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dictyNews Volume 43 Number 14
dictyNews
Electronic Edition
Volume 43, number 14
July 7, 2017
Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to dicty@northwestern.edu
or by using the form at
http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.
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Abstracts
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Drinking problems: mechanisms of macropinosome formation and
maturation.
Catherine M Buckley and Jason S King
Department of Biomedical Sciences, University of Sheffield, UK.
FEBS Journal 2017 May 24
http://onlinelibrary.wiley.com/doi/10.1111/febs.14115/full
Macropinocytosis is a mechanism for the nonspecific bulk uptake
and internalisation of extracellular fluid. This plays specific and
distinct roles in diverse cell types such as macrophages, dendritic
cells and neurons, by allowing cells to sample their environment,
extract extracellular nutrients and regulate plasma membrane
turnover. Macropinocytosis has recently been implicated in
several diseases including cancer, neurodegenerative diseases
and atherosclerosis. Uptake by macropinocytosis is also exploited
by several intracellular pathogens to gain entry into host cells.
Both capturing and subsequently processing large volumes of
extracellular fluid poses a number of unique challenges for the cell.
Macropinosome formation requires coordinated three-dimensional
manipulation of the cytoskeleton to form shaped protrusions able
to entrap extracellular fluid. The following maturation of these large
vesicles then involves a complex series of membrane
rearrangements to shrink and concentrate their contents, while
delivering components required for digestion and recycling.
Recognition of the diverse importance of macropinocytosis in
physiology and disease has prompted a number of recent studies.
In this article, we summarise advances in our understanding of
both macropinosome formation and maturation, and seek to
highlight the important unanswered questions.
submitted by: Jason King [jason.king@sheffield.ac.uk]
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Distinct VASP tetramers synergize in the processive elongation
of individual actin filaments from clustered arrays
Stefan Brühmann1, Dmitry S. Ushakov1, Moritz Winterhoff1,
Richard B. Dickinson2, Ute Curth1, and Jan Faix1
1) Institute for Biophysical Chemistry, Hannover Medical School,
30625 Hannover, Germany;
2) Department of Chemical Engineering, University of Florida,
Gainesville, FL 32611
PNAS, in press
Ena/VASP proteins act as actin polymerases that drive the
processive elongation of filament barbed ends in membrane
protrusions or at the surface of bacterial pathogens. Based on
previous analyses of fast and slow elongating VASP proteins
by in vitro total internal reflection fluorescence microscopy
(TIRFM) and kinetic and thermodynamic measurements, we
established a kinetic model of Ena/VASP-mediated actin
filament elongation. At steady state, it entails that tetrameric
VASP uses one of its arms to processively track growing
filament barbed ends while three G-actin–binding sites
(GABs) on other arms are available to recruit and deliver
monomers to the filament tip, suggesting that VASP
operates as a single tetramer in solution or when clustered
on a surface, albeit processivity and resistance toward
capping protein (CP) differ dramatically between both
conditions. Here, we tested the model by variation of the
oligomerization state and by increase of the number of
GABs on individual polypeptide chains. In excellent
agreement with model predictions, we show that in solution
the rates of filament elongation directly correlate with the
number of free GABs. Strikingly, however, irrespective of the
oligomerization state or presence of additional GABs, filament
elongation on a surface invariably proceeded with the same
rate as with the VASP tetramer, demonstrating that adjacent
VASP molecules synergize in the elongation of a single
filament. Additionally, we reveal that actin ATP hydrolysis is
not required for VASP-mediated filament assembly. Finally,
we show evidence for the requirement of VASP to form
tetramers and provide an amended model of processive
VASPmediated actin assembly in clustered arrays.
submitted by: Jan Faix [faix.jan@mh-hannover.de]
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[End dictyNews, volume 43, number 14]
