dictyNews Volume 24 Number 13

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Dicty News 
Electronic Edition 
Volume 24, number 13 
May 20, 2005 

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

 
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  Abstracts 
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The Diaphanous-related Formin dDia2 is Required for the Formation and  
Maintenance of Filopodia 

Antje Schirenbeck (1), Till Bretschneider (2), Rajesh Arasada (1),  
Michael Schleicher (1), and Jan Faix (1) 

1) A. Butenandt-Institut / Zellbiologie, Ludwig-Maximilians-UniversitŠt,  
Schillerstr. 42, 80336 MŸnchen, Germany. 
2) AG Zelldynamik, Max-Planck-Institut fŸr Biochemie, Am Klopferspitz 18a,  
82152 Martinsried, Germany. 

 
Nature Cell Biology, in press 

Formins play important roles in the nucleation of actin and the formation  
of linear actin filaments, yet their role in filopodium formation has  
remained elusive. Dictyostelium Diaphanous-related formin dDia2 is enriched  
at the tips of filopodia and interacts with profilin II and Rac1. An FH1FH2  
fragment of dDia2 nucleated actin polymerization and removed capping protein  
from capped filament ends. Genetic studies showed that dDia2 is important  
for cell migration as well as the formation, elongation and maintenance of  
filopodia. Here we provide evidence that dDia2 specifically controls  
filopodial dynamics by regulating actin turnover at the barbed ends of  
actin filaments. 

 
Submitted by: Jan Faix [faix@bpc.mh-hannover.de] 

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Biological, Biochemical and Kinetic Effects of Mutations of the 
Cardiomyopathy-loop of Dictyostelium Myosin II: Importance of Ala400 

Xiong Liu*, Shi Shu*, Mih‡ly Kov‡cs , and Edward D. Korn 

Laboratory of Cell Biology, and  Laboratory of Molecular Physiology 
National Heart, Lung, and Blood Institute, National Institutes of Health, 
Bethesda, Maryland 20892 

Running title: Dictyostelium myosin II CM-loop mutants 

Address correspondence to: Edward D. Korn, Laboratory of Cell Biology, 
NHLBI, NIH, Building 50, Room 2517-8017, Bethesda, MD 20892-8017, Tel. 
301-496-1616; Fax. 301-402-1519; E-mail: edk@nih.gov <mailto:edk@nih.gov>  

*XL and SS contributed equally to this work. 

 
Journal of biological Chemistry, in press 
(available on-line May 16th) 

The cardiomyopathy (CM)-loop of the heavy chain of class-II myosins 
begins with a highly conserved Arg residue (whose mutation in human 
beta-cardiac myosin II results in familial hypertrophic cardiomyopathy).  
The CM-loop of Dictyostelium myosin II (R397-Q407) is essential for its 
biological functions and biochemical activities.  We found that the CM-loop 
of smooth muscle myosin II substituted partially and the CM-loop of 
beta-cardiac myosin II much less well for growth, capping of surface receptors 
and development, and the actin-activated MgATPase and in vitro motility 
activities of purified myosins.  There was little correlation between the 
biochemical and biological activities of the two chimeras and 19 point 
mutants but only the five mutants with kcat/Kactin values equivalent to 
wild-type myosin supported essentially full biological function.  The three 
point mutations of R397 equivalent to those that result in hypertrophic 
cardiomyopathy in humans had minimal biological effects and different 
biochemical effects.  The A400V mutation rendered full-length wild-type 
myosin almost completely inactive, both in vitro and in vivo, and the 
reverse V400A mutation in the cardiac CM-loop chimera restored almost full 
activity, even though the sequence still differed from wild-type in 7 of 11 
positions.  Transient kinetic studies of acto-subfragment-1 (S1) showed that 
the chimeras and the Ala/Val, Val/Ala mutations do not affect the 
equilibrium or the association and dissociation rate constants for either 
ATP or ADP binding to acto-S1 or the rate of ATP-induced dissociation of 
acto-S1.   We conclude that the Ala/Val, Val/Ala mutations affect  the 
release of Pi from acto-S1áADPáPi.  In addition, Val at position 400 
substantially reduces the affinity of actin for S1 in the absence of 
nucleotide. 

 
Submitted by: Korn, Edward [korned2@nhlbi.nih.gov] 

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[End Dicty News, volume 24, number 13]