dictyNews
Electronic Edition
Volume 37, number 5
August 26, 2011

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Abstracts
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Structure, dynamics, lipid-binding, and physiological relevance of 
the putative GTPase-binding domain of Dictyostelium Formin C

Sonja A. Dames 1, Alexander Junemann 2, Hans J. Sass 3, 
André Schönichen 4, Barbara E., Stopschinski 4, Stephan Grzesiek 3, 
Jan Faix 2, and Matthias Geyer 4.

1) Chair of Biomolecular NMR Spectroscopy, Department of Chemistry, 
Technische Universität München, Lichtenbergstr. 4, 85747 Garching, 
Germany; 
2) Institute for Biophysical Chemistry, Hannover Medical School, 
30623 Hannover, Germany; 
3) Department of Structural Biology, Biozentrum, University of Basel, 
Klingelbergstr. 70, 4056 Basel, Switzerland; 
4) Department of Physical Biochemistry, Max-Planck-Institut für 
Molekulare Physiologie, Otto-Hahn-Str. 11, 44227 Dortmund, Germany


J. Biol. Chem., in press

Dictyostelium Formin C (ForC) is involved in the regulation of local 
actin cytoskeleton reorganization, e.g. during cellular adhesion or 
migration. ForC contains formin homology (FH) 2 and 3 domains and an 
N-terminal putative GTPase-binding domain (GBD), but lacks a canonical 
FH1 region. To better understand the role of the GBD, its structure, 
dynamics, lipid-binding properties, and cellular functions were 
analyzed by NMR and CD spectroscopy and by in vivo fluorescence 
microscopy. Moreover, the program CS-Rosetta was tested for the 
structure prediction based on chemical shift data only.

The ForC GBD adopts an ubiquitin-like alpha/beta-roll fold with an 
unusually long loop between beta-strands 1 and 2. Based on the 
lipid-binding data, the presence of DPC micelles induces the formation 
of alpha-helical secondary structure and a rearrangement of the 
tertiary structure. Lipid-binding studies with a mutant protein and 
a peptide suggest that the beta1-beta2-loop is not relevant for these 
conformational changes. Whereas small amounts of negatively charged 
phosphoinositides (PIP45, PIP345) lower the micelle concentration 
necessary to induce the observed spectral changes, other negatively 
charged phospholipids (PS, PG) had no such effect. Interestingly, 
bicelles and micelles composed of diacylphosphocholines had no effect 
on the GBD structure. Our data suggest a model, in which part of the 
large positively charged surface area of the GBD mediates localization 
to specific membrane patches, thereby regulating interactions with 
signaling proteins. Our cellular localization studies show that both, 
the GBD and the FH3 domain, are required for ForC targeting to 
cell-cell contacts and early phagocytic cups and macropinosomes.

Submitted by Jan Faix [[log in to unmask]]
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