scholarly journals VASP is a processive actin polymerase that requires monomeric actin for barbed end association

2010 ◽  
Vol 191 (3) ◽  
pp. 571-584 ◽  
Author(s):  
Scott D. Hansen ◽  
R. Dyche Mullins
Keyword(s):  
Ionic Strength ◽  
Total Internal Reflection ◽  
Molecular Mechanisms ◽  
Binding Modes ◽  
Cellular Functions ◽  
Actin Networks ◽  
Filament Assembly ◽  
Binding Event ◽  
Low Ionic Strength

Ena/VASP proteins regulate the actin cytoskeleton during cell migration and morphogenesis and promote assembly of both filopodial and lamellipodial actin networks. To understand the molecular mechanisms underlying their cellular functions we used total internal reflection fluorescence microscopy to visualize VASP tetramers interacting with static and growing actin filaments in vitro. We observed multiple filament binding modes: (1) static side binding, (2) side binding with one-dimensional diffusion, and (3) processive barbed end tracking. Actin monomers antagonize side binding but promote high affinity (Kd = 9 nM) barbed end attachment. In low ionic strength buffers, VASP tetramers are weakly processive (Koff = 0.69 s−1) polymerases that deliver multiple actin monomers per barbed end–binding event and effectively antagonize filament capping. In higher ionic strength buffers, VASP requires profilin for effective polymerase and anti-capping activity. Based on our observations, we propose a mechanism that accounts for all three binding modes and provides a model for how VASP promotes actin filament assembly.

Preparation Of Antithrombin, High Activity Heparin And A Heparin-Antithrombin Complex By A Rapid Two-Step Affinity Method

1981 ◽  
Author(s):  
R Jordan ◽  
T Zuffi ◽  
M Fournel ◽  
D Schroeder
Keyword(s):  
Ionic Strength ◽  
High Activity ◽  
Tight Binding ◽  
Therapeutic Benefit ◽  
Purification Scheme ◽  
The Matrix ◽  
Low Ionic Strength ◽  
Potential Therapeutic Benefit

The tight binding affinity of antithrombin for heparin makes possible a relatively selective purification scheme based on salt elution from heparin-Sepharose. We have found, however, that purity can often be greatly increased if the elution is carried out with soluble heparin instead. This heparin can be removed from the antithrombin, either in whole or part, by a second affinity step on Concanavalin A Sepharose. The antithrombin, which binds to the matrix through its glycosidic moieties, retains its ability to bind heparin at physiological ionic strengths. Thus, the complex of antithrombin and heparin is readily isolated free of unbound heparin species. The complex can be eluted intact with low ionic strength buffers containing sugars which compete for binding to the lectin. Alternatively, the high activity heparin (400–500 units/mg) can be obtained separately by a 1 M NaCl wash which is then followed by a carbohydrate wash to obtain the purified antithrombin.We have made certain preliminary biochemical and anticoagulant characterizations of these materials. Not unexpectedly, both the high activity heparin and its complex with antithrombin show significantly greater in vitro potency in comparison to unfractionated heparin. In vivo anticoagulant efficacy, as evaluated in a rabbit infusion model, confirmed the in vitro findings and further suggests some potential therapeutic benefit may be derived from infusion of a preformed heparin-antithrombin complex.

scholarly journals Release of poly a(+) messenger RNA from rat liver rough microsomes upon disassembly of bound polysomes

1977 ◽  
Vol 74 (2) ◽  
pp. 414-427 ◽  
Author(s):  
J Kruppa ◽  
DD Sabatini
Keyword(s):  
Ionic Strength ◽  
Rat Liver ◽  
Messenger Rna ◽  
High Salt ◽  
Salt Medium ◽  
Ribosomal Subunits ◽  
Microsomal Membranes ◽  
Low Ionic Strength

Several procedures were used to disassemble rat liver rough microsomes (RM) into ribosomal subunits, mRNA, and ribosome-stripped membrane vesicles in order to examine the nature of the association between the mRNA of bound polysomes and the microsomal membranes. The fate of the mRNA molecules after ribosome release was determined by measuring the amount of pulse-labeled microsomal RNA in each fraction which was retained by oligo-dT cellulose or by measuring the poly A content by hybridization to radioactive poly U. It was found that ribosomal subunits and mRNA were simultaneously released from the microsomal membranes when the ribosomes were detached by: (a) treatment with puromycin in a high salt medium containing Mg++, (b) resuspension in a high salt medium lacking Mg++, and (c) chelation of Mg++ by EDTA or pyrophosphate. Poly A-containing mRNA fragments were extensively released from RM subjected to a mild treatment with pancreatic RNase in a medium of low ionic strength. This indicates that the 3' end of the mRNA is exposed on the outer microsomal surface and is not directly bound to the membranes. Poly A segments of bound mRNA were also accessible to [(3)H] poly U for in situ hybridization in glutaraldehyde-fixed RM. Rats were treated with drugs which inhibit translation after formation of the first peptide bonds or interfere with the initiation of protein synthesis. After these treatments inactive monomeric ribosomes, as well as ribosomes bearing mRNA, remained associated with their binding sites in microsomes prepared in media of low ionic strength. However, because there were no linkages provided by nascent chains, ribosomes, and mRNA, molecules were released from the microsomal membranes without the need of puromycin, by treatment with a high salt buffer containing Mg++. Thus, both in vivo and in vitro observations are consistent with a model in which mRNA does not contribute significantly to the maintenance of the interaction between bound polysomes and endoplasmic reticulum membranes in rat liver hepatocytes.

scholarly journals Isolated beta-heavy chain subunit of dynein translocates microtubules in vitro.

1988 ◽  
Vol 107 (5) ◽  
pp. 1793-1797 ◽  
Author(s):  
W S Sale ◽  
L A Fox
Keyword(s):  
Ionic Strength ◽  
Sea Urchin ◽  
Heavy Chain ◽  
Glass Surface ◽  
Functional Assay ◽  
Atpase Subunits ◽  
Low Ionic Strength ◽  
Intermediate Chains ◽  
Sea Urchin Sperm

Our goal was to assess the microtubule translocating ability of individual ATPase subunits of outer arm dynein. Solubilized outer arm dynein from sea urchin sperm (Stronglocentrotus purpuratus) was dissociated into subunits by low ionic strength buffer and fractionated by zonal centrifugation. Fractions were assessed by an in vitro functional assay wherein microtubules move across a glass surface to which isolated dynein fractions had been absorbed. Microtubule gliding activity was coincident with the 12-S beta-heavy chain-intermediate chain 1 ATPase fractions (beta/IC1). Neither the alpha-heavy chain nor the intermediate chains 2 and 3 fractions coincided with microtubule gliding activity. The beta/IC1 ATPase induced very rapid gliding velocities (9.7 +/- 0.88 micron/s, range 7-11.5 micron/s) in 1 mM ATP-containing motility buffers. In direct comparison, isolated intact 21-S outer arm dynein, from which the beta/IC1 fraction was derived, induced slower microtubule gliding rates (21-S dynein, 5.6 +/- 0.7 micron/s; beta/IC1, 8.7 +/- 1.2 micron/s). These results demonstrate that a single subdomain in dynein, the beta/IC1 ATPase, is sufficient for microtubule sliding activity.

scholarly journals Accessibility of epitopes on fibrin clots and fibrinogen gels

Blood ◽  
1991 ◽  
Vol 77 (7) ◽  
pp. 1469-1475 ◽  
Author(s):  
R Procyk ◽  
B Kudryk ◽  
S Callender ◽  
B Blomback
Keyword(s):  
Monoclonal Antibody ◽  
Clinical Trials ◽  
Ionic Strength ◽  
Factor Xiii ◽  
Imaging Agent ◽  
Low Ionic Strength ◽  
Clot Structure ◽  
Radiolabeled Antibodies ◽  
Fibrin Clots

Abstract Radiolabeled antibodies were perfused into fibrin clots and fibrinogen gels formed in vitro to assess the reactivity of selected epitopes. An antifibrinogen monoclonal antibody (MoAb) (antibody 1D4/xl-f), directed against an epitope in the A alpha-chain C-terminal region (A alpha 241– 476), bound to 35% of the epitope in crosslinked fibrin clots and 37% of the same epitope in factor XIII-induced fibrinogen gel networks. A different MoAb (4–2/xl-f, anti gamma 392–406) bound to only 7% of the epitope in both fibrin and fibrinogen gels. As expected, an antifibrin MoAb (antibody T2G1, antiB beta 15–21) did not bind to fibrinogen gels, but bound to fibrin, although to only 14% of the available T2G1- reactive epitopes. An antibody that does not recognize fibrin (antibody 1–8C6, antiB beta 1–21) predictably did not bind to fibrin clots and bound to 35% of the 1–8C6 epitopes present in fibrinogen gels, a level of binding also observed with antibody T2G1 and fibrinogen gels only after the latter were treated with thrombin. T2G1 epitope expression was affected much more than 1D4/xl-f epitope expression in clots formed in buffers of high or low ionic strength, conditions known to influence clot structure. Studies on the availability, in quantitative terms, of the T2G1-reactive epitope in fibrin clots is of particular importance because this antibody is currently being used in clinical trials as a clot imaging agent.

scholarly journals Tiny Actors in the Big Cellular World: Extracellular Vesicles Playing Critical Roles in Cancer

2020 ◽  
Vol 21 (20) ◽  
pp. 7688 ◽  
Author(s):  
Ancuta Jurj ◽  
Cecilia Pop-Bica ◽  
Ondrej Slaby ◽  
Cristina D. Ştefan ◽  
William C. Cho ◽  
...  
Keyword(s):  
Extracellular Vesicles ◽  
Molecular Mechanisms ◽  
Recipient Cell ◽  
Cell Communication ◽  
Therapeutic Agents ◽  
Bioactive Molecules ◽  
Cellular Functions ◽  
Membrane Bound

Communications among cells can be achieved either via direct interactions or via secretion of soluble factors. The emergence of extracellular vesicles (EVs) as entities that play key roles in cell-to-cell communication offer opportunities in exploring their features for use in therapeutics; i.e., management and treatment of various pathologies, such as those used for cancer. The potential use of EVs as therapeutic agents is attributed not only for their cell membrane-bound components, but also for their cargos, mostly bioactive molecules, wherein the former regulate interactions with a recipient cell while the latter trigger cellular functions/molecular mechanisms of a recipient cell. In this article, we highlight the involvement of EVs in hallmarks of a cancer cell, particularly focusing on those molecular processes that are influenced by EV cargos. Moreover, we explored the roles of RNA species and proteins carried by EVs in eliciting drug resistance phenotypes. Interestingly, engineered EVs have been investigated and proposed as therapeutic agents in various in vivo and in vitro studies, as well as in several clinical trials.

scholarly journals Aldehyde Dehydrogenases: Not Just Markers, but Functional Regulators of Stem Cells

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Giuseppe Vassalli
Keyword(s):  
Stem Cells ◽  
Molecular Mechanisms ◽  
Cell Types ◽  
Cellular Function ◽  
Stem Cell Marker ◽  
Cell Populations ◽  
Aldh Activity ◽  
Cellular Functions ◽  
Stem And Progenitor Cells

Aldehyde dehydrogenase (ALDH) is a superfamily of enzymes that detoxify a variety of endogenous and exogenous aldehydes and are required for the biosynthesis of retinoic acid (RA) and other molecular regulators of cellular function. Over the past decade, high ALDH activity has been increasingly used as a selectable marker for normal cell populations enriched in stem and progenitor cells, as well as for cell populations from cancer tissues enriched in tumor-initiating stem-like cells. Mounting evidence suggests that ALDH not only may be used as a marker for stem cells but also may well regulate cellular functions related to self-renewal, expansion, differentiation, and resistance to drugs and radiation. ALDH exerts its functional actions partly through RA biosynthesis, as all-trans RA reverses the functional effects of pharmacological inhibition or genetic suppression of ALDH activity in many cell types in vitro. There is substantial evidence to suggest that the role of ALDH as a stem cell marker comes down to the specific isoform(s) expressed in a particular tissue. Much emphasis has been placed on the ALDH1A1 and ALDH1A3 members of the ALDH1 family of cytosolic enzymes required for RA biosynthesis. ALDH1A1 and ALDH1A3 regulate cellular function in both normal stem cells and tumor-initiating stem-like cells, promoting tumor growth and resistance to drugs and radiation. An improved understanding of the molecular mechanisms by which ALDH regulates cellular function will likely open new avenues in many fields, especially in tissue regeneration and oncology.

scholarly journals DNA polymerase iota and related Rad30–like enzymes

2001 ◽  
Vol 356 (1405) ◽  
pp. 53-60 ◽  
Author(s):  
John P. McDonald ◽  
Agnès Tissier ◽  
Ekaterina G. Frank ◽  
Shigenori Iwai ◽  
Fumio Hanaoka ◽  
...  
Keyword(s):  
Dna Polymerase ◽  
Xeroderma Pigmentosum ◽  
Molecular Mechanisms ◽  
Dna Polymerases ◽  
Cellular Functions ◽  
Translesion Dna Synthesis ◽  
Dna Polymerase Iota ◽  
Biochemical Studies ◽  
Template Dna

Until recently, the molecular mechanisms of translesion DNA synthesis (TLS), a process whereby a damaged base is used as a template for continued replication, was poorly understood. This area of scientific research has, however, been revolutionized by the finding that proteins long implicated in TLS are, in fact, DNA polymerases. Members of this so–called UmuC/DinB/Rev1/Rad30 superfamily of polymerases have been identified in prokaryotes, eukaryotes and archaea. Biochemical studies with the highly purified polymerases reveal that some, but not all, can traverse blocking lesions in template DNA. All of them share a common feature, however, in that they exhibit low fidelity when replicating undamaged DNA. Of particular interest to us is the Rad30 subfamily of polymerases found exclusively in eukaryotes. Humans possess two Rad30 paralogs, Rad30A and Rad30B. The RAD30A gene encodes DNA polymerase η and defects in the protein lead to the xeroderma pigmentosum variant (XP–V) phenotype in humans. Very recently RAD30B has also been shown to encode a novel DNA polymerase, designated as Pol ι. Based upon in vitro studies, it appears that Pol ι has the lowest fidelity of any eukaryotic polymerase studied to date and we speculate as to the possible cellular functions of such a remarkably error–prone DNA polymerase.

scholarly journals Myosin 1b Flattens and Prunes Branched Actin Filaments

2020 ◽  
Author(s):  
Julien Pernier ◽  
Antoine Morchain ◽  
Valentina Caorsi ◽  
Aurélie Bertin ◽  
Hugo Bousquet ◽  
...  
Keyword(s):  
Total Internal Reflection ◽  
Molecular Motor ◽  
Internal Reflection ◽  
Total Internal Reflection Fluorescence ◽  
Actin Network ◽  
Tirf Microscopy ◽  
Actin Networks ◽  
Cellular Processes

AbstractMotile and morphological cellular processes require a spatially and temporally coordinated branched actin network that is controlled by the activity of various regulatory proteins including the Arp2/3 complex, profilin, cofilin and tropomyosin. We have previously reported that myosin 1b regulates the density of the actin network in the growth cone. Using in vitro F-actin gliding assays and total internal reflection fluorescence (TIRF) microscopy we show in this report that this molecular motor flattens the Arp2/3-dependent actin branches up to breaking them and reduces the probability to form new branches. This experiment reveals that myosin 1b can produce force sufficient enough to break up the Arp2/3-mediated actin junction. Together with the former in vivo studies, this work emphasizes the essential role played by myosins in the architecture and in the dynamics of actin networks in different cellular regions.Short summaryUsing in vitro F-actin gliding assays and total internal reflection fluorescence (TIRF) microscopy we show that myosin flattens the Arp2/3-dependent actin branches up to breaking them and reduces the probability to form new branches

scholarly journals Synergy between Cyclase-associated protein and Cofilin accelerates actin filament depolymerization by two orders of magnitude

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Shashank Shekhar ◽  
Johnson Chung ◽  
Jane Kondev ◽  
Jeff Gelles ◽  
Bruce L. Goode
Keyword(s):  
Actin Filament ◽  
Single Molecule ◽  
Actin Filaments ◽  
Binding Protein ◽  
Actin Dynamics ◽  
Actin Network ◽  
Cellular Mechanisms ◽  
Actin Networks ◽  
Binding Event

AbstractCellular actin networks can be rapidly disassembled and remodeled in a few seconds, yet in vitro actin filaments depolymerize slowly over minutes. The cellular mechanisms enabling actin to depolymerize this fast have so far remained obscure. Using microfluidics-assisted TIRF, we show that Cyclase-associated protein (CAP) and Cofilin synergize to processively depolymerize actin filament pointed ends at a rate 330-fold faster than spontaneous depolymerization. Single molecule imaging further reveals that hexameric CAP molecules interact with the pointed ends of Cofilin-decorated filaments for several seconds at a time, removing approximately 100 actin subunits per binding event. These findings establish a paradigm, in which a filament end-binding protein and a side-binding protein work in concert to control actin dynamics, and help explain how rapid actin network depolymerization is achieved in cells.

DIFFERENTIAL STABILITY OF IODINE POOR AND IODINE RICH RAT THYROGLOBULIN

1974 ◽  
Vol 75 (1) ◽  
pp. 33-49 ◽  
Author(s):  
Lubomir J. Valenta
Keyword(s):  
Ionic Strength ◽  
Succinic Anhydride ◽  
Iodine Concentration ◽  
Freezing And Thawing ◽  
Sedimentation Pattern ◽  
Differential Stability ◽  
Chaotropic Anions ◽  
Low Ionic Strength ◽  
Covalent Interactions

ABSTRACT In certain environments thyroglobulin is dissociated into 12S subunit or unfolded into 14–17S species. The unfolding and dissociating ability of various agents was examined on poorly iodinated (PIT) or iodine rich (IRT) rat thyroglobulins. According to the efficiency of provoking unfolding or dissociation these agents could be grouped in the following order: low ionic strength < chaotropic anions < chaotropic anions plus freezing and thawing < succinic anhydride and mild alkali < SDS < strong alkali. The degree of thyroglobulin changes was further dependent on the iodine concentration. No change of sedimentation pattern was obtained in the presence of 2-mercaptoethanol or after incomplete reduction and alkylation of the iodine rich protein. No stabilization of PIT was brought about by a number of oxidizing agents. Stabilization was only obtained by in vitro iodination. The main difference between the uneffected and unfolded or dissociated thyroglobulin species was in the amount of thyroxine, or, at lower levels of iodination, DIT. The results suggest that non-covalent, especially hydrophobic, rather than covalent interactions are involved in stabilization of conformation of the thyroglobulin molecule.

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