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Abraham G, Chaderjian A, Nguyen A, Wilken S, Saleh OA. Nucleic acid liquids. Rep Prog Phys 2024. [PMID: 38697088 DOI: 10.1088/1361-6633/ad4662] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2024]
Abstract
The confluence of recent discoveries of the roles of biomolecular liquids in living systems and modern abilities to precisely synthesize and modify nucleic acids (NAs) has led to a surge of interest in liquid phases of NAs. These phases can be formed primarily from NAs, as driven by basepairing interactions, or from the electrostatic combination (coacervation) of negatively charged NAs and positively charged molecules. Generally, the use of sequence-engineered NAs provides the means to tune microsopic particle properties, and thus imbue specific, customizable behaviors into the resulting liquids. In this way, researchers have used NA liquids to tackle fundamental problems in the physics of finite valence soft materials, and to create liquids with novel structured and/or multi-functional properties. Here, we review this growing field, discussing the theoretical background of NA liquid phase separation, quantitative understanding of liquid material properties, and the broad and growing array of functional demonstrations in these materials. We close with a few comments discussing remaining open questions and challenges in the field.
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Affiliation(s)
- Gabrielle Abraham
- University of California Santa Barbara, BioEngineering Building, Rm 1206, Santa Barbara, California, 93106, UNITED STATES
| | - Aria Chaderjian
- University of California Santa Barbara, Physics Department, Santa Barbara, California, 93106, UNITED STATES
| | - Anna Nguyen
- University of California Santa Barbara, BMSE Program, Santa Barbara, California, 93106, UNITED STATES
| | - Sam Wilken
- University of California Santa Barbara, Bioengineering Building, Santa Barbara, California, 93106, UNITED STATES
| | - Omar A Saleh
- Department of Materials and Physics, University of California Santa Barbara, Bldg 503 Rm 1355, Engineering II, Santa Barbara, Santa Barbara, California, 93106, UNITED STATES
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2
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Gao D, Wilken S, Nguyen ABN, Abraham GR, Liedl T, Saleh OA. Controlling the size and adhesion of DNA droplets using surface- enriched DNA molecules. Soft Matter 2024; 20:1275-1281. [PMID: 38236226 DOI: 10.1039/d3sm01264f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2024]
Abstract
Liquid droplets of biomolecules serve as organizers of the cellular interior and are of interest in biosensing and biomaterials applications. Here, we investigate means to tune the interfacial properties of a model biomolecular liquid consisting of multi-armed DNA 'nanostar' particles. We find that long DNA molecules that have binding affinity for the nanostars are preferentially enriched on the interface of nanostar droplets, thus acting as surfactants. Fluorescent measurements indicate that, in certain conditions, the interfacial density of the surfactant is around 20 per square micron, indicative of a sparse brush-like structure of the long, polymeric DNA. Increasing surfactant concentration leads to decreased droplet size, down to the sub-micron scale, consistent with droplet coalesence being impeded by the disjoining pressure created by the brush-like surfactant layer. Added DNA surfactant also keeps droplets from adhering to both hydrophobic and hydrophilic solid surfaces, apparently due to this same disjoining effect of the surfactant layer. We thus demonstrate control of the size and adhesive properties of droplets of a biomolecular liquid, with implications for basic biophysical understanding of such droplets, as well as for their applied use.
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Affiliation(s)
- Daqian Gao
- Physics Department, University of California, Santa Barbara, California 93106, USA
| | - Sam Wilken
- Physics Department, University of California, Santa Barbara, California 93106, USA
- Materials Department, University of California, Santa Barbara, California 93106, USA.
| | - Anna B N Nguyen
- Biomolecular Science & Engineering Program, University of California, Santa Barbara, California 93106, USA
| | - Gabrielle R Abraham
- Physics Department, University of California, Santa Barbara, California 93106, USA
| | - Tim Liedl
- Department für Physik, Ludwig-Maximilians-Universität, München 80539, Germany
| | - Omar A Saleh
- Physics Department, University of California, Santa Barbara, California 93106, USA
- Biomolecular Science & Engineering Program, University of California, Santa Barbara, California 93106, USA
- Materials Department, University of California, Santa Barbara, California 93106, USA.
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Wilken S, Guo AZ, Levine D, Chaikin PM. Dynamical Approach to the Jamming Problem. Phys Rev Lett 2023; 131:238202. [PMID: 38134769 DOI: 10.1103/physrevlett.131.238202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Accepted: 10/12/2023] [Indexed: 12/24/2023]
Abstract
A simple dynamical model, biased random organization (BRO), appears to produce configurations known as random close packing (RCP) as BRO's densest critical point in dimension d=3. We conjecture that BRO likewise produces RCP in any dimension; if so, then RCP does not exist in d=1-2 (where BRO dynamics lead to crystalline order). In d=3-5, BRO produces isostatic configurations and previously estimated RCP volume fractions 0.64, 0.46, and 0.30, respectively. For all investigated dimensions (d=2-5), we find that BRO belongs to the Manna universality class of dynamical phase transitions by measuring critical exponents associated with the steady-state activity and the long-range density fluctuations. Additionally, BRO's distribution of near contacts (gaps) displays behavior consistent with the infinite-dimensional theoretical treatment of RCP when d≥4. The association of BRO's densest critical configurations with random close packing implies that RCP's upper-critical dimension is consistent with the Manna class d_{uc}=4.
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Affiliation(s)
- Sam Wilken
- Materials Department, University of California, Santa Barbara, California 93106, USA
| | - Ashley Z Guo
- Department of Chemical and Biochemical Engineering, Rutgers University-New Brunswick, Piscataway, New Jersey 08854, USA
| | - Dov Levine
- Department of Physics, Technion-IIT, Haifa 32000, Israel
| | - Paul M Chaikin
- Department of Chemical and Biochemical Engineering, Rutgers University-New Brunswick, Piscataway, New Jersey 08854, USA
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Saleh OA, Wilken S, Squires TM, Liedl T. Vacuole dynamics and popping-based motility in liquid droplets of DNA. Nat Commun 2023; 14:3574. [PMID: 37328453 PMCID: PMC10275875 DOI: 10.1038/s41467-023-39175-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2022] [Accepted: 06/01/2023] [Indexed: 06/18/2023] Open
Abstract
Liquid droplets of biomolecules play key roles in organizing cellular behavior, and are also technologically relevant, yet physical studies of dynamic processes of such droplets have generally been lacking. Here, we investigate and quantify the dynamics of formation of dilute internal inclusions, i.e., vacuoles, within a model system consisting of liquid droplets of DNA 'nanostar' particles. When acted upon by DNA-cleaving restriction enzymes, these DNA droplets exhibit cycles of appearance, growth, and bursting of internal vacuoles. Analysis of vacuole growth shows their radius increases linearly in time. Further, vacuoles pop upon reaching the droplet interface, leading to droplet motion driven by the osmotic pressure of restriction fragments captured in the vacuole. We develop a model that accounts for the linear nature of vacuole growth, and the pressures associated with motility, by describing the dynamics of diffusing restriction fragments. The results illustrate the complex non-equilibrium dynamics possible in biomolecular condensates.
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Affiliation(s)
- Omar A Saleh
- Materials Department and Physics Department, University of California, Santa Barbara, CA, 93106, USA.
| | - Sam Wilken
- Materials Department and Physics Department, University of California, Santa Barbara, CA, 93106, USA
| | - Todd M Squires
- Chemical Engineering Department, University of California, Santa Barbara, CA, 93106, USA
| | - Tim Liedl
- Physics Department, Ludwig-Maximilians University, Munich, Germany
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Wilken S, Guerra RE, Levine D, Chaikin PM. Random Close Packing as a Dynamical Phase Transition. Phys Rev Lett 2021; 127:038002. [PMID: 34328779 DOI: 10.1103/physrevlett.127.038002] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Revised: 03/31/2021] [Accepted: 04/23/2021] [Indexed: 06/13/2023]
Abstract
Sphere packing is an ancient problem. The densest packing is known to be a face-centered cubic (FCC) crystal, with space-filling fraction ϕ_{FCC}=π/sqrt[18]≈0.74. The densest "random packing," random close packing (RCP), is yet ill defined, although many experiments and simulations agree on a value ϕ_{RCP}≈0.64. We introduce a simple absorbing-state model, biased random organization (BRO), which exhibits a Manna class dynamical phase transition between absorbing and active states that has as its densest critical point ϕ_{c_{max}}≈0.64≈ϕ_{RCP} and, like other Manna class models, is hyperuniform at criticality. The configurations we obtain from BRO appear to be structurally identical to RCP configurations from other protocols. This leads us to conjecture that the highest-density absorbing state for an isotropic biased random organization model produces an ensemble of configurations that characterizes the state conventionally known as RCP.
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Affiliation(s)
- Sam Wilken
- Physics Department, New York University, 726 Broadway, New York, New York 10003, USA
| | - Rodrigo E Guerra
- Physics Department, New York University, 726 Broadway, New York, New York 10003, USA
| | - Dov Levine
- Department of Physics, Technion, IIT, 32000 Haifa, Israel
| | - Paul M Chaikin
- Physics Department, New York University, 726 Broadway, New York, New York 10003, USA
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Wilken S, Guerra RE, Pine DJ, Chaikin PM. Hyperuniform Structures Formed by Shearing Colloidal Suspensions. Phys Rev Lett 2020; 125:148001. [PMID: 33064537 DOI: 10.1103/physrevlett.125.148001] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Revised: 05/21/2020] [Accepted: 07/01/2020] [Indexed: 06/11/2023]
Abstract
In periodically sheared suspensions there is a dynamical phase transition, characterized by a critical strain amplitude γ_{c}, between an absorbing state where particle trajectories are reversible and an active state where trajectories are chaotic and diffusive. Repulsive nonhydrodynamic interactions between "colliding" particles' surfaces have been proposed as a source of this broken time reversal symmetry. A simple toy model called random organization qualitatively reproduces the dynamical features of this transition. Random organization and other absorbing state models exhibit hyperuniformity, a strong suppression of density fluctuations on long length scales quantified by a structure factor S(q→0)∼q^{α} with α>0, at criticality. Here we show experimentally that the particles in periodically sheared suspensions organize into structures with anisotropic short-range order but isotropic, long-range hyperuniform order when oscillatory shear amplitudes approach γ_{c}.
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Affiliation(s)
- Sam Wilken
- Center for Soft Matter Research, Department of Physics, New York University, New York 10003, USA
| | - Rodrigo E Guerra
- Center for Soft Matter Research, Department of Physics, New York University, New York 10003, USA
| | - David J Pine
- Center for Soft Matter Research, Department of Physics, New York University, New York 10003, USA
| | - Paul M Chaikin
- Center for Soft Matter Research, Department of Physics, New York University, New York 10003, USA
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Wilken S, Miskin MZ, Jaeger HM. Optimizing a reconfigurable material via evolutionary computation. Phys Rev E Stat Nonlin Soft Matter Phys 2015; 92:022212. [PMID: 26382399 DOI: 10.1103/physreve.92.022212] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Indexed: 06/05/2023]
Abstract
Rapid prototyping by combining evolutionary computation with simulations is becoming a powerful tool for solving complex design problems in materials science. This method of optimization operates in a virtual design space that simulates potential material behaviors and after completion needs to be validated by experiment. However, in principle an evolutionary optimizer can also operate on an actual physical structure or laboratory experiment directly, provided the relevant material parameters can be accessed by the optimizer and information about the material's performance can be updated by direct measurements. Here we provide a proof of concept of such direct, physical optimization by showing how a reconfigurable, highly nonlinear material can be tuned to respond to impact. We report on an entirely computer controlled laboratory experiment in which a 6×6 grid of electromagnets creates a magnetic field pattern that tunes the local rigidity of a concentrated suspension of ferrofluid and iron filings. A genetic algorithm is implemented and tasked to find field patterns that minimize the force transmitted through the suspension. Searching within a space of roughly 10^{10} possible configurations, after testing only 1500 independent trials the algorithm identifies an optimized configuration of layered rigid and compliant regions.
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Affiliation(s)
- Sam Wilken
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Marc Z Miskin
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Heinrich M Jaeger
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
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Worden AZ, Follows MJ, Giovannoni SJ, Wilken S, Zimmerman AE, Keeling PJ. Rethinking the marine carbon cycle: Factoring in the multifarious lifestyles of microbes. Science 2015; 347:1257594. [DOI: 10.1126/science.1257594] [Citation(s) in RCA: 439] [Impact Index Per Article: 48.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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Lubbers LA, Xu Q, Wilken S, Zhang WW, Jaeger HM. Dense suspension splat: monolayer spreading and hole formation after impact. Phys Rev Lett 2014; 113:044502. [PMID: 25105622 DOI: 10.1103/physrevlett.113.044502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Indexed: 06/03/2023]
Abstract
We use experiments and minimal numerical models to investigate the rapidly expanding monolayer formed by the impact of a dense suspension drop against a smooth solid surface. The expansion creates a lacelike pattern of particle clusters separated by particle-free regions. Both the expansion and the development of the spatial inhomogeneity are dominated by particle inertia and, therefore, are robust and insensitive to details of the surface wetting, capillarity, and viscous drag.
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Affiliation(s)
- Luuk A Lubbers
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA and Physics of Fluids Group, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands
| | - Qin Xu
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Sam Wilken
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Wendy W Zhang
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
| | - Heinrich M Jaeger
- James Franck Institute and Department of Physics, The University of Chicago, Chicago, Illinois 60637, USA
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Abstract
In the field of fluid mechanics, many dynamical processes not only occur over a very short time interval but also require high spatial resolution for detailed observation, scenarios that make it challenging to observe with conventional imaging systems. One of these is the drop impact of liquids, which usually happens within one tenth of millisecond. To tackle this challenge, a fast imaging technique is introduced that combines a high-speed camera (capable of up to one million frames per second) with a macro lens with long working distance to bring the spatial resolution of the image down to 10 µm/pixel. The imaging technique enables precise measurement of relevant fluid dynamic quantities, such as the flow field, the spreading distance and the splashing speed, from analysis of the recorded video. To demonstrate the capabilities of this visualization system, the impact dynamics when droplets of non-Newtonian fluids impinge on a flat hard surface are characterized. Two situations are considered: for oxidized liquid metal droplets we focus on the spreading behavior, and for densely packed suspensions we determine the onset of splashing. More generally, the combination of high temporal and spatial imaging resolution introduced here offers advantages for studying fast dynamics across a wide range of microscale phenomena.
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Affiliation(s)
- Qin Xu
- Department of Physics, The University of Chicago; James Franck Institute, The University of Chicago
| | - Ivo Peters
- James Franck Institute, The University of Chicago
| | - Sam Wilken
- Department of Physics, The University of Chicago; James Franck Institute, The University of Chicago
| | - Eric Brown
- Department of Mechanical Engineering and Materials Science, Yale University
| | - Heinrich Jaeger
- Department of Physics, The University of Chicago; James Franck Institute, The University of Chicago;
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Brück S, Krause C, Turrisi R, Beverina L, Wilken S, Saak W, Lützen A, Borchert H, Schiek M, Parisi J. Structure-property relationship of anilino-squaraines in organic solar cells. Phys Chem Chem Phys 2013; 16:1067-77. [PMID: 24288034 DOI: 10.1039/c3cp54163k] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Soluble molecular semiconductors are a promising alternative to semiconducting polymers in the field of organic photovoltaics. Here, three custom-made symmetric 1,3-bis(N,N-alkylated-2,6-dihydroxy-anilino)squaraines containing systematic variations in their molecular structures are compared regarding their applicability as donor materials in bulk-heterojunction solar cells. The terminal substitution pattern of the squaraines is varied from cyclic over linear to branched including a stereogenic center. Single crystal structures are determined, and, in the case of chiral squaraine, unusual formation of stereoisomer co-crystals is revealed. The thin film absorbance spectra show characteristic signatures of H- and J-bands or hint at the formation of tautomers. The general feasibility of these model compounds for photovoltaic applications is studied by light-induced electron spin resonance spectroscopy. The impact of the different molecular substitution patterns on aggregation behavior and, consequently, their optoelectronic solid state properties including charge carrier mobility and finally the solar cell performance are investigated.
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Affiliation(s)
- S Brück
- Institute of Physics, Energy and Semiconductor Research Laboratory, Carl von Ossietzky University of Oldenburg, D-26111 Oldenburg, Germany.
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Dieckmann KP, Wilken S, Loy V, Matthies C, Kleinschmidt K, Bedke J, Martinschek A, Souchon R, Pichlmeier U, Kliesch S. Treatment of testicular intraepithelial neoplasia (intratubular germ cell neoplasia unspecified) with local radiotherapy or with platinum-based chemotherapy: a survey of the German Testicular Cancer Study Group. Ann Oncol 2013; 24:1332-7. [PMID: 23293116 DOI: 10.1093/annonc/mds628] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
BACKGROUND The treatment of testicular intraepithelial neoplasia (TIN), the progenitor of testicular germ cell tumours (GCTs), is based on little data. PATIENTS AND METHODS Two hundred and twenty-eight GCT patients with contralateral TIN were retrospectively enrolled. Ten had surveillance, 122 radiotherapy to testis with 18-20 Gy, 30 cisplatin-based chemotherapy (two cycles), 51 chemotherapy (three cycles), and 15 carboplatin. The study end point was a malignant event (ME), defined as detection of TIN upon control biopsy or occurrence of a second GCT. The Secondary end point was hypogonadism during follow-up. RESULTS Numbers, proportions of ME, and median event-free survival (EFS) times were: radiotherapy N = 3, 2.5%, 11.08 years; chemotherapy (two cycles) N = 15, 50%, 3.0 years; chemotherapy (three cycles) N = 12, 23.5%, 9.83 years; carboplatin N = 10, 66%, 0.9 years; surveillance N = 5, 50%, 7.08 years. EFS is significantly different among the groups. Hypogonadism rates were in radiotherapy patients 30.8%, chemotherapy (two cycles) 13%, chemotherapy (three cycles) 17.8%, carboplatin 40%, surveillance 40%. CONCLUSIONS Local radiotherapy is highly efficacious in curing TIN. Chemotherapy is significantly less effective and the cure rates are dose-dependent. Though hypogonadism occurs in one-third of patients, radiotherapy with 20 Gy remains the standard management of TIN.
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Affiliation(s)
- K-P Dieckmann
- Department of Urology, Albertinen-Krankenhaus, Hamburg, Germany.
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Wilken S, Schmees G, Schneider E. A putative helical domain in the MalK subunit of the ATP-binding-cassette transport system for maltose of Salmonella typhimurium (MalFGK2) is crucial for interaction with MalF and MalG. A study using the LacK protein of Agrobacterium radiobacter as a tool. Mol Microbiol 1996; 22:655-66. [PMID: 8951813 DOI: 10.1046/j.1365-2958.1996.d01-1724.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The ATP-binding-cassette (ABC) protein LacK of Agrobacterium radiobacter displays high sequence similarity to the MalK subunit of the Salmonella typhimurium maltose-transport system (MalFGK2). We have used LacK as a tool to identify sites of interaction of MalK with the membrane-integral components MalF and MalG. Small amounts of LacK, resulting from the expression of the plasmid-borne lacK gene, proved to be sufficient for partial restoration of growth of a malK strain of S. typhimurium on maltose. LacK failed to substitute for MalK in regulating the expression of maltose-inducible genes but the hybrid complex MalFGLacK2 was sensitive to inducer exclusion. The lacK gene also complemented a ugpC mutant of Escherichia coli to growth on sn-glycerol-3-phosphate as the phosphate source. Partially purified LacK exhibited a spontaneous ATPase activity comparable to that of MalK. A MalK"-'LacK chimeric protein was isolated (by in vivo recombination) in which the N-terminal 140 amino acids of MalK are fused to residues 141-363 of LacK. The protein substituted for MalK in maltose transport considerably better than LacK. Furthermore, random mutagenesis of the plasmid-borne lacK gene yielded three clones that were superior to wild-type lacK in complementing a malK mutation. Single mutations (V114M or L123F) substantially improved the growth of a malK strain on maltose, whereas a double mutation (L123F, S295N) resulted in growth and transport rates that were indistinguishable from those obtained with MalK. In contrast, the introduction of the single change S295N into LacK had no effect but combination with the V114M mutation led to a further twofold increase in transport activity. These results indicate that a putative helical domain in MalK, encompassing residues 89-140, is crucial for a functional, high-affinity interaction with MalF and MalG.
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Affiliation(s)
- S Wilken
- Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, Germany
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Schneider E, Wilken S, Schmid R. Nucleotide-induced conformational changes of MalK, a bacterial ATP binding cassette transporter protein. J Biol Chem 1994; 269:20456-61. [PMID: 8051143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Nucleotide-induced structural rearrangements of MalK, the ATP-hydrolyzing component of the ATP binding cassette transporter for maltose from Salmonella typhimurium were investigated by means of analysis of intrinsic tryptophan fluorescence and limited proteolysis. ATP was found to decrease the tryptophan fluorescence of purified MalK by 37 +/- 1%. ADP or adenosine 5'-O-(3-(thio)triphosphate) (ATP gamma S) caused similar quenching while AMP was rather ineffective. Mg2+ ions were not required. Exposure of MalK to increasing concentrations of trypsin and subsequent analysis by SDS-polyacrylamide gel electrophoresis and immunoblotting revealed the formation of three major transiently stable peptide fragments of 24 (T2), 23 (T3), and 20 kDa (T4), respectively. In addition, a minor rapidly degraded fragment of 33 kDa (T1) was observed. However, in the presence of MgATP, fragment T1 as well as a substantial fraction of native MalK were strongly protected against proteolytic attack. Similar protection against the protease was observed in the presence of MgGTP or, to a lesser extent, MgCTP. In contrast, MgADP, ATP in the presence of EDTA, CaATP or nonhydrolyzable nucleotides such as MgATP gamma S or MgAMP-PNP (beta, gamma-imidoadenosine-5'-triphosphate) failed to significantly affect the susceptibility of MalK to the protease. MgATP similarly affected the tryptic digestion pattern of a mutant protein (MalKK42R) that exhibits only a much reduced ATPase activity but has retained the capability to bind nucleotides. N-terminal protein sequence analysis of the peptides revealed cleavage by trypsin at Arg66 (T1), Arg146 (T2), Arg153 (T3), and Arg185 (T4), respectively. These results indicate that (i) nucleotide binding to MalK is accompanied by a global conformational change of the protein; (ii) a very specific interaction occurs with substrates of the MalK-ATPase, resulting in structural changes that involve the helical domain from Arg66 to Arg146; and (iii) the C-terminal half of MalK is rather resistant to proteolysis.
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Affiliation(s)
- E Schneider
- Arbeitsgruppe Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, Federal Republic of Germany
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15
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Schneider E, Wilken S, Schmid R. Nucleotide-induced conformational changes of MalK, a bacterial ATP binding cassette transporter protein. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)32014-8] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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16
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Walter C, Wilken S, Schneider E. Characterization of site-directed mutations in conserved domains of MalK, a bacterial member of the ATP-binding cassette (ABC) family [corrected]. FEBS Lett 1992; 303:41-4. [PMID: 1592114 DOI: 10.1016/0014-5793(92)80473-t] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Site-directed mutagenesis was used to change four amino acid residues (Q82, P152, L179, H192) in the MalK subunit of S. typhimurium maltose transport system which are highly conserved among members of the ATP-binding cassette (ABC) family. Replacement of H192 caused complete failure to complement the transport defect of a malK strain whereas changes of the other residues resulted in reduced or wild-type activity. The purified mutant proteins exhibited ATPase activity comparable to wild-type MalK.
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Affiliation(s)
- C Walter
- Universität Osnabrück, FB Biologie/Chemie, Germany
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