Estrutura tridimensional do flagelo/cília eucariótico por tomografia crio-eletrônica: mero acaso, fortuita necessidade ou design inteligente?

segunda-feira, novembro 20, 2017

BIOPHYSICS

Vol. 9 (2013) p. 141-148

DOI: http://doi.org/10.2142/biophysics.9.141

Review Article

3D structure of eukaryotic flagella/cilia by cryo-electron tomography



Takashi Ishikawa1)

1) Laboratory of Biomolecular Research, Paul Scherrer Institute, Villigen PSI

Released on J-STAGE 2013/10/17 

Received 2013/07/09 Accepted 2013/09/25

Keywords: dynein, microtubule, cryo-EM, axoneme, motor protein

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Ajuste fino de cílios e flagelos móveis: a evolução das proteínas do motor de dineína de plantas aos seres humanos em alta resolução: mero acaso, fortuita necessidade ou design inteligente?

Fine-Tuning Motile Cilia and Flagella: Evolution of the Dynein Motor Proteins from Plants to Humans at High Resolution 

Martin Kollmar

Molecular Biology and Evolution, Volume 33, Issue 12, 1 December 2016, Pages 3249–3267, https://doi.org/10.1093/molbev/msw213

Published: 07 October 2016


Abstract

The flagellum is a key innovation linked to eukaryogenesis. It provides motility by regulated cycles of bending and bend propagation, which are thought to be controlled by a complex arrangement of seven distinct dyneins in repeated patterns of outer- (OAD) and inner-arm dynein (IAD) complexes. Electron tomography showed high similarity of this axonemal repeat pattern across ciliates, algae, and animals, but the diversity of dynein sequences across the eukaryotes has not yet comprehensively been resolved and correlated with structural data. To shed light on the evolution of the axoneme I performed an exhaustive analysis of dyneins using the available sequenced genome data. Evidence from motor domain phylogeny allowed expanding the current set of nine dynein subtypes by eight additional isoforms with, however, restricted taxonomic distributions. I confirmed the presence of the nine dyneins in all eukaryotic super-groups indicating their origin predating the last eukaryotic common ancestor. The comparison of the N-terminal tail domains revealed a most likely axonemal dynein origin of the new classes, a group of chimeric dyneins in plants/algae and Stramenopiles, and the unique domain architecture and origin of the outermost OADs present in green algae and ciliates but not animals. The correlation of sequence and structural data suggests the single-headed class-8 and class-9 dyneins to localize to the distal end of the axonemal repeat and the class-7 dyneins filling the region up to the proximal heterodimeric IAD. Tracing dynein gene duplications across the eukaryotes indicated ongoing diversification and fine-tuning of flagellar functions in extant taxa and species.

axoneme, cilium, flagellum, dynein, last eukaryotic common ancestor.

Issue Section: Discoveries

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A tomografia crio-eletrônica revela características conservadas de microtúbulos duplos em flagelos: mero acaso, fortuita necessidade ou design inteligente?

Cryo-electron tomography reveals conserved features of doublet microtubules in flagella

Daniela Nicastro a,1, Xiaofeng Fu a,b, Thomas Heuser a, Alan Tso a, Mary E. Porter c, and Richard W. Linck c 

Author Affiliations

Edited by J. Richard McIntosh, University of Colorado, Boulder, CO, and approved August 24, 2011 (received for review May 3, 2011)

Fig. 1. Cryo-ET provides an overview of the 3D structure of DMTs. Tomographic slices (A and B) and isosurface renderings (D–F) of averaged axonemal repeats from Chlamydomonas pseudo-WT (pWT; Table 1) show cross-sectional (A and D), longitudinal (B), and oblique (E and F) views of the DMT. The red lines in A indicate the cutting plane of the slice shown in B. In the surface renderings, only the DMT core is shown, whereas all peripheral structures [e.g., inner or outer dynein arm (IDA or ODA, respectively)] were removed but their positions are indicated in A (surface rendering overview with associated structures is shown in Fig. S1). PF numbers [according to Linck and Stephens (16)] are colored pink in the A-tubule (At) and dark blue in the B-tubule (Bt). In B, prominent left-handed helical lines with an 8-nm axial periodicity are apparent, probably corresponding to the helical lattice of tubulin subunits (28, 49). The IJ and trimeric outer junction (OJ) have distinct structures. Colored arrowheads point to MIP1 (light blue), MIP2 (red), MIP3 (yellow), and MIP4 (orange). DMT cross-sections are viewed from a proximal orientation (flagellar base) toward a distal (flagellar tip) orientation, and in the longitudinal view, the left side is proximal. The DMT orientations, labels, and colors shown here are used consistently in all subsequent figures unless otherwise noted and are valid for all panels. (C) Resolution of the DMT averages used in this study ranged from 3.3 to 3.9 nm (0.5 criterion of the Fourier shell correlation method). More details are provided in Table 1. (Scale bar: 10 nm.)

Abstract

The axoneme forms the essential and conserved core of cilia and flagella. We have used cryo-electron tomography of Chlamydomonas and sea urchin flagella to answer long-standing questions and to provide information about the structure of axonemal doublet microtubules (DMTs). Solving an ongoing controversy, we show that B-tubules of DMTs contain exactly 10 protofilaments (PFs) and that the inner junction (IJ) and outer junction between the A- and B-tubules are fundamentally different. The outer junction, crucial for the initiation of doublet formation, appears to be formed by close interactions between the tubulin subunits of three PFs with unusual tubulin interfaces; other investigators have reported that this junction is weakened by mutations affecting posttranslational modifications of tubulin. The IJ consists of an axially periodic ladder-like structure connecting tubulin PFs of the A- and B-tubules. The recently discovered microtubule inner proteins (MIPs) on the inside of the A- and B-tubules are more complex than previously thought. They are composed of alternating small and large subunits with periodicities of 16 and/or 48 nm. MIP3 forms arches connecting B-tubule PFs, contrary to an earlier report that MIP3 forms the IJ. Finally, the “beak” structures within the B-tubules of Chlamydomonas DMT1, DMT5, and DMT6 are clearly composed of a longitudinal band of proteins repeating with a periodicity of 16 nm. These findings, discussed in relation to genetic and biochemical data, provide a critical foundation for future work on the molecular assembly and stability of the axoneme, as well as its function in motility and sensory transduction.

microtubule stability cilia axoneme ciliopathies cytoskeleton

Footnotes

1To whom correspondence should be addressed. E-mail: nicastro@brandeis.edu.

Author contributions: D.N. designed research; D.N., X.F., T.H., and A.T. performed research; M.E.P. contributed new reagents/analytic tools; D.N., X.F., T.H., and R.W.L. analyzed data; and D.N. and R.W.L. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

See Author Summary on page 17249.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1106178108/-/DCSupplemental.

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Análise estrutural tridimensional de flagelo/cilia eucariótico por tomografia eletro-crio.

J. Synchrotron Rad. (2011). 18, 2-5

Three-dimensional structural analysis of eukaryotic flagella/cilia by electron cryo-tomography


K. H. Bui, G. Pigino and T. Ishikawa


Figure 1 Structure of a flagellum and its components in various dimensions. The appropriate method for structural analysis at each scale is shown on the right. (a) Chlamydomonas cell with two flagella (5–10 µm length, 0.25 µm diameter). (b) Cross section [at the red dotted circle in (a)] of a flagellum. ODA: outer dynein arms. IDA: inner dynein arms. RS: radial spokes. (c) One microtubule doublet is extracted [red dotted circle in (b)], rotated and enlarged. (d) Schematic diagram of one dynein heavy chain [enclosed by the red dotted line in (c)]. (e) Atomic structure of the microtubule binding domain at the tip of the coiled-coil stalk.

Abstract

Electron cryo-tomography is a potential approach to analyzing the three-dimensional conformation of frozen hydrated biological macromolecules using electron microscopy. Since projections of each individual object illuminated from different orientations are merged, electron tomography is capable of structural analysis of such heterogeneous environments as in vivo or with polymorphism, although radiation damage and the missing wedge are severe problems. Here, recent results on the structure of eukaryotic flagella, which is an ATP-driven bending organelle, from green algae Chlamydomonas are presented. Tomographic analysis reveals asymmetric molecular arrangements, especially that of the dynein motor proteins, in flagella, giving insight into the mechanism of planar asymmetric bending motion. Methodological challenges to obtaining higher-resolution structures from this technique are also discussed.

Keywords: dynein; flagella; axoneme; tomography; cryo-EM.

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Foi a evolução pulsada que modelou os tamanhos dos planos corporais dos vertebrados

Pulsed evolution shaped modern vertebrate body sizes

Michael J. Landis a and Joshua G. Schraiber b,c,

Author Affiliations

Edited by Neil H. Shubin, The University of Chicago, Chicago, IL, and approved October 6, 2017 (received for review June 18, 2017)


Fig. 1.
Model selection profiles for 66 vertebrate clades. Clade colors indicate their order: black, fish; purple, amphibians; green, reptiles; blue, birds; and red, mammals. Each clade was fitted to seven models, classified into four groups: incremental change (BM), incremental stationarity (OU), explosive change (EB), and pulsed change (JN, NIG, BM+JN, BM+NIG). AICc weights were computed using only the best-fitting model within each class. A model class is selected only if its AICc weight is twice as large than that of any other model class (circles indicate selection counts: 12 incremental change, 1 incremental stationarity, 9 explosive change, 21 pulsed change, 23 ambiguous). Alternative model classifications are provided in SI Appendix.

Significance

The diversity of forms found among animals on Earth is striking. Despite decades of study, it has been difficult to reconcile the patterns of diversity seen between closely related species with those observed when studying single species on ecological timescales. We propose a set of models, called Lévy processes, to attempt to reconcile rapid evolution between species with the relatively stable distributions of phenotypes seen within species. These models, which have been successfully used to model stock market data, allow for long periods of stasis followed by bursts of rapid change. We find that many vertebrate groups are well fitted by Lévy models compared with models for which traits evolve toward a stationary optimum or evolve in an incremental and wandering manner.

Abstract

The relative importance of different modes of evolution in shaping phenotypic diversity remains a hotly debated question. Fossil data suggest that stasis may be a common mode of evolution, while modern data suggest some lineages experience very fast rates of evolution. One way to reconcile these observations is to imagine that evolution proceeds in pulses, rather than in increments, on geological timescales. To test this hypothesis, we developed a maximum-likelihood framework for fitting Lévy processes to comparative morphological data. This class of stochastic processes includes both an incremental and a pulsed component. We found that a plurality of modern vertebrate clades examined are best fitted by pulsed processes over models of incremental change, stationarity, and adaptive radiation. When we compare our results to theoretical expectations of the rate and speed of regime shifts for models that detail fitness landscape dynamics, we find that our quantitative results are broadly compatible with both microevolutionary models and observations from the fossil record.

macroevolution Levy process pulsed evolution adaptive landscape

Footnotes

1To whom correspondence should be addressed. Email: joshua.schraiber@temple.edu.

Author contributions: M.J.L. and J.G.S. designed research, performed research, analyzed data, and wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1710920114/-/DCSupplemental.

Copyright © 2017 the Author(s). Published by PNAS.

This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).


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Delimitando a velocidade da gravidade com as observações de ondas gravitacionais

Bounding the Speed of Gravity with Gravitational Wave Observations

Neil Cornish, Diego Blas, and Germano Nardini
Phys. Rev. Lett. 119, 161102 – Published 18 October 2017



Abstract

The time delay between gravitational wave signals arriving at widely separated detectors can be used to place upper and lower bounds on the speed of gravitational wave propagation. Using a Bayesian approach that combines the first three gravitational wave detections reported by the LIGO Scientific and Virgo Collaborations we constrain the gravitational waves propagation speed 
cgw
 to the 90% credible interval 
0.55c<cgw<1.42c
, where 
c
 is the speed of light in vacuum. These bounds will improve as more detections are made and as more detectors join the worldwide network. Of order 20 detections by the two LIGO detectors will constrain the speed of gravity to within 20% of the speed of light, while just five detections by the LIGO-Virgo-Kagra network will constrain the speed of gravity to within 1% of the speed of light.

Received 19 July 2017



Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)
Research Areas
Alternative gravity theories Gravitational waves Gravitation, Cosmology & Astrophysics

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Só a Nomenklatura científica e a Galera dos meninos e meninas de Darwin acreditam no mito da ciência se corrigir a si mesma!

sábado, novembro 18, 2017

Correcting the “self-correcting” mythos of science

Douglas Allchin *

Source/Fonte: PLoS Blog


Abstract: 

In standard characterizations, science is self-correcting. Scientists examine each other’s work skeptically, try to replicate important discoveries, and thereby expose latent errors. Thus, while science is tentative, it also seems to have a system for correcting whatever mistakes arise. It powerfully explains and justifies the authority of science. Self-correction thus often serves emblematically in promoting science as a superior form of knowledge. But errors can and do occur. Some errors remain uncorrected for long periods. I present five sets of historical observations that indicate a need to rethink the widespread mythos of self-correction. First, some errors persist for decades, wholly undetected. Second, many errors seem corrected by independent happenstance, not by any methodical appraisal. Third, some errors have been “corrected” in a cascade of successive errors that did not effectively remedy the ultimate source of the error. Fourth, some errors have fostered further serious errors without the first error being noticed. Finally, some corrections to erroneous theories have themselves been rejected when initially presented. In all these cases, scientists failed to identify and correct the errors in a timely manner, or according to any uniform self-correcting mechanism. These historical perspectives underscore that error correction in science requires epistemic work. We need deeper understanding of errors, through the emerging field of error analytics.

Keywords: scientific error; self-correction; error cascade; compounded error; error analytics


* The Minnesota Center for the Philosophy of Science and STEM Education Center.
University of Minnesota, Minneapolis, MN, U.S.A, ZIP 55455. 
E-mail: allch001@umn.edu

Custo mutagênico de ribonucleotídeos no DNA bacteriano

sexta-feira, novembro 17, 2017

Mutagenic cost of ribonucleotides in bacterial DNA

Jeremy W. Schroeder a,1,2, Justin R. Randall a,1, William G. Hirst a, Michael E. O’Donnell b,3, and Lyle A. Simmons a,

Author Affiliations

Contributed by Michael E. O’Donnell, September 18, 2017 (sent for review June 19, 2017; reviewed by Martin Marinus and Roger Woodgate)



Significance

DNA polymerases frequently incorporate ribonucleotides in place of deoxyribonucleotides during genome replication. RNase HII is responsible for initiating the removal of ribonucleotide errors across all three domains of life. Ribonucleotides that persist in genomic DNA due to defects in RNase HII result in strand breaks, mutagenesis, and neurodevelopmental disease in humans. Here, we define the proteins important for ribonucleotide excision repair in Bacillus subtilis and use genome-wide mutational profiling to determine the mutagenic cost of ribonucleotides in RNase HII-deficient cells. We show that the absence of RNase HII yields error-prone ribonucleotide correction via a pathway that relies on an essential DNA polymerase. We further demonstrate that error-prone ribonucleotide removal causes sequence context-dependent GC → AT transitions on the lagging strand.

Abstract

Replicative DNA polymerases misincorporate ribonucleoside triphosphates (rNTPs) into DNA approximately once every 2,000 base pairs synthesized. Ribonucleotide excision repair (RER) removes ribonucleoside monophosphates (rNMPs) from genomic DNA, replacing the error with the appropriate deoxyribonucleoside triphosphate (dNTP). Ribonucleotides represent a major threat to genome integrity with the potential to cause strand breaks. Furthermore, it has been shown in the bacterium Bacillus subtilis that loss of RER increases spontaneous mutagenesis. Despite the high rNTP error rate and the effect on genome integrity, the mechanism underlying mutagenesis in RER-deficient bacterial cells remains unknown. We performed mutation accumulation lines and genome-wide mutational profiling of B. subtilis lacking RNase HII, the enzyme that incises at single rNMP residues initiating RER. We show that loss of RER in B. subtilis causes strand- and sequence-context–dependent GC → AT transitions. Using purified proteins, we show that the replicative polymerase DnaE is mutagenic within the sequence context identified in RER-deficient cells. We also found that DnaE does not perform strand displacement synthesis. Given the use of nucleotide excision repair (NER) as a backup pathway for RER in RNase HII-deficient cells and the known mutagenic profile of DnaE, we propose that misincorporated ribonucleotides are removed by NER followed by error-prone resynthesis with DnaE.

ribonucleotide excision repair DNA polymerase mutagenesis RNase HII

Footnotes

1J.W.S. and J.R.R. contributed equally to this work.

2Present address: Department of Bacteriology, University of Wisconsin, Madison, WI 53706.

3To whom correspondence may be addressed. Email: odonnel@mail.rockefeller.edu or lasimm@umich.edu.

Author contributions: J.W.S., J.R.R., W.G.H., and L.A.S. designed research; J.W.S., J.R.R., W.G.H., and L.A.S. performed research; J.W.S. and J.R.R. contributed new reagents/analytic tools; J.W.S., J.R.R., W.G.H., M.E.O., and L.A.S. analyzed data; and J.W.S., J.R.R., M.E.O., and L.A.S. wrote the paper.

Reviewers: M.M., University of Massachusetts Medical School; and R.W., National Institute of Child Health and Human Development, National Institutes of Health.

The authors declare no conflict of interest.

Data deposition: The sequences reported in this paper have been deposited in the Sequence Read Archive database (accession no. SRP117359).

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1710995114/-/DCSupplemental.

Copyright © 2017 the Author(s). Published by PNAS.

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A evolução heterocrônica explica o novo formato corporal de um celacanto do Triássico da Suiça

Heterochronic evolution explains novel body shape in a Triassic coelacanth from Switzerland

Lionel Cavin, Bastien Mennecart, Christian Obrist, Loïc Costeur & Heinz Furrer

Scientific Reports 7, Article number: 13695 (2017)


Download Citation

Embryonic induction Evolution Ichthyology Palaeontology

Received: 05 June 2017 Accepted: 02 October 2017

Published online: 20 October 2017



Phylogenetic relationships of Foreyia maxkuhni gen. et sp. nov. and developmental origin of the derived characters.

Abstract

A bizarre latimeriid coelacanth fish from the Middle Triassic of Switzerland shows skeletal features deviating from the uniform anatomy of coelacanths. The new form is closely related to a modern-looking coelacanth found in the same locality and differences between both are attributed to heterochronic evolution. Most of the modified osteological structures in the new coelacanth have their developmental origin in the skull/trunk interface region in the embryo. Change in the expression of developmental patterning genes, specifically the Pax1/9 genes, may explain a rapid evolution at the origin of the new coelacanth. This species broadens the morphological disparity range within the lineage of these ‘living fossils’ and exemplifies a case of rapid heterochronic evolution likely trigged by minor changes in gene expression.

Acknowledgements

The Palaeontological Institute and Museum, University of Zürich (PIMUZ) enabled H.F. to conduct systematic prospecting and numerous excavations near Davos. The government of Canton Graubünden, the municipality of Davos, and the Bündner Naturmuseum in Chur gave permission for the excavations and financial support. Max Kuhn (Uster) provided generous financial support for the preparation of the specimens by C.O. B.M. and L.Ca. also thank the Département de la culture et du sport de la Ville de Genève for a financial support for computer facilities, and Philippe Wagneur (Natural History Museum of Geneva) for assistance to produce the CT scan movie. We thank Anne Kemp (Griffith University) and Mélanie Debiais-Thibaud (University of Montpellier) for discussion. This paper is a contribution to the project “Evolutionary pace in the coelacanth clade: New evidence from the Triassic of Switzerland” supported by the Swiss National Science Foundation (200021-172700) by L.Ca.

Author information

Affiliations

Department of Geology and Palaeontology, Muséum d’Histoire Naturelle, CP6434, 1211, Geneva, 6, Switzerland

Lionel Cavin

Naturhistorisches Museum Basel, Augustinergasse 2, 4001, Basel, Switzerland

Bastien Mennecart & Loïc Costeur

Erliackerweg 8, 4462, Rickenbach, BL, Switzerland

Christian Obrist

Paläontologisches Institut und Museum der Universität Zürich, Karl Schmid-Strasse 4, 8006, Zurich, Switzerland

Heinz Furrer

Contributions

L.Ca. wrote the description of the new taxon, collected and analyzed the phylogenetic and ontogenetic data, and wrote the corresponding parts of the manuscript. C.O. collected specimens PIMUZ A/I 4620 and PIMUZ A/I 4372, and prepared them. H.F. analyzed the stratigraphic data in the field, and wrote the corresponding methods and results. B.M. and L.Co. performed the CT scan analysis and interpreted the images. L.Ca. and H.F. obtained funding for fieldwork and data analysis. All authors contributed to write the last version of the text.

Competing Interests

The authors declare that they have no competing interests.

Corresponding author

Correspondence to Lionel Cavin.

A topologia da novidade e inovação evolucionárias em macroevolução

quinta-feira, novembro 16, 2017

The topology of evolutionary novelty and innovation in macroevolution

Douglas H. Erwin

Published 23 October 2017. DOI: 10.1098/rstb.2016.0422


Abstract

Sewall Wright's fitness landscape introduced the concept of evolutionary spaces in 1932. George Gaylord Simpson modified this to an adaptive, phenotypic landscape in 1944 and since then evolutionary spaces have played an important role in evolutionary theory through fitness and adaptive landscapes, phenotypic and functional trait spaces, morphospaces and related concepts. Although the topology of such spaces is highly variable, from locally Euclidean to pre-topological, evolutionary change has often been interpreted as a search through a pre-existing space of possibilities, with novelty arising by accessing previously inaccessible or difficult to reach regions of a space. Here I discuss the nature of evolutionary novelty and innovation within the context of evolutionary spaces, and argue that the primacy of search as a conceptual metaphor ignores the generation of new spaces as well as other changes that have played important evolutionary roles.

This article is part of the themed issue ‘Process and pattern in innovations from cells to societies’.

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Principais transições na evolução humana

Major transitions in human evolution

Robert A. Foley, Lawrence Martin, Marta Mirazón Lahr, Chris Stringer

Published 13 June 2016.DOI: 10.1098/rstb.2015.0229


Abstract

Evolutionary problems are often considered in terms of ‘origins', and research in human evolution seen as a search for human origins. However, evolution, including human evolution, is a process of transitions from one state to another, and so questions are best put in terms of understanding the nature of those transitions. This paper discusses how the contributions to the themed issue ‘Major transitions in human evolution’ throw light on the pattern of change in hominin evolution. Four questions are addressed: (1) Is there a major divide between early (australopithecine) and later (Homo) evolution? (2) Does the pattern of change fit a model of short transformations, or gradual evolution? (3) Why is the role of Africa so prominent? (4) How are different aspects of adaptation—genes, phenotypes and behaviour—integrated across the transitions? The importance of developing technologies and approaches and the enduring role of fieldwork are emphasized.

This article is part of the themed issue ‘Major transitions in human evolution’.

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Máquinas mitocondriais para importação e montagem de proteínas: mero acaso, fortuita necessidade ou design inteligente?

Annu. Rev. Biochem. 2017. 86:685–714

First published as a Review in Advance on March 15, 2017

The Annual Review of Biochemistry is online at biochem.annualreviews.org


Mitochondrial Machineries for Protein Import and Assembly

Nils Wiedemann and Nikolaus Pfanner

Institute of Biochemistry and Molecular Biology, ZBMZ, Faculty of Medicine, and BIOSS

Centre for Biological Signaling Studies, University of Freiburg, 79104 Freiburg, Germany;

email:nils.wiedemann@biochemie.uni-freiburg.de, nikolaus.pfanner@biochemie.uni-freiburg.de

Keywords

preprotein, protein sorting, translocase, outer membrane, inner membrane, mitochondrial architecture


Abstract

Mitochondria are essential organelles with numerous functions in cellular metabolism and homeostasis. Most of the >1,000 different mitochondrial proteins are synthesized as precursors in the cytosol and are imported into mitochondria by five transport pathways. The protein import machineries of the mitochondrial membranes and aqueous compartments reveal a remarkable variability of mechanisms for protein recognition, translocation, and sorting. The protein translocases do not operate as separate entities but are connected to each other and to machineries with functions in energetics, membrane organization, and quality control. Here, we discuss the versatility and dynamic organization of the mitochondrial protein import machineries. Elucidating the molecular mechanisms of mitochondrial protein translocation is crucial for understanding the integration of protein translocases into a large network that controls organelle biogenesis, function, and dynamics.

Copyright © 2017 Wiedemann & Pfanner.

This work is licensed under a Creative Commons Attribution 4.0 International License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. See credit lines of images or other third party material in this article for license information.

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O sistema de coagulação sanguínea como uma máquina molecular: mero acaso, fortuita necessidade ou design inteligente?

The blood coagulation system as a molecular machine

Authors: Henri M.H. Spronk, José W.P. Govers-Riemslag, Hugo ten Cate

First published: 17 November 2003 Full publication history



Abstract

The human blood coagulation system comprises a series of linked glycoproteins that upon activation induce the generation of downstream enzymes ultimately forming fibrin. This process is primarily important to arrest bleeding (hemostasis). Hemostasis is a typical example of a molecular machine, where the assembly of substrates, enzymes, protein cofactors and calcium ions on a phospholipid surface markedly accelerates the rate of coagulation. Excess, pathological, coagulation activity occurs in “thrombosis”, the formation of an intravascular clot, which in the most dramatic form precipitates in the microvasculature as disseminated intravascular coagulation. Thrombosis occurs according to a biochemical machine model in the case of atherothrombosis on a ruptured atherosclerotic plaque, but may develop at a slower rate in venous thrombosis, illustrating that the coagulation machinery can act at different velocities. The separate coagulation enzymes are also important in other biological processes, including inflammation for which the rapid conversion of one coagulation factor by the other is not a prerequisite. The latter role of coagulation enzymes may be related to the old and probably maintained function of the coagulation machine in innate immunity. 

BioEssays 25:1220–1228, 2003. © 2003 Wiley Perioicals, Inc.

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Dinâmica da estrutura cromossômica durante o ciclo celular: mero acaso, fortuita necessidade ou design inteligente?

Chromosome structure dynamics during the cell cycle: a structure to fit every phase

Authors: Christopher Barrington, Dubravka Pezic, Suzana Hadjur

First published: 4 September 2017Full publication history


See also: L Lazar-Stefanita et al (September 2017) Y Kakui et al (2017),

SA Schalbetter et al (September 2017), T Nagano et al (July 2017)


Figure 1. Chromosome structures and SMC proteins during the cell cycle

Abstract

Chromosomes undergo dramatic morphological changes as cells advance through the cell cycle. Using powerful molecular and computational methods, several recent studies revealed an outstanding complexity of continuous structural changes accompanying cell cycle progression. In agreement with cell division being a fundamental cellular process, characteristic features of cell cycle stage-specific genome structure are conserved from yeast to mouse. These studies further shine light on the critical roles that SMC complexes, already well known as fundamental regulators of chromosome topology, have in orchestrating structural dynamics throughout the cell cycle.

Molecular methods such as Hi-C measure physical contacts between DNA fragments in an unbiased and genome-wide manner (Lieberman Aiden et al, 2009), permitting researchers to describe the higher-order folding principles of chromosomes with great resolution and in a high throughput manner (Dixon et al, 2012; Nora et al, 2012; Sexton et al, 2012). Four recent studies have harnessed the power of Hi-C and its statistical analyses to further our understanding of the dramatic structural changes that occur within chromosomes during cell cycle progression. Collectively, the work in Schizosaccharomyces pombe (Kakui et al, 2017), Saccharomyces cerevisiae (Lazar-Stefanita et al, 2017; Schalbetter et al, 2017) and mouse ES cells (Nagano et al, 2017) has revealed distinct cell cycle stage chromosome structures, the importance of structural maintenance of chromosome (SMC) proteins throughout this process and the conservation of structural features between species.

FREE PDF GRATIS: The EMBO Journal

I Simpósio de Design Inteligente do Nordeste - 10-11 Nov 2017 Fac. Direito - UFC

quarta-feira, novembro 08, 2017



I Simpósio de Design Inteligente do Nordeste

TDI NORDESTE

Sexta-feira, 10 de novembro de 2017 às 19:00 - Sábado, 11 de novembro de 2017 às 19:00 (Horário Padrão de Brasília Horário Brasil (Fortaleza))

Fortaleza, CE

Detalhes do evento

Ao longo da História da Ciência a origem do universo e origem da vida tem despertado os mais variados cientistas a pesquisarem as causas e as evidências destes fenômenos. Um grupo de cientistas tem descoberto ao longo do tempo a presença de complexidade e ordem sistêmica presente em organismos microcelulares e indo até a organização do Cosmo. Para que se haja vida humana no planeta, o mesmo apresenta um conjunto de condicionantes denominadas fatores antrópicos que criam um ecossistema favorável a existência e a preservação do Homem. Podemos destacar neste cenário as taxas ideais de oxigênio , o eixo de inclinação da terra permitindo as quatros estações, a distância ideal entre a Terra e o Sol permitindo uma chegada de radiação ideal para a vida, além de um campo magnético ao redor da terra protegendo a crosta terrestre contra excesso de radiação. Venha e participe. Você é nosso convidado. Conheça mais sobre a Teoria do Design Inteligente.

***** PROGRAMAÇÃO *****

Sexta-feira (10 de Novembro)

19h: Abertura (diretores, reitores, organizadores)

19h15min: “Design Inteligente: Ciência ou Religião ?” (Dr. Jonathan Wells)

20h: “Os três pilares da Ciência do Design Inteligente” (Dr. Marcos Eberlin)

20h30min: “Quem é o Designer segundo a boa filosofia e teologia?” (Dr. Glauco Barreira Magalhães Filho)

21h: Perguntas e Respostas

21h45min: Encerramento

Sábado (11 de Novembro)

MANHÃ

9h: “O Código da Vida: Acaso ou Design?” (Ms. Mariana Sá)

9h30min: “A superioridade teórica da TDI” (Ms. Rodolfo Paiva)

10h: “Ideologia naturalista e a intolerância contra a TDI” (Ms. Ricardo Marques)

10h:30min Coffee Break

11h: “As evidências do Design na maquinaria da Vida” (Otângelo Grasso) 

12h30min: Mesa Redonda

TARDE

15h: “20 anos da Complexidade Irredutível: comprovada ou refutada?” (Ms. Douglas Aleodim)

15h30min: “A Ciência e seus pressupostos” (Dr.Tassos Lycurgo)

16h: “Quem veio primeiro: o ovo ou a galinha?” (Dr. Marcos Eberlin)

17h: Coffee Break

17h30min: “Uma breve história da TDI” (Dr. Jonathan Wells)

18h: Mesa Redonda com todos os palestrantes

18h30min: Encerramento

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