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 [log in to unmask]

or by using the form at

http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit.



Back issues of dictyNews, the Dicty Reference database and other

useful information is available at dictyBase - http://dictybase.org.



Follow dictyBase on twitter:

http://twitter.com/dictybase





=========

Abstracts

=========





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 [[log in to unmask]]

———————————————————————————————————————





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 [log in to unmask]]

==============================================================

[End dictyNews, volume 43, number 14]