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Yu WC. Translocation of Heterogeneous Flexible Polymers Assisted by Binding Particles. CHINESE JOURNAL OF POLYMER SCIENCE 2020. [DOI: 10.1007/s10118-020-2387-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Suhonen PM, Linna RP. Chaperone-assisted translocation of flexible polymers in three dimensions. Phys Rev E 2016; 93:012406. [PMID: 26871100 DOI: 10.1103/physreve.93.012406] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Indexed: 06/05/2023]
Abstract
Polymer translocation through a nanometer-scale pore assisted by chaperones binding to the polymer is a process encountered in vivo for proteins. Studying the relevant models by computer simulations is computationally demanding. Accordingly, previous studies are either for stiff polymers in three dimensions or flexible polymers in two dimensions. Here, we study chaperone-assisted translocation of flexible polymers in three dimensions using Langevin dynamics. We show that differences in binding mechanisms, more specifically, whether a chaperone can bind to a single site or multiple sites on the polymer, lead to substantial differences in translocation dynamics in three dimensions. We show that the single-binding mode leads to dynamics that is very much like that in the constant-force driven translocation and accordingly mainly determined by tension propagation on the cis side. We obtain β≈1.26 for the exponent for the scaling of the translocation time with polymer length. This fairly low value can be explained by the additional friction due to binding particles. The multiple-site binding leads to translocation the dynamics of which is mainly determined by the trans side. For this process we obtain β≈1.36. This value can be explained by our derivation of β=4/3 for constant-bias translocation, where translocated polymer segments form a globule on the trans side. Our results pave the way for understanding and utilizing chaperone-assisted translocation where variations in microscopic details lead to rich variations in the emerging dynamics.
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Affiliation(s)
- P M Suhonen
- Department of Computer Science, Aalto University, Post Office Box 15400, FI-00076 Aalto, Finland
| | - R P Linna
- Department of Computer Science, Aalto University, Post Office Box 15400, FI-00076 Aalto, Finland
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Assenza S, De Los Rios P, Barducci A. Quantifying the role of chaperones in protein translocation by computational modeling. Front Mol Biosci 2015; 2:8. [PMID: 25988176 PMCID: PMC4428437 DOI: 10.3389/fmolb.2015.00008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Accepted: 02/28/2015] [Indexed: 01/26/2023] Open
Abstract
The molecular chaperone Hsp70 plays a central role in the import of cytoplasmic proteins into organelles, driving their translocation by binding them from the organellar interior. Starting from the experimentally-determined structure of the E. coli Hsp70, we computed, by means of molecular simulations, the effective free-energy profile for substrate translocation upon chaperone binding. We then used the resulting free energy to quantitatively characterize the kinetics of the import process, whose comparison with unassisted translocation highlights the essential role played by Hsp70 in importing cytoplasmic proteins.
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Affiliation(s)
- Salvatore Assenza
- Laboratoire de Biophysique Statistique, Ecole Polytechnique Fédérale de Lausanne Lausanne, Switzerland
| | - Paolo De Los Rios
- Laboratoire de Biophysique Statistique, Ecole Polytechnique Fédérale de Lausanne Lausanne, Switzerland
| | - Alessandro Barducci
- Laboratoire de Biophysique Statistique, Ecole Polytechnique Fédérale de Lausanne Lausanne, Switzerland
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Palyulin VV, Ala-Nissila T, Metzler R. Polymer translocation: the first two decades and the recent diversification. SOFT MATTER 2014; 10:9016-37. [PMID: 25301107 DOI: 10.1039/c4sm01819b] [Citation(s) in RCA: 139] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Probably no other field of statistical physics at the borderline of soft matter and biological physics has caused such a flurry of papers as polymer translocation since the 1994 landmark paper by Bezrukov, Vodyanoy, and Parsegian and the study of Kasianowicz in 1996. Experiments, simulations, and theoretical approaches are still contributing novel insights to date, while no universal consensus on the statistical understanding of polymer translocation has been reached. We here collect the published results, in particular, the famous-infamous debate on the scaling exponents governing the translocation process. We put these results into perspective and discuss where the field is going. In particular, we argue that the phenomenon of polymer translocation is non-universal and highly sensitive to the exact specifications of the models and experiments used towards its analysis.
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Affiliation(s)
- Vladimir V Palyulin
- Institute for Physics & Astronomy, University of Potsdam, D-14476 Potsdam-Golm, Germany.
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Yu W, Luo K. Polymer translocation through a nanopore driven by binding particles: influence of chain rigidity. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 90:042708. [PMID: 25375524 DOI: 10.1103/physreve.90.042708] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2014] [Indexed: 06/04/2023]
Abstract
We investigate the influence of chain rigidity on the dynamics of polymer translocation in the presence of binding particles (BPs) through a nanopore using two-dimensional Langevin dynamics simulations. With increasing chain rigidity κ, the mean translocation time 〈τ〉 increases monotonically due to an increase in the radius of gyration and a decrease in the center of mass velocity. Particularly for weak binding, we further find that 〈τ〉 shows a power-law behavior with the persistence length lp. Analysis indicates a scaling relation between the average velocity of the center of mass of a chain 〈vc.m.〉 and lp. As the chain becomes stiffer, the distribution of the translocation time τ approximates the Gaussian distribution and gets broader with the peak position being shifted towards longer translocation time. The corresponding translocation coordinate smax of the maximum waiting time gets smaller with increasing chain rigidity. Finally, under an extremely low BP concentration, 〈τ〉 shows a minimum for small κ, while it decreases monotonically for large κ with increasing binding energy. Our results suggest a nontrivial effect of the intrinsic property of chains on the dynamics of polymer translocation driven by BPs.
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Affiliation(s)
- Wancheng Yu
- CAS Key Laboratory of Soft Matter Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, Anhui Province 230026, People's Republic of China
| | - Kaifu Luo
- CAS Key Laboratory of Soft Matter Chemistry, Collaborative Innovation Center of Chemistry for Energy Materials, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, Anhui Province 230026, People's Republic of China
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Griesemer M, Young C, Robinson AS, Petzold L. BiP clustering facilitates protein folding in the endoplasmic reticulum. PLoS Comput Biol 2014; 10:e1003675. [PMID: 24991821 PMCID: PMC4081015 DOI: 10.1371/journal.pcbi.1003675] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Accepted: 05/03/2014] [Indexed: 12/26/2022] Open
Abstract
The chaperone BiP participates in several regulatory processes within the endoplasmic reticulum (ER): translocation, protein folding, and ER-associated degradation. To facilitate protein folding, a cooperative mechanism known as entropic pulling has been proposed to demonstrate the molecular-level understanding of how multiple BiP molecules bind to nascent and unfolded proteins. Recently, experimental evidence revealed the spatial heterogeneity of BiP within the nuclear and peripheral ER of S. cerevisiae (commonly referred to as 'clusters'). Here, we developed a model to evaluate the potential advantages of accounting for multiple BiP molecules binding to peptides, while proposing that BiP's spatial heterogeneity may enhance protein folding and maturation. Scenarios were simulated to gauge the effectiveness of binding multiple chaperone molecules to peptides. Using two metrics: folding efficiency and chaperone cost, we determined that the single binding site model achieves a higher efficiency than models characterized by multiple binding sites, in the absence of cooperativity. Due to entropic pulling, however, multiple chaperones perform in concert to facilitate the resolubilization and ultimate yield of folded proteins. As a result of cooperativity, multiple binding site models used fewer BiP molecules and maintained a higher folding efficiency than the single binding site model. These insilico investigations reveal that clusters of BiP molecules bound to unfolded proteins may enhance folding efficiency through cooperative action via entropic pulling.
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Affiliation(s)
- Marc Griesemer
- Department of Applied Mathematics, University of California, Merced, Merced, California, United States of America
- * E-mail:
| | - Carissa Young
- Department of Chemical Engineering, University of Delaware, Newark, Delaware, United States of America
| | - Anne S. Robinson
- Department of Chemical Engineering, University of Delaware, Newark, Delaware, United States of America
- Department of Chemical and Biomolecular Engineering, Tulane University, New Orleans, Louisiana, United States of America
| | - Linda Petzold
- Department of Computer Science, University of California, Santa Barbara, Santa Barbara, California, United States of America
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Simulating the pulling of stalled elongated peptide from the ribosome by the translocon. Proc Natl Acad Sci U S A 2013; 110:10195-200. [PMID: 23729811 DOI: 10.1073/pnas.1307869110] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The nature of the coupling between the stalling of the elongated nascent peptide chain in the ribosome and its insertion through the translocon is analyzed, focusing on the recently discovered biphasic force that overcomes the stalling barrier. The origin of this long-range coupling is explored by coarse-grained simulations that combine the translocon (TR) insertion profile and the effective chemical barrier for the extension of the nascent chain in the ribosome. Our simulation determined that the inserted H segment is unlikely to climb the TR barrier in parallel with the peptide synthesis chemical step and that the nascent chain should first overcome the chemical barriers and move into the ribosome-TR gap region before the insertion into the TR tunnel. Furthermore, the simulations indicate that the coupled TR-chemistry free energy profile accounts for the biphasic force. Apparently, although the overall elongation/insertion process can be depicted as a tug-of-war between the forces of the TR and the ribosome, it is actually a reflection of the combined free-energy landscape. Most importantly, the present study helps to relate the experimental observation of the biphasic force to crucial information about the elusive path and barriers of the TR insertion process.
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Yu W, Ma Y, Luo K. Translocation of stiff polymers through a nanopore driven by binding particles. J Chem Phys 2012; 137:244905. [DOI: 10.1063/1.4772658] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Zhang B, Miller TF. Long-timescale dynamics and regulation of Sec-facilitated protein translocation. Cell Rep 2012; 2:927-37. [PMID: 23084746 PMCID: PMC3483636 DOI: 10.1016/j.celrep.2012.08.039] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2012] [Revised: 07/21/2012] [Accepted: 08/31/2012] [Indexed: 01/11/2023] Open
Abstract
We present a coarse-grained modeling approach that spans the nanosecond- to minute-timescale dynamics of cotranslational protein translocation. The method enables direct simulation of both integral membrane protein topogenesis and transmembrane domain (TM) stop-transfer efficiency. Simulations reveal multiple kinetic pathways for protein integration, including a mechanism in which the nascent protein undergoes slow-timescale reorientation, or flipping, in the confined environment of the translocon channel. Competition among these pathways gives rise to the experimentally observed dependence of protein topology on ribosomal translation rate and protein length. We further demonstrate that sigmoidal dependence of stop-transfer efficiency on TM hydrophobicity arises from local equilibration of the TM across the translocon lateral gate, and it is predicted that slowing ribosomal translation yields decreased stop-transfer efficiency in long proteins. This work reveals the balance between equilibrium and nonequilibrium processes in protein targeting, and it provides insight into the molecular regulation of the Sec translocon.
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Affiliation(s)
- Bin Zhang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA
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Yu W, Luo K. Chaperone-Assisted Translocation of a Polymer through a Nanopore. J Am Chem Soc 2011; 133:13565-70. [DOI: 10.1021/ja204892z] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Wancheng Yu
- CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, Anhui Province 230026, P. R. China
| | - Kaifu Luo
- CAS Key Laboratory of Soft Matter Chemistry, Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, Anhui Province 230026, P. R. China
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Tomkiewicz D, Nouwen N, Driessen AJM. Pushing, pulling and trapping--modes of motor protein supported protein translocation. FEBS Lett 2007; 581:2820-8. [PMID: 17466297 DOI: 10.1016/j.febslet.2007.04.015] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2007] [Revised: 04/01/2007] [Accepted: 04/11/2007] [Indexed: 11/19/2022]
Abstract
Protein translocation across the cellular membranes is an ubiquitous and crucial activity of cells. This process is mediated by translocases that consist of a protein conducting channel and an associated motor protein. Motor proteins interact with protein substrates and utilize the free energy of ATP binding and hydrolysis for protein unfolding, translocation and unbinding. Since motor proteins are found either at the cis- or trans-side of the membrane, different mechanisms for translocation have been proposed. In the Power stroke model, cis-acting motors are thought to push, while trans-motors pull on the substrate protein during translocation. In the Brownian ratchet model, translocation occurs by diffusion of the unfolded polypeptide through the translocation pore while directionality is achieved by trapping and refolding. Recent insights in the structure and function of the molecular motors suggest that different mechanisms can be employed simultaneously.
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Affiliation(s)
- Danuta Tomkiewicz
- Department of Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
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Ambjörnsson T, Lomholt MA, Metzler R. Directed motion emerging from two coupled random processes: translocation of a chain through a membrane nanopore driven by binding proteins. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2005; 17:S3945-S3964. [PMID: 21690734 DOI: 10.1088/0953-8984/17/47/021] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We investigate the translocation of a stiff polymer consisting of M monomers through a nanopore in a membrane, in the presence of binding particles (chaperones) that bind onto the polymer, and partially prevent backsliding of the polymer through the pore. The process is characterized by the rates: k for the polymer to make a diffusive jump through the pore, q for unbinding of a chaperone, and the rate qκ for binding (with a binding strength κ); except for the case of no binding κ = 0 the presence of the chaperones gives rise to an effective force that drives the translocation process. In more detail, we develop a dynamical description of the process in terms of a (2+1)-variable master equation for the probability of having m monomers on the target side of the membrane with n bound chaperones at time t. Emphasis is put on the calculation of the mean first passage time [Formula: see text] as a function of total chain length M. The transfer coefficients in the master equation are determined through detailed balance, and depend on the relative chaperone size λ and binding strength κ, as well as the two rate constants k and q. The ratio γ = q/k between the two rates determines, together with κ and λ, three limiting cases, for which analytic results are derived: (i) for the case of slow binding ([Formula: see text]), the motion is purely diffusive, and [Formula: see text] for large M; (ii) for fast binding ([Formula: see text]) but slow unbinding ([Formula: see text]), the motion is, for small chaperones λ = 1, ratchet-like, and [Formula: see text]; (iii) for the case of fast binding and unbinding dynamics ([Formula: see text] and [Formula: see text]), we perform the adiabatic elimination of the fast variable n, and find that for a very long polymer [Formula: see text], but with a smaller prefactor than for ratchet-like dynamics. We solve the general case numerically as a function of the dimensionless parameters λ, κ and γ, and compare to the three limiting cases.
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Affiliation(s)
- Tobias Ambjörnsson
- NORDITA-Nordic Institute for Theoretical Physics, Blegdamsvej 17, DK-2100 Copenhagen Ø, Denmark
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Sikorski A, Romiszowski P. Computer simulation of polypeptide translocation through a nanopore. J Mol Model 2005; 11:379-84. [PMID: 15806388 DOI: 10.1007/s00894-005-0254-9] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2004] [Accepted: 02/07/2005] [Indexed: 11/26/2022]
Abstract
A simplified model of polypeptide chains was designed and studied by means of computer simulations. Chains were represented by a sequence of united atoms located at the positions of the alpha-carbons. A further assumption was the lattice approximation for the chains. We used a (310) lattice, which was found useful for studying properties of proteins. The force field used consisted of a long-range contact potential between amino-acid residues and a local preference for forming alpha-helical states. The chain consisted of two kinds of residues: hydrophilic (P) and hydrophobic (H) ones forming model helical septets--HHPPHPP--in a sequence. The chains were placed near an impenetrable surface with a square hole in it. The size of the hole was comparable or smaller than the size of a chain. The properties of these model chains were determined using the Monte-Carlo simulation method. During the simulations, translocation of the chain through the hole in the wall was observed. The influence of the chain length, the temperature differences on both sides of the wall and the force field on the chain properties were investigated. It was shown that the translocation time scales as N(2.2) and it was found that the presence of the local helical potential significantly slows down the process of translocation. [Figure: see text]. The snapshots of typical chain's conformation obtained during the simulation for chain consisted of N = 60. The values of the local potential epsilon(loc) = -8.
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Affiliation(s)
- Andrzej Sikorski
- Department of Chemistry, University of Warsaw, Pasteura 1, 02-093, Warszawa, Poland
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Abstract
We investigate the translocation of a stiff polymer through a nanopore in a membrane, in the presence of binding particles (chaperones) that bind reversibly to the polymer on both sides of the membrane. A bound chaperone covers one (univalent binding) or many (multivalent binding) binding sites. Assuming that the diffusion of the chaperones is fast compared to the rate of translocation we describe the process by a one-dimensional master equation. We expand previous models by a detailed study of the effective force in the master equation, which is obtained by the appropriate statistical mechanical average over the chaperone states. The dependence of the force on the degree of valency (the number of binding sites occupied by a chaperone) is studied in detail. We obtain finite size corrections (to the thermodynamical expression for the force), which, for univalent binding, can be expressed analytically. We finally investigate the mean velocity for translocation as a function of chaperone binding strength and size. For both univalent and multivalent binding simple results are obtained for the case of a sufficiently long translocating polymer.
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Affiliation(s)
- Tobias Ambjörnsson
- NORDITA (Nordic Institute for Theoretical Physics), Blegdamsvej 17, DK-2100 Copenhagen Ø, Denmark.
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Rial DV, Ottado J, Ceccarelli EA. Precursors with altered affinity for Hsp70 in their transit peptides are efficiently imported into chloroplasts. J Biol Chem 2003; 278:46473-81. [PMID: 12970339 DOI: 10.1074/jbc.m306684200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein import into chloroplasts is postulated to occur with the involvement of molecular chaperones. We have determined that the transit peptide of ferredoxin-NADP(H) reductase precursor binds preferentially to an Hsp70 from chloroplast stroma. To investigate the role of Hsp70 molecular chaperones in chloroplast protein import, we analyzed the import into pea chloroplasts of preproteins with decreased Hsp70 binding affinity in their transit peptides. Our results indicate that the precursor with the lowest affinity for Hsp70 molecular chaperones in its transit peptide was imported to chloroplasts with similar apparent Km as the wild type precursor and a 2-fold increase in Vmax. Thus, a strong interaction between chloroplast stromal Hsp70 and the transit peptide seems not to be essential for protein import. These results indicate that in chloroplasts the main unfolding force during protein import may be applied by molecular chaperones other than Hsp70s. Although stromal Hsp70s undoubtedly participate in chloroplast biogenesis, the role of these molecular chaperones in chloroplast protein translocation differs from the one proposed in the mechanisms postulated up to date.
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Affiliation(s)
- Daniela V Rial
- Molecular Biology Division, Rosario Institute of Molecular & Cellular Biology, Faculty of Biochemical and Pharmaceutical Sciences, National University of Rosario, Suipacha 531, S2002LRK Rosario, Argentina
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Di Marzio EA, Kasianowicz JJ. Phase transitions within the isolated polymer molecule: Coupling of the polymer threading a membrane transition to the helix-random coil, the collapse, the adsorption, and the equilibrium polymerization transitions. J Chem Phys 2003. [DOI: 10.1063/1.1603725] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Spees JL, Chang SA, Mykles DL, Snyder MJ, Chang ES. Molt cycle–dependent molecular chaperone and polyubiquitin gene expression in lobster. Cell Stress Chaperones 2003; 8:258-64. [PMID: 14984059 PMCID: PMC514879 DOI: 10.1379/1466-1268(2003)008<0258:mcmcap>2.0.co;2] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Lobster claw muscle undergoes atrophy in correlation with increasing ecdysteroid (steroid molting hormone) titers during premolt. In vivo molecular chaperone (constitutive heat shock protein 70 [Hsc70], heat shock protein 70 [Hsp70], and Hsp90) and polyubiquitin messenger ribonucleic acid (mRNA) levels were examined in claw and abdominal muscles from individual premolt or intermolt lobsters. Polyubiquitin gene expression was assayed as a marker for muscle atrophy. Both Hsc70 and Hsp90 mRNA levels were significantly induced in premolt relative to intermolt lobster claw muscle, whereas Hsp70 mRNA levels were not. Hsp90 gene expression was significantly higher in premolt claw muscle when compared with abdominal muscle. Polyubiquitin mRNA levels were elevated in premolt when compared with intermolt claw muscle and significantly elevated relative to premolt abdominal muscle.
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Affiliation(s)
- Jeffrey L Spees
- Bodega Marine Laboratory, University of California, PO Box 247, Bodega Bay, CA 94923, USA
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Elston TC. The brownian ratchet and power stroke models for posttranslational protein translocation into the endoplasmic reticulum. Biophys J 2002; 82:1239-53. [PMID: 11867441 PMCID: PMC1301927 DOI: 10.1016/s0006-3495(02)75480-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A quantitative analysis of experimental data for posttranslational translocation into the endoplasmic reticulum is performed. This analysis reveals that translocation involves a single rate-limiting step, which is postulated to be the release of the signal sequence from the translocation channel. Next, the Brownian ratchet and power stroke models of translocation are compared against the data. 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 cannot be used to reject this import mechanism. The models are further analyzed using the estimated parameters to make experimentally testable predictions.
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Affiliation(s)
- Timothy C Elston
- Biomathematics Graduate Program/Department of Statistics, North Carolina State University, Raleigh, North Carolina 27695-8203, USA.
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