dictyNews
Electronic Edition
Volume 42, number 11
April 15, 2016

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Abstracts
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Heterotrimeric G protein shuttling via Gip1 extends the dynamic 
range of eukaryotic chemotaxis

Yoichiro Kamimura Yukihiro Miyanaga and Masahiro Ueda 

Laboratory for Cell Signaling Dynamics, Quantitative Biology 
Center (QBiC), RIKEN, Suita, Osaka, 565-0874, Japan.
Laboratory for Single Molecular Biology, Department of Biological 
Sciences, Graduate School of Science, Osaka University, Toyonaka, 
Osaka, 560-0043, Japan.


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

Chemotactic eukaryote cells can sense chemical gradients over 
a wide range of concentrations via heterotrimeric G-protein 
signaling; however, the underlying wide-range sensing mechanisms 
are only partially understood. Here we report that a novel 
regulator of G proteins, G protein-interacting protein 1 (Gip1), 
is essential for extending the chemotactic range of Dictyostelium 
cells. Genetic disruption of Gip1 caused severe defects in gradient 
sensing and directed cell migration at high but not low 
concentrations of chemoattractant. Also, Gip1 was found to bind 
and sequester G proteins in cytosolic pools. Receptor activation 
induced G-protein translocation to the plasma membrane from the 
cytosol in a Gip1-dependent manner, causing a biased redistribution 
of G protein on the membrane along a chemoattractant gradient. 
These findings suggest that Gip1 regulates G-protein shuttling 
between the cytosol and the membrane to ensure the availability 
and biased redistribution of G protein on the membrane for receptor-
mediated chemotactic signaling. This mechanism offers an 
explanation for the wide-range sensing seen in eukaryotic 
chemotaxis.


submitted by: Masahiro Ueda  [[log in to unmask]]
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Mutant p97 exhibits species-specific changes of its ATPase 
activity and compromises the UBXD9-mediated monomerisation 
of p97 hexamers

Ramesh Rijal, Khalid Arhzaouy, Karl-Heinz Strucksberg, 
Megan Cross, Andreas Hofmann, Rolf Schroeder, Christoph S. 
Clemen, Ludwig Eichinger


Eur. J. Cell Biol., in press

p97 (VCP) is a homo-hexameric triple-A ATPase that exerts a plethora 
of cellular processes. Heterozygous missense mu-tations of p97 cause 
at least five human neurodegenerative disorders. However, the 
specific molecular consequences of p97 mutations are hitherto widely 
unknown. Our in silico structural models of human and Dictyostelium 
p97 showed that the disease-causing R93C, R155H, and R155C as well 
as R154C, E219K, R154C/E219K mutations of human and Dic-tyostelium 
p97, respectively, are surface exposed amino acid residues. In-gel p97 
ATPase activity measurements of p97 monomers and hexamers revealed 
significant mutation- and species-specific differences. While all 
human p97 mutations led to an increase in ATPase activity, no changes 
could be detected for the Dictyostelium R154C mutant, which is 
orthol-ogous to human R155C. The E219K mutation led to an almost 
complete loss of activity, which was partially recuperated in the 
R154C/E219K double-mutant indicating p97 inter-domain communication. 
By means of co-immunoprecipitation experiments we identified an 
UBX-domain containing Dictyostelium protein as a novel p97 interaction 
partner. We cate-gorized all UBX-domain containing Dictyostelium 
proteins and named the interaction partner UBXD9. Pull-down assays and 
surface plasmon resonance analyses of Dictyostelium UBXD9 or the human 
orthologue TUG/ASPL/UBXD9 demon-strated direct interactions with p97 
as well as species-, mutation- and ATP-dependent differences in the 
binding affinities. Sucrose density gradients revealed that both human 
and Dictyostelium UBXD9 proteins very efficiently disassembled wild-type, 
but to a lesser extent mutant p97 hexamers into monomers. Our results 
are consistent with a scenario in which p97 point mutations lead to 
differences in enzymatic activities and molecular interactions, which in 
the long-term result in a late-onset and progressive multisystem disease.


submitted by: Ludwig Eichinger [[log in to unmask]]
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[End dictyNews, volume 42, number 11]