dictyNews Volume 27 Number 06

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dictyNews 
Electronic Edition 
Volume 27, number 6 
August 25, 2006 

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. 

Back issues of dictyNews, the Dicty Reference database and other  
useful information is available at dictyBase - http://dictybase.org. 

 
============= 
  Abstracts 
============= 

 

Phosphorylation of actin Tyr53 inhibits filament nucleation and elongation,  
and destabilizes filaments 

Xiong Liu, Shi Shu, Myoung-Soon S. Hong, Rodney L. Levine*, and  
Edward D. Korn  

Laboratory of Cell Biology, and *Laboratory of Biochemistry, National Heart,  
Lung, and Blood Institute, Bethesda, MD 20892 

 
Proc. Natl. Acad. Sci. USA, in press 

Dictyostelium actin was previously shown to become phosphorylated on Tyr53  
late in the developmental cycle and when cells in the amoeboid stage are  
subjected to stress, but the phosphorylated actin had not been purified and  
characterized.  We have separated phosphorylated and unphosphorylated actin  
and shown that Tyr53-phosphorylation substantially reduces actin's ability  
to inactivate DNase I, increases actin's critical concentration, and greatly  
reduces its rate of polymerization.  Tyr53-phosphorylation substantially, if  
not completely, inhibits nucleation and elongation from the pointed-end of  
actin filaments, and reduces the rate of elongation from the barbed-end.  
Negatively stained electron microscopic images of polymerized  
Tyr53-phosphorylated actin show a variable mixture of small oligomers and  
filaments, which are converted to more typical, long filaments upon addition  
of myosin subfragment 1.  Tyr53-phosphorylated and unphosphorylated actin  
co-polymerize in vitro, and phosphorylated and unphosphorylated actin  
co-localize in amoebae.  Tyr53-phosphorylation does not affect the ability  
of filamentous actin to activate myosin ATPase. 

 
Submitted by: Edward Korn [edk@nih.gov] 
----------------------------------------------------------------------------- 

 
Proteomic fingerprinting of phagosome maturation and evidence for the role  
of a Galpha during uptake 

Daniel Gotthardt1,2*, Vincent Blancheteau3*, Armin Bosserhoff4,  
Thomas Ruppert4, Mauro Delorenzi5,6, and Thierry Soldati1,3,7,# 

*These authors contributed equally to the work 

1)Department of Molecular Cell Research, Max-Planck-Institute for Medical  
Research, D-69120 Heidelberg, Germany. 
2)Department of Internal Medicine IV, University Hospital of Heidelberg,  
D-69120 Heidelberg, Germany. 
3)Department of Biological Sciences, Imperial College, London SW7 2AZ, UK. 
4)Zentrum fŸr Molekulare Biologie der Universitaet Heidelberg (ZMBH),  
D-69120 Heidelberg, Germany. 
5)ISREC National Centre of Competence in Research (NCCR) Molecular Oncology, 
Swiss Institute of Experimental Cancer Research (ISREC), Epalinges,  
Switzerland. 
6)ISREC Swiss Institute of Bioinformatics (SIB), Lausanne, Switzerland. 
7)Department de Biochimie, Faculte des Sciences, Universite de Geneve,  
CH-1211-Geneve-4, Switzerland. 

#)Corresponding author:  
Tel: +41-22-379-6496     Fax: +41-22-379-6470      
E-mail: thierry.soldati@biochem.unige.ch 

 
Molecular Cell Proteomics, in press  
(accessible online at http://www.mcponline.org/papbyrecent.shtml) 

Phagocytosis, whether of food particles in protozoa or bacteria and cell  
remnants in the metazoan immune system, is a conserved process. The  
particles are taken up into phagosomes, which then undergo complex  
remodelling of their components, called maturation. By using 2D gel  
electrophoresis and mass spectrometry, combined with genomic data, we have  
identified 179 phagosomal proteins in the amoeba Dictyostelium, including  
components of signal transduction, membrane traffic and the cytoskeleton.  
By carrying out this proteomic analysis over the course of maturation, we  
obtained time profiles for 1,388 spots and thus generated a dynamic record  
of phagosomal protein composition. Clustering of the time profiles revealed  
five clusters and 24 functional groups that were mapped onto a flow chart  
of maturation. Two heterotrimeric G protein subunits, Galpha4 and Gbeta,  
appeared at the earliest times. We show that mutations in the genes encoding  
these two proteins produce a phagocytic uptake defect in Dictyostelium. This  
analysis of phagosome protein dynamics provides a reference point for future  
genetic and functional investigations. 

 
Submitted by: Thierry Soldati [thierry.soldati@biochem.unige.ch] 
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[End dictyNews, volume 27, number 6]