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International Conference onNanobiology 2001Program |
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Thursday, October 25, 2001 3:00
PM Registration in the upper lobby of the Emory Conference Center Hotel 6:00
PM - 7:15 PM DINNER
(Dinning Room) Chair: Peter Hänggi, University of Augsburg 7:15 PM -7:30 PM WELCOMING ADDRESS AND OPENING REMARKS, Raymond C. DuVarney, Chair, Department of Physics, Emory University (Oak Amphitheater) 7:30
PM - 8:10 PM BROWNIAN MOTORS AND
PUMPS: THE CONSTRUCTIVE ROLE OF NOISE IN NANOMOLECULAR MACHINES, R.
Dean Astumian (Dean.Astumian@umit.maine.edu) University of Maine, Department of
Physics, Orono, ME 04473 Machines operating at the microscopic level are subject to random effects due to thermal noise. I will discuss how molecular pumps and motors can exploit the thermal noise to efficiently harness chemical energy to drive directed transport and exert force by a mechanism similar to that of a solid state adiabatic electron pump. 8:10
PM - 8:50 PM MODELING TRANSPORT BY
MOLECULAR MOTORS AND THEIR ROLE IN CELLULAR MITOSIS, Jorge V. José
(jjv@neu.edu)
Phys. Dept. Northeastern University,
360 Huntingon Avenue, Boston, MA 02115 My talk will deal with two problems. (i) The molecular motor motility-assays and (ii) the self-organized formation of bipolar spindles in in vitro experiments. (i) A two-dimensional stochastic model for the dynamics of microtubules in gliding-assay experiments is presented here which includes the viscous drag acting on the moving fiber and the interaction with the kinesins. We model the kinesin as a spring, and explicitly use parameter values to characterize the model from experimental data. We numerically compute the mean attachment lifetimes of all motors, the total force exerted on the microtubules at all times, the effects of a distribution in the motor speeds, and also the mean velocity of a microtubule in a gliding assay. We find quantitative agreement with the results of Howard et al..Nature, 342:154-158 (1989.) (ii) It had been assumed that the formation of the mitotic spindle during cell division depends essentially on the presence of chromosomes and centrosomes. In vitro experiments (Heald et al. Nature,382, 420 (1996)) have shown, however, that bipolar spindles can form around DNA-coated beads. It was suggested that motor proteins (MP) induce the self-organization of the microtubules (MT). Here I will present a simple model that attempts to describe these experiments using kinesin and dyenin motors to produce spindle-like structures. I will discuss the different types of dynamic structures that can form as a function of the ratios of the two types of molecular motors. Friday, October 26, 2001 Chair: Anatoly B.
Kolomeisky, Rice University 9:00
AM - 9:40 AM DRUNKEN MOLECULAR MOTORS,
Jacques Prost (jacques.prost@curie.fr) Institut Curie, 11 rue Pierre et Marie
Curie, Laboratoire Physico-Chimie Curie UMR CNRS 168 , Paris, 75231, France Recently a mutant of NCD from the Kinesin family has been shown to undergo in the presence of ATP an essentially diffusive behavior at a single molecule level, and bidirectional behavior when in large collections [1]. We show that the concept of dynamical transition provides a natural framework for understanding these unusual features, and compare them to the actin-myosin case. Eventually we describe a new experiment designed to probe the behavior of molecular motors over a wide range of timescale. [1] Endow and Higuchi, Nature 406, 913 (2000) In collaboration with M. Badoual, G. Cappello, F. Julicher Section de recherche, 26 rue d'Ulm, 75248 PARIS Cédex 05, France 9:40
AM - 10:20 AM DOES KINESIN STEP
BETWEEN NEIGHBOURING PROTOFILAMENTS?, Nick James Carter (N.Carter@mcri.ac.uk) Marie
Curie Research Institute, The Chart, Oxted, Surrey, RH8 0TL, England Advances in instrumentation, particularly during the last decade, have enabled mechanical measurements from single motor molecules. Such recordings require force measurements of the order of a piconewton (10-12 N) and movements of the order of a nanometre (10-9 m). A highly stable single beam optical trap with a sufficiently accurate position transducer is suitable for this level of measurement. The motor molecule is attached to a bead (sub-micrometer diameter) and it's corresponding track to the microscope slide. The bead is trapped in the laser beam and used as a handle to bring the motor and track together. Many laboratories have successfully recorded forces and steps from several different motors of the myosin and kinesin families using this technique. Molecular motors of the kinesin family transport organelles along the microtubule cytoskeleton in all plant and animal cells. Kinesin is a dimer with two identical motor domains (or heads). Each head contains binding sites for the microtubule track and for ATP. The hydrolysis of ATP provides the energy to perform work as the kinesin steps along the microtubule. Unlike many of its relatives, kinesin is mechanically processive, meaning that a single molecule can take multiple steps along the microtubule before detaching. Microtubules are cylindrical bundles of protofilaments. Each protofilament consists of a string of kinesin binding sites on an 8nm axial repeat. It is known that kinesin walks parallel to the protofilament axis (Ray et al, J.Cell.Biol. 121:1083) with 8nm steps. However it is not known whether kinesin straddles between neighbouring protofilaments or follows a single protofilament. Averaging of alternate steps from single molecule records provides reduced noise records for each head in the kinesin dimer, without reducing bandwidth. Preliminary results suggest that kinesin follows a single protofilament, and does not step between adjacent protofilaments. In collaboration with Barry Grant & Rob Cross. 10:20
AM - 10:40 AM BREAK Chair: Michael F.
Shlesinger, Office of Naval Research 10:40
AM - 10:50 AM INFORMATION ON HOW TO
OBTIAN VENTURE CAPITAL FOR NEW BIOTECHNOLOGY, Brian Leslie (bleslie@mmmlaw.com
) and John Yates, Biotech, Corporate,
& Technology Groups, Morris, Manning & Martin LLP, Atlanta 10:50
AM - 11:30 AM FORCE PRODUCTION BY
INDIVIDUAL KINESIN MOLECULES, Koen Visscher (visscher@physics.arizona.edu)
Department of Physics, University of Arizona,
1118 E. 4th Street, Tucson, AZ 85701 Kinesin motors convert chemical energy stored in ATP into mechanical work through a reaction cycle that couples nucleotide hydrolysis to directed motion along microtubules. To shed light on this coupling mechanism we measured velocities of individual kinesin molecules at varying ATP concentrations and loads using a feedback-driven optical trap which maintains a precise and controlled external load on an individual kinesin molecule. These experiments revealed the load-dependent kinetic rates in the cycle, which are of interest because they identify transitions where structural changes are likely to occur. Subsequent modeling of the velocity data indicates that a thermally-activated and load-dependent isomerization directly follows ATP binding and occurs before hydrolysis. This model quantitatively accounts for velocity data over a wide range of loads and ATP concentrations, and further indicates that movement may be accomplished through two sequential, non- identical, 4-nm sized substeps. 11:30
AM - 12:10 AM DESCRIBING THE DYNAMICS
OF KINESIN AND MYOSIN V, Michael E. Fisher (claremon@ipst.umd.edu)
Institute for Physical Science and
Tech., University of Maryland, College Park, Maryland 20742-2431 Kinesin and Myosin V are processive motor proteins that transport cellular cargoes along linear polymeric tracks consuming one molecule of ATP per discrete step of size d = 8.2 nm and ~36 nm, along microtubules and actin filaments, respectively. The statistics of individual motor molecules have been studied in vitro to determine the mean velocity, V, the dispersion, D, and mean run length, L, under varying imposed load forces, F, and ATP concentration, etc. [1-5]. To describe the mechanochemistry of the dynamics, explicit, exact results have been developed for V, D, etc., for N-state periodic sequential stochastic models that (i) include the distribution of the load, F, over the various forward and backward rate processes [6,7]; (ii) allow for "deaths" or irreversible detatchments from the track; (iii) encompass branching and parallel processes [8,9]; and (iv) can represent arbitrary waiting-time distributions [10] which may be effectively summarized by the "mechanicity" of the specific process: M = 0 for Poissonian kinetics, M = 1 for a clockwork transition [7,10]. The crucial "load distribution factors" identify substep displacements along the track and associated dwell times. Analysis [7] of the extensive kinesin data [1,2] demonstrates that the simplest (N=2)-state model provides a quantitatively good description of the (V, F, L, [ATP]) interdependence and matches the relative acceleration previously observed [11] under assisting loads (F < 0). The dispersion, D, or “randomness” r = 2D/dV , requires a mechanicity, M = 0.6 for hydrolysis (after ATP-binding) or an (N=4)-state kinetic (M=0) model. An initial substep around 2 nm is predicted; an intermediate step level around d = 4.5 nm, is allowed by the N=4 fits and is in speculative concordance with recent experiments [12]. An N=2 model also describes successfully all current data [3-5] on the load- and [ATP]-dependence of the overall dwell time, and on stall forces and reverse steps of Myosin V [13]. Predictions include a substep of 14-15 nm on binding ATP, in accord with observed “half-steps,” and the variation of randomness under assisting and resisting loads [13]. [1] K. Visscher, M.J. Schnitzer and S.M. Block, Nature 400 (1999) 184-189. [2] M.J. Schnitzer et al., Nature Cell Biol. 2 (2000) 718-723. [3] A.D. Mehta et al., Nature 400 (1999) 590-593. [4] M. Rief et al., PNAS 97 (2000) 9482-86. [5] A. Mehta, J. Cell. Sci. 114 (2001) 1981-98. [6] M.E. Fisher and A.B. Kolomeisky, PNAS 96 (1999) 6597-6602; Physica A 274 (1999) 241-266. [7] M.E. Fisher and A.B. Kolomeisky, PNAS 98 (2001) 7748-53. [8] A.B. Kolomeisky and M.E. Fisher, Physica A 279 (2000) 1-20. [9] A.B. Kolomeisky (2001) to be published. [10] A.B. Kolomeisky and M.E. Fisher, J. Chem. Phys. 113 (2000) 10867-77. [11] C.M. Coppin et al., PNAS 94 (1997) 8539-44. [12] M. Nishiyama et al., Nature Cell Biol. 3 (2001) 425-428. [13] A.B. Kolomeisky and M.E. Fisher, to be published. 12:10
PM - 1:30 PM LUNCH Chair: George Hentschel, Emory University 1:30
PM - 2:10 PM FUNCTIONAL MOLECULAR
STICKERS: DYNAMIC FORCE SPECTROSCOPY AND GUIDES FOR DESIGN, Armand Ajdari Laboratoire
de Physico-Chimie Thèorique, ESPCI, 10 rue Vauquelin, F-75231 Paris Cédex 05,
France A common micromanipulation strategy to study molecular adhesion complexes is to analyze their response to an increasing pulling force. This provides structural information, as well as indications as to the performance and “strength” of these stickers in their operation in biological or artificial contexts. We build on existing one-trajectory models and analyze simple situations where dissociation (adhesive failure) can occur along either one of two alternative trajectories in the underlying multidimensional energy landscape. A great diversity of behaviors (e.g. non-monotonicity) is found for the unbinding force and time as functions of the rate at which the pulling force is increased. Pull-weakening and strongly pull-strengthening responses can be obtained from simple designs of the energy landscape. We in particular suggest a class of “harpoon” stickers that bind easily but resist strong pulling efficiently. This study furthermore demonstrates the intrinsic difficulty of unambiguously determining features of the energy landscape from single-molecule pulling experiments. In collaboration with Denis Bartolo (a) and Imre Derènyi (b) (a) Laboratoire de Physico-Chimie Thèorique, ESPCI, 10 rue Vauquelin, F-75231 Paris Cédex 05, France (b) Institut Curie, 26 rue d'Ulm, F-75248 Paris Cédex 05, France 2:10 PM - 2:50 PM DYNAMIC FORCE SPECTROSCOPY OF MOLECULES AT SURFACES, Michael Urbakh (urbakh@post.tau.ac.il) School of Chemistry. Tel Aviv University, Ramat Aviv, Tel Aviv, 69978, Israel Experiments that probe mechanical forces on small scales provide a versatile tool for studying molecular adhesion and friction through the response to mechanical stress of single molecules or of nanoscale tips. Here we introduce a generalization of the Tomlinson model to describe the dynamical response of a tip subject to a lateral drive in the context of dynamical force spectroscopy. Our generalization of the Tomlinson model is by including thermal fluctuations. We show that the measured friction forces depend on the microscopic potential and dissipation inherent to the system as well as on the mechanical properties of the set up (i.e. spring constant) and the external noise. Tuning the noise and spring constant offers ways to extract information about the microscopic properties. In collaboration with O.K. Dudko(Tel Aviv), A.E. Filippov(Donetsk, Ukraine) and J. Klafter(Tel Aviv) 2:50
PM - 3:30 PM FORCE-DRIVEN UNFOLDING IN
SINGLE PROTEIN MOLECULES, Miklós SZ Kellermayer (Miklos.Kellermayer.Jr@aok.pte.hu),
University of Pécs, Department of
Biophysics, Szigetiut 12., Pécs, H-7624, Hungary Folding is a not well understood process in which protein molecules acquire their three-dimensional structure. Single- molecule manipulation techniques were used here to explore mechanisms of protein folding and the elastic properties of polypeptide chains. As a model molecule we used the giant muscle protein titin, a modular elastomeric protein. Titin spans half of the striated muscle sarcomere, generates passive muscle force upon stretch, and may serve as a template for sarcomere assembly. Fluorescently labeled strands of titin stretched with meniscus force or by nanomanipulation appeared as strings of bright beads that correspond to compact structures interspersed with faint regions that correspond to loose structural elements. During stretch, compact regions along titin remained stable, while loose segments extended. Measurements, with laser tweezers or atomic force microscopy, of the force required to stretch a single molecule revealed that titin behaves as a highly non-linear entropic spring in which domain unfolding occurs at high (above 30 pN) and refolding at low (~2.5 pN) forces. Comparison of experimental data with predictions of the wormlike chain (WLC) theory revealed a persistence length of up to ~15 ≈ for the single unfolded molecule. The behavior of the partially unfolded titin molecule can be well simulated as serially linked WLCís with distinct elastic properties. During repeated stretch-release cycles titin became mechanically worn-out in a process we call "molecular fatigue." Since titin's molecular fatigue occurs in a physiologically relevant force range, the process may play an important role in dynamically adjusting striated muscle's response to the recent history of mechanical perturbations. Single-molecule techniques may provide unique insights into the elasticity and structural transitions in protein molecules. Chair: Tamàs Vicsek, Eötvös Loránd University 3:30
PM - 4:30 PM POSTER PRESENTATION 1 Chair: Greg Huber, University of Massachusetts 4:30
PM - 5:10 PM RECTIFIED BROWNIAN MOTION
AND THE MECHANISM OF KINESIN, Ronald F. Fox (ron.fox@physics.gatech.edu)
School of Physics, Georgia Institute of
Technology, Atlanta, Georgia 30332 Rectified Brownian motion is a general nanobiological mechanism in which chemical energy is used to bias boundary conditions so that mechanical work can be extracted from heat. This mechanism applied to ubiquinone transport, rotary enzymes, ion transporting ATPases and motor proteins such as kinesin. It is argued that the ATP binding kinesin heads act as switches, like their evolutionary relatives, the G-proteins, and do not directly convert chemical energy into work. 5:10
PM - 5:50 PM EVIDENCE FOR REGULATION
OF DYNEIN MOTOR FUNCTION BY A DISEASE-CAUSING GENE, Richard Bert
Vallee (Richard.Vallee@Umassmed.edu)
University of Massachusetts Medical
School, 377 Plantation St., IV Biotech, Worcester, MA 01605 A single major form of cytoplasmic dynein (MAP1C/dynein 1) is involved in a wide range of cellular functions. These include retrograde axonal transport, chromosome movement, mitotic spindle orientation, cytoskeletal reorganization during wound healing and other events, nuclear migration, and the redistribution of a variety of vesicular organelles. Recent evidence has indicated that the human brain developmental disease, lissencephaly, is due to mutations in a dynein regulatory gene, LIS1. We have found that the LIS1 polypeptide coimmunoprecipitates with dynein and its accessory complex dynactin. Perturbation of LIS1 expression in cultured mammalian cells or anti-LIS1 antibody injection produced a marked mitotic dynein phenotype, involving randomization of mitotic spindle orientation, misalignment of chromosomes at kinetochores, and pronounced delays in mitosis. LIS1 clearly localized to the cortex of mitotic cells and to kinetochores, consistent with these results. Current work is aimed at understanding the specific role of LIS1 in regulating dynein activity. We find that LIS1 interacts with several dynein/dynactin polypeptides. We map the interaction with dynein heavy chain to two distinct sites, one within the N-terminal cargo binding domain and the other ~1000 a.a. downstream corresponding to the first of 6 recently identified AAA ATPase repeats. These results implicate LIS1 in coordinating cargo binding and motor activities and will be discussed in terms of current models of dynein motor function. 6:00
PM - 7:30 PM DINNER Chair: Fabio Marchesoni, Universita' di Perugia 7:30 PM - 8:10 PM BINDING ZIPPER: THE ENERGY TRANSDUCTION MECHANISM OF THE F1 ATP SYNTHASE, Hongyun Wang (hongwang@cse.ucsc.edu) School of
Engineering, University of California, Santa Cruz, California 95064 We discuss the molecular mechanism by which the F1 ATP synthase converts ATP hydrolysis free energy into a mechanical torque and vice versa. In the hydrolysis cycle, the ATP binding consists of two major parts: (i) ATP diffusing into the catalytic site from solution (ATP docking) and (ii) the multi-step transition from weak binding to tight binding as bonds form sequentially between ATP and the catalytic site (binding transition). The force is generated at the catalytic site during the binding transition. We call this process the binding zipper. Nucleotide hydrolysis weakens the binding sufficiently and distributes the binding over two products so that the products can be released and the reaction cycle can repeat. The same mechanism may operate in other motors driven by ATP hydrolysis. The force generated in the binding transition may be stored in the enzyme and released in the subsequent reaction steps. So viewed from outside, it may appear that the force is generated in other reaction steps. 8:10
PM - 8:50 PM NANOBIOLOGY: STOCHASTIC
RESONANCE IN ASSEMBLIES OF ION CHANNELS, Peter Hänggi (hanggi@physik.uni-augsburg.de)
Universität Augsburg, Institute of
Physics, Universitätstr. 1, AUGSBURG, Bavaria/Germany, D-86135 Germany By use of a stochastic generalization of the Hodgkin-Huxley model we investigate the phenomena of Stochastic Resonance [1] (SR) and Coherence Resonance (CR) in assemblies of ion channels. For the case of no applied stimulus we demonstrate the existence of an optimal size of the membrane patch for which sole internal noise causes a most regular spiking activity (intrinsic CR) [2,3]. In presence of an applied stimulus we demonstrate that the signal-to- noise ratio exhibits SR vs. decreasing patch sizes (i.e. vs. increasing internal noise strength). SR with external noise occurs only for large sizes which possess sub-optimal internal noise levels [2]. SR in biology is thus seemingly rooted in the collective properties of large ion channel ensembles [2,3]. In contrast, a single ion channel may exhibit SR only if it is principally dwelled in its closed state [4]. [1] L. Gammaitoni, P. Hänggi, P. Jung and F. Marchesoni, Rev. Mod. Phys. 70: 223 (1998). [2] G. Schmid, I. Goychuk and P. Hänggi, Europhys. Lett. 56:22 (2001). [3] P. Jung and J.W. Shuai, Europhys. Lett. 56: 29 (2001). [4] I. Goychuk and P. Hänggi, Phys. Rev. E 61: 4272 (2000). Saturday, October 27, 2001 Chair: Jorge F. Willemsen,
University of Miami 9:00
AM - 9:40 AM STABLE VORTICES IN SOME BIOLOGICAL
PATTERNS, Mehran Kardar (kardar@mail.itp.ucsb.edu) M. I. T., Department of Physics,
Cambridge, MA 02139 Since vortices are natural topological defects, their
appearance in biological patterns involving a vector field is not surprising.
In two distinct situations we ask the question of why the dynamics that
generates such vortices does not then remove them by pair annihilation and
coarsening. In maps of orientation selectivity in the visual cortex, we
relate stability of “pinwheels” to the persistence of lines in natural
images. In mixtures of microtubules and molecular motors asters and vortices
are actively produced by consumption of energy, while their annihilation is
stopped by a process of “arrested coarsening.” 9:40
AM - 10:20 AM PARADOXICAL SPATIAL AND
TEMPORAL PATTERNS, Katja Lindenberg (klindenberg@ucsd.edu)
University of California, San Diego,
9500 Gilman Drive, La Jolla, CA, 92093-0340 We propose a new mechanism for pattern formation based on the global alternation of two dynamics neither of which exhibits patterns. When driven by either one of the separate dynamics, the system goes to a spatially homogeneous state associated with that dynamics. However, when the two dynamics are globally alternated, the system exhibits stationary spatial patterns (rapid switching) or oscillatory spatial patterns (slower switching). In collaboration with J. Buceta and J. M. R. Parrondo. Work inspired by effects seen in flashing ratchets and paradoxical games. 10:20
AM- 10:50 AM BREAK Chair: Diego
del-Castillo-Negrete, Oak Ridge
National Laboratory 10:50
AM - 11:30 AM CHAOTIC TRANSPORT IN
DETERMINISTIC RATCHETS, José L. Mateos (mateos@fisica.unam.mx) Institute
of Physics, UNAM, Ciudad Universitaria, Apartado Postal 20-364, México City,
Distrito Federal, 01000, México The problem of the classical deterministic dynamics of a particle in a periodic asymmetric ratchet potential is addressed. When the inertial term is taken into account, that dynamics becomes chaotic and modify the transport properties. By a comparison between the bifurcation diagram and the current, we identify the origin of the multiple current reversals as bifurcations, usually from a chaotic to a periodic regime. Close to this crisis bifurcations, we observe trajectories revealing intermittent chaos, anomalous deterministic diffusion and Levy-like flights. We extend our previous work (Mateos, PRL 84 (2000) 258), to include the case of coexisting attractors in phase space that transport particles in opposite directions. 11:30
AM - 12:10 PM CONTROL OF CURRENT IN
DETERMINISTIC INERTIA RATCHETS, Miguel C. Arizmendi (arizmend@fi.mdp.edu.ar)
Univ. Nac. de Mar del Plata, Departamento de Física, Av. J. B. Justo 4302,
Fac. de Ingeniería, Mar del Plata, 7600, Argentina Inertial ratchets, even in the absence of noise have a very complex dynamics, including chaotic motion and multiple reversals in the current direction by changing the strength of the external force. The control of current direction is especially interesting for technological applications such as microscopic particle separation although it seems very difficult because of the irregularity of the current reversals appearances. The possibility of control of current appears as a consequence of a locking process associated with different mean velocity attractors. The strength of the external force and the amount of quenched disorder are used as control parameters on both single and multiparticle inertial ratchet systems. In collaboration with F. Family (a) and H. Larrondo (b) (a) Department of Physics, Emory University, Atlanta, GA 30322, USA (b) Depto. De Fisica, UNMDP, Av. J. B. Justo 4302, 7600 Mar del Plata, Argentina 12:10
PM - 1:30 PM LUNCH Chair: Álvaro L.
Salas-Brito, UAM-Azcapotzalco 1:30
PM - 2:10 PM TRANSPORT THROUGH THE
NUCLEAR PORE, Michael Elbaum (michael.elbaum@weizmann.ac.il)
Weizmann Institute of Science, Dept of
Materials and Interfaces, Rehovot, 76100, Israel The eukaryotic cell is divided into two major compartments, the nucleus and the cytoplasm. A double lipid bilayer membrane, the nuclear envelope, divides between them. Spanning both bilayers are large multiprotein channels known as nuclear pores. These are responsible for the transport of macromolecules into and out of the nucleus. While the passage of small molecules takes place by passive diffusion, larger ones including most proteins and protein-RNA complexes are actively and selectively pumped in one or the other direction. As such, the nuclear pore is a bone fide molecular machine. Yet no force-generating element has been found to explain its operation as a pump. Instead, biochemists have proposed a mechanism based on a transport-usher molecule and a switch of molecular affinities that releases the cargo on one side only. The talk will discuss a simulation of this model, as well as experiments on the passage of DNA through the nuclear pores. While not part of normal cell physiology, the latter is the basis for many types of viral infection, as well as proposed strategies for genetic therapy. 2:10
PM - 2:50 PM SIMULATING DNA
TRANSLOCATION THROUGH A PORE, Tamàs Vicsek (vicsek@angel.elte.hu)
Department of Biological Physics, ELTE,
Pazmany P. Stny 1A, Budapest, 1117, Hungary The dynamics of polymer translocation through a pore has been the subject of interesting recent theoretical and experimental works. We have considered theoretical estimates and performed computer simulations in 3D to understand the mechanism of DNA uptake into the cell nucleus, a phenomenon experimentally investigated with the help of attaching a small bead to the free end of the double spiral. We focused on several questions: i) What are the actual forces (of dynamic and entropic origin) acting between the parts of the pore-wall-bead complex, ii) what are the pulling mechanisms iii) and how the dynamics of the uptake is modified by the bead attached to the end of the DNA. Our theoretical estimates and computer simulations suggest a new interpretation of the experimental observations. In addition, Our approach allows testing various existing hypotheses on the dynamics of translocation of DNA through a hole as well as on the forces arising when biopolymers are pulled. In collaboration with Z. Farkas, I Derènyi, T. Fulop 2:50
PM - 3:30 PM THE BROWNIAN RATCHET AND
POWER STROKE MODELS FOR POST-TRANSLATIONAL PROTEIN TRANSLOCATION INTO THE
ENDOPLASMIC RETICULUM, Timothy C. Elston (elston@unity.ncsu.edu) North Carolina State University,
Biomathematics Graduate Program/Department of Statistics, Campus Box 8203,
Raleigh, NC 27695-8203 The Brownian ratchet and power stroke models for
post-translational protein translocation are compared against experimental
data for import into the endoplasmic reticulum. The data sets are
simultaneously fit using a least-squares criterion, and both models are found
to accurately reproduce the experimental results. A likelihood-ratio test
reveals that the optimal fit of the Brownian ratchet model, which contains
one fewer free parameter, does not differ significantly from that of the
power stroke model. Therefore, the data considered here can not be used to
reject this import mechanism. The models are further analyzed using the
estimated parameters to make experimentally testable predictions. Chair: C. Miguel
Arizmendi, Universidad Nacional de Mar
del Plata 3:30
PM - 4:30 PM POSTER PRESENTATION II Chair: Franco Nori, University of Michigan 4:30 PM - 5:10 PM MOTORS ON THE MESOSCOPIC TO MOLECULAR
SCALE, Markus Porto (porto@mpipks-dresden.mpg.de) Max-Planck-Institut für Physik komplexer
Systeme, Nothnitzer Str. 38, Dresden, 01187, Germany A recently introduced approach to build microscopic engines on the mesoscopic to molecular scale is discussed. The proposed concept allows the motor to move translationally or rotationally and to perform useful functions such as pulling of a cargo. Characteristic of the approach is the intrinsic possibility to determine dynamically the velocity and directionality of the motion. Possible realizations are proposed, and some ingredients are introduced, such as turns and switches, which are important for creating a microscopic “railway system.” In collaboration with Michael Urbakh and Joseph Klafter,
Tel Aviv University, Israel 5:10
PM - 5:50 PM FORMATION, INTERACTION,
AND FUNCTION OF MEMBRANE TUBES, Imre Derènyi (Imre.Derenyi@curie.fr) Institut
Curie, 11 rue Pierre et Marie Curie, Paris 75231, France In certain stages of the cell cycle highly dynamic tubular membrane networks are formed. The exact role of these networks is not known but they are most probably involved in the transport and sorting of proteins and lipids. The formation and motion of membrane tubes are thought to involve motor proteins that are able to pull on the membrane as they move along the cytoskeleton. In my presentation I will talk about the theoretical aspects of the formation and interaction of membrane tubes, illustrated by recent experiments, and I will also investigate the possible role of these tubes in protein and lipid segregation. 5:50
PM - 6:10 PM FINAL THOUGHTS, Fereydoon
Family (phyff@emory.edu)
Department of Physics, Emory
University, Atlanta 6:30
PM - 8:00 PM DINNER (Dinning Room) Information and RegistrationFor conference information and registration, click here. |
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