dictyNews Electronic Edition Volume 42, number 11 April 15, 2016 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. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= 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 [masahiroueda@fbs.osaka-u.ac.jp] ——————————————————————————————————————— 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 [ludwig.eichinger@uni-koeln.de] ============================================================== [End dictyNews, volume 42, number 11]