [Indexed: 11/23/2022] Open
Abstract
Important signal transduction pathways originate on the plasma membrane, where microdomains may transiently entrap diffusing receptors. This results in a non-random distribution of receptors even in the resting state, which can be visualized as “clusters” by high resolution imaging methods. Here, we explore how spatial in-homogeneities in the plasma membrane might influence the dimerization and phosphorylation status of ErbB2 and ErbB3, two receptor tyrosine kinases that preferentially heterodimerize and are often co-expressed in cancer. This theoretical study is based upon spatial stochastic simulations of the two-dimensional membrane landscape, where variables include differential distributions and overlap of transient confinement zones (“domains”) for the two receptor species. The in silico model is parameterized and validated using data from single particle tracking experiments. We report key differences in signaling output based on the degree of overlap between domains and the relative retention of receptors in such domains, expressed as escape probability. Results predict that a high overlap of domains, which favors transient co-confinement of both receptor species, will enhance the rate of hetero-interactions. Where domains do not overlap, simulations confirm expectations that homo-interactions are favored. Since ErbB3 is uniquely dependent on ErbB2 interactions for activation of its catalytic activity, variations in domain overlap or escape probability markedly alter the predicted patterns and time course of ErbB3 and ErbB2 phosphorylation. Taken together, these results implicate membrane domain organization as an important modulator of signal initiation, motivating the design of novel experimental approaches to measure these important parameters across a wider range of receptor systems.
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Affiliation(s)
- Romica Kerketta
- Department of Pathology, University of New Mexico Health Sciences Center Albuquerque, NM, USA
| | - Ádám M Halász
- Department of Mathematics and Mary Babb Randolph Cancer Center, West Virginia University Morgantown, WV, USA
| | - Mara P Steinkamp
- Department of Pathology, University of New Mexico Health Sciences CenterAlbuquerque, NM, USA; Cancer Center, University of New Mexico Health Sciences CenterAlbuquerque, NM, USA
| | - Bridget S Wilson
- Department of Pathology, University of New Mexico Health Sciences CenterAlbuquerque, NM, USA; Cancer Center, University of New Mexico Health Sciences CenterAlbuquerque, NM, USA
| | - Jeremy S Edwards
- Cancer Center, University of New Mexico Health Sciences CenterAlbuquerque, NM, USA; Department of Chemical and Biological Engineering, University of New MexicoAlbuquerque, NM, USA; Department of Chemistry and Chemical Biology, University of New MexicoAlbuquerque, NM, USA; Department of Molecular Genetics and Microbiology, University of New MexicoAlbuquerque, NM, USA
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23
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Sharma R, Roberts E. Gradient sensing by a bistable regulatory motif enhances signal amplification but decreases accuracy in individual cells. Phys Biol 2016; 13:036003. [DOI: 10.1088/1478-3975/13/3/036003] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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24
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Mlynarczyk PJ, Pullen RH, Abel SM. Confinement and diffusion modulate bistability and stochastic switching in a reaction network with positive feedback. J Chem Phys 2016; 144:015102. [DOI: 10.1063/1.4939219] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Paul J. Mlynarczyk
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Robert H. Pullen
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Steven M. Abel
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
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25
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Goodfellow HS, Frushicheva MP, Ji Q, Cheng DA, Kadlecek TA, Cantor AJ, Kuriyan J, Chakraborty AK, Salomon A, Weiss A. The catalytic activity of the kinase ZAP-70 mediates basal signaling and negative feedback of the T cell receptor pathway. Sci Signal 2015; 8:ra49. [PMID: 25990959 DOI: 10.1126/scisignal.2005596] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
T cell activation by antigens binding to the T cell receptor (TCR) must be properly regulated to ensure normal T cell development and effective immune responses to pathogens and transformed cells while avoiding autoimmunity. The Src family kinase Lck and the Syk family kinase ZAP-70 (ζ chain-associated protein kinase of 70 kD) are sequentially activated in response to TCR engagement and serve as critical components of the TCR signaling machinery that leads to T cell activation. We performed a mass spectrometry-based phosphoproteomic study comparing the quantitative differences in the temporal dynamics of phosphorylation in stimulated and unstimulated T cells with or without inhibition of ZAP-70 catalytic activity. The data indicated that the kinase activity of ZAP-70 stimulates negative feedback pathways that target Lck and thereby modulate the phosphorylation patterns of the immunoreceptor tyrosine-based activation motifs (ITAMs) of the CD3 and ζ chain components of the TCR and of signaling molecules downstream of Lck, including ZAP-70. We developed a computational model that provides a mechanistic explanation for the experimental findings on ITAM phosphorylation in wild-type cells, ZAP-70-deficient cells, and cells with inhibited ZAP-70 catalytic activity. This model incorporated negative feedback regulation of Lck activity by the kinase activity of ZAP-70 and predicted the order in which tyrosines in the ITAMs of TCR ζ chains must be phosphorylated to be consistent with the experimental data.
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Affiliation(s)
- Hanna Sjölin Goodfellow
- Howard Hughes Medical Institute, UCSF, San Francisco, CA 94143, USA.,Department of Medicine, UCSF, San Francisco, CA 94143, USA
| | - Maria P Frushicheva
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02142, USA
| | - Qinqin Ji
- Department of Chemistry, Brown University, Providence, RI 02912, USA
| | - Debra A Cheng
- Howard Hughes Medical Institute, UCSF, San Francisco, CA 94143, USA.,Department of Medicine, UCSF, San Francisco, CA 94143, USA
| | - Theresa A Kadlecek
- Howard Hughes Medical Institute, UCSF, San Francisco, CA 94143, USA.,Department of Medicine, UCSF, San Francisco, CA 94143, USA
| | - Aaron J Cantor
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.,California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA
| | - John Kuriyan
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.,California Institute for Quantitative Biosciences, University of California, Berkeley, CA 94720, USA.,Department of Chemistry, University of California, Berkeley, CA 94720, USA.,Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA.,Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Arup K Chakraborty
- Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02142, USA.,Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02142, USA.,Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02142, USA.,Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA 02142, USA.,Institute for Medical Engineering & Science, Massachusetts Institute of Technology, Cambridge, MA 02142, USA.,Ragon Institute of MGH, MIT, and Harvard, Cambridge, MA 02139, USA
| | - Arthur Salomon
- Department of Chemistry, Brown University, Providence, RI 02912, USA.,Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI 02912, USA
| | - Arthur Weiss
- Howard Hughes Medical Institute, UCSF, San Francisco, CA 94143, USA.,Department of Medicine, UCSF, San Francisco, CA 94143, USA
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26
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Chylek LA, Wilson BS, Hlavacek WS. Modeling biomolecular site dynamics in immunoreceptor signaling systems. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2015; 844:245-62. [PMID: 25480645 DOI: 10.1007/978-1-4939-2095-2_12] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The immune system plays a central role in human health. The activities of immune cells, whether defending an organism from disease or triggering a pathological condition such as autoimmunity, are driven by the molecular machinery of cellular signaling systems. Decades of experimentation have elucidated many of the biomolecules and interactions involved in immune signaling and regulation, and recently developed technologies have led to new types of quantitative, systems-level data. To integrate such information and develop nontrivial insights into the immune system, computational modeling is needed, and it is essential for modeling methods to keep pace with experimental advances. In this chapter, we focus on the dynamic, site-specific, and context-dependent nature of interactions in immunoreceptor signaling (i.e., the biomolecular site dynamics of immunoreceptor signaling), the challenges associated with capturing these details in computational models, and how these challenges have been met through use of rule-based modeling approaches.
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Affiliation(s)
- Lily A Chylek
- Department of Chemistry and Chemical Biology, Cornell University, 14853, Ithaca, NY, USA,
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27
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Nguyen PA, Field CM, Groen AC, Mitchison TJ, Loose M. Using supported bilayers to study the spatiotemporal organization of membrane-bound proteins. Methods Cell Biol 2015; 128:223-241. [PMID: 25997350 PMCID: PMC4578691 DOI: 10.1016/bs.mcb.2015.01.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Cell division in prokaryotes and eukaryotes is commonly initiated by the well-controlled binding of proteins to the cytoplasmic side of the cell membrane. However, a precise characterization of the spatiotemporal dynamics of membrane-bound proteins is often difficult to achieve in vivo. Here, we present protocols for the use of supported lipid bilayers to rebuild the cytokinetic machineries of cells with greatly different dimensions: the bacterium Escherichia coli and eggs of the vertebrate Xenopus laevis. Combined with total internal reflection fluorescence microscopy, these experimental setups allow for precise quantitative analyses of membrane-bound proteins. The protocols described to obtain glass-supported membranes from bacterial and vertebrate lipids can be used as starting points for other reconstitution experiments. We believe that similar biochemical assays will be instrumental to study the biochemistry and biophysics underlying a variety of complex cellular tasks, such as signaling, vesicle trafficking, and cell motility.
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Affiliation(s)
- Phuong A Nguyen
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
- Marine Biological Laboratory, Woods Hole, MA 02543, USA
| | - Christine M Field
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
- Marine Biological Laboratory, Woods Hole, MA 02543, USA
| | - Aaron C Groen
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
- Marine Biological Laboratory, Woods Hole, MA 02543, USA
| | - Timothy J Mitchison
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
- Marine Biological Laboratory, Woods Hole, MA 02543, USA
| | - Martin Loose
- Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA
- Institute of Science and Technology Austria, Am Campus 1, A-3400 Klosterneuburg, Austria
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28
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Cell-mimetic coatings for immune spheres. Colloids Surf B Biointerfaces 2014; 123:845-51. [PMID: 25454756 DOI: 10.1016/j.colsurfb.2014.10.029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2014] [Revised: 10/01/2014] [Accepted: 10/14/2014] [Indexed: 11/22/2022]
Abstract
Extrinsically induced or engineered cells are providing new therapeutic means in emerging fields such as cell therapeutics, immunomodulation and regenerative medicine. We are demonstrating a spatial induction method using lipid coatings, which can change signal presentation strength from material surface to adherent macrophage cells, that induce early cell-cell interaction leading to organotypic morphology. For that, we have developed a cell mimetic lipid coating with a rafts size to the order of transmembrane proteins (<10 nm) with enhanced lateral elastic properties. Such surface coatings are capable of reducing adherent macrophage spreading, while enabling early induction of cell-cell interaction to form organotypic macrophage colonies or "spheres" (M-spheres).
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29
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Abstract
Lipocalins are a class of proteins that scavenge hydrophobic molecules in diverse contexts, including the immune system, the nervous system, and cancer. A recent study by Watanbe et al. identifies lipocalin 2 produced by the female mouse reproductive tract as a sperm-capacitating agent that alters the membrane properties of sperm in preparation for fertilization. The potential for lipocalins to act as general modulators of plasma membrane bioactivity is discussed.
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Affiliation(s)
- Daniel Lingwood
- Ragon Institute of Massachusetts General Hospital, Massachusetts Institute of Technology, and Harvard University, 400 Technology Square, Cambridge, MA 02139, USA.
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30
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Avalos AM, Bilate AM, Witte MD, Tai AK, He J, Frushicheva MP, Thill PD, Meyer-Wentrup F, Theile CS, Chakraborty AK, Zhuang X, Ploegh HL. Monovalent engagement of the BCR activates ovalbumin-specific transnuclear B cells. ACTA ACUST UNITED AC 2014; 211:365-79. [PMID: 24493799 PMCID: PMC3920557 DOI: 10.1084/jem.20131603] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Monovalent engagement can trigger BCR signal transduction, and fine-tuning of BCR-ligand recognition can lead to B cell nonresponsiveness, activation, or inhibition. Valency requirements for B cell activation upon antigen encounter are poorly understood. OB1 transnuclear B cells express an IgG1 B cell receptor (BCR) specific for ovalbumin (OVA), the epitope of which can be mimicked using short synthetic peptides to allow antigen-specific engagement of the BCR. By altering length and valency of epitope-bearing synthetic peptides, we examined the properties of ligands required for optimal OB1 B cell activation. Monovalent engagement of the BCR with an epitope-bearing 17-mer synthetic peptide readily activated OB1 B cells. Dimers of the minimal peptide epitope oriented in an N to N configuration were more stimulatory than their C to C counterparts. Although shorter length correlated with less activation, a monomeric 8-mer peptide epitope behaved as a weak agonist that blocked responses to cell-bound peptide antigen, a blockade which could not be reversed by CD40 ligation. The 8-mer not only delivered a suboptimal signal, which blocked subsequent responses to OVA, anti-IgG, and anti-kappa, but also competed for binding with OVA. Our results show that fine-tuning of BCR-ligand recognition can lead to B cell nonresponsiveness, activation, or inhibition.
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Affiliation(s)
- Ana M Avalos
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142
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31
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Importance of crowding in signaling, genetic, and metabolic networks. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2014; 307:419-42. [PMID: 24380601 DOI: 10.1016/b978-0-12-800046-5.00012-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
It is now well established that the cell is a highly crowded environment. Yet, the effects of crowding on the dynamics of signaling pathways, gene regulation networks, and metabolic networks are still largely unknown. Crowding can alter both molecular diffusion and the equilibria of biomolecular reactions. In this chapter, we first discuss how diffusion can affect biochemical networks. Diffusion of transcription factors can increase noise in gene expression, while diffusion of proteins between intracellular compartments or between cells can reduce concentration fluctuations. In push-pull networks diffusion can impede information transmission, while in multisite protein modification networks diffusion can qualitatively change the macroscopic response of the system, such as the loss or emergence of bistability. Moreover, diffusion can directly change the metabolic flux. We describe how crowding affects diffusion, and thus how all these phenomena are influenced by crowding. Yet, a potentially more important effect of crowding on biochemical networks is mediated via the shift in the equilibria of bimolecular reactions, and we provide computational evidence that supports this idea. Finally, we discuss how the effects of crowding can be incorporated in models of biochemical networks.
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32
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Kochanczyk M, Jaruszewicz J, Lipniacki T. Stochastic transitions in a bistable reaction system on the membrane. J R Soc Interface 2013; 10:20130151. [PMID: 23635492 DOI: 10.1098/rsif.2013.0151] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Transitions between steady states of a multi-stable stochastic system in the perfectly mixed chemical reactor are possible only because of stochastic switching. In realistic cellular conditions, where diffusion is limited, transitions between steady states can also follow from the propagation of travelling waves. Here, we study the interplay between the two modes of transition for a prototype bistable system of kinase-phosphatase interactions on the plasma membrane. Within microscopic kinetic Monte Carlo simulations on the hexagonal lattice, we observed that for finite diffusion the behaviour of the spatially extended system differs qualitatively from the behaviour of the same system in the well-mixed regime. Even when a small isolated subcompartment remains mostly inactive, the chemical travelling wave may propagate, leading to the activation of a larger compartment. The activating wave can be induced after a small subdomain is activated as a result of a stochastic fluctuation. Such a spontaneous onset of activity is radically more probable in subdomains characterized by slower diffusion. Our results show that a local immobilization of substrates can lead to the global activation of membrane proteins by the mechanism that involves stochastic fluctuations followed by the propagation of a semi-deterministic travelling wave.
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Affiliation(s)
- Marek Kochanczyk
- Institute of Fundamental Technological Research, Polish Academy of Sciences, Warsaw, Poland
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Mukherjee S, Zhu J, Zikherman J, Parameswaran R, Kadlecek TA, Wang Q, Au-Yeung B, Ploegh H, Kuriyan J, Das J, Weiss A. Monovalent and multivalent ligation of the B cell receptor exhibit differential dependence upon Syk and Src family kinases. Sci Signal 2013; 6:ra1. [PMID: 23281368 DOI: 10.1126/scisignal.2003220] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The Src and Syk families of kinases are two distinct sets of kinases that play critical roles in initiating membrane-proximal B cell receptor (BCR) signaling. However, unlike in other lymphocytes, such as T cells, the "division of labor" between Src family kinases (SFKs) and Syk in B cells is not well separated because both Syk and SFKs can phosphorylate immunoreceptor tyrosine-based activation motifs (ITAMs) present in proteins comprising the BCR. To understand why B cells require both SFKs and Syk for activation, we investigated the roles of both families of kinases in BCR signaling with computational modeling and in vitro experiments. Our computational model suggested that positive feedback enabled Syk to substantially compensate for the absence of SFKs when spatial clustering of BCRs was induced by multimeric ligands. We confirmed this prediction experimentally. In contrast, when B cells were stimulated by monomeric ligands that failed to produce BCR clustering, both Syk and SFKs were required for complete and rapid BCR activation. Our data suggest that SFKs could play a pivotal role in increasing BCR sensitivity to monomeric antigens of pathogens and in mediating a rapid response to soluble multimeric antigens of pathogens that can induce spatial BCR clustering.
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Affiliation(s)
- Sayak Mukherjee
- Battelle Center for Mathematical Medicine, The Research Institute at Nationwide Children's Hospital, Department of Pediatrics, The Ohio State University, Columbus, OH 43205, USA
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