The inverse BAR-domain protein IBARa drives membrane remodelling to control osmoregulation, phagocytosis and cytokinesis

Abstract

Here, we analyzed the single inverse Bin/Amphiphysin/Rvs (I-BAR) family member IBARa from Dictyostelium discoideum. The X-ray structure of the N-terminal I-BAR domain solved at 2.2 Å resolution revealed an all-a-helical structure that self-associates into a 165-Å zeppelin-shaped antiparallel dimer. The structural data are consistent with its shape in solution obtained by smallangle X-ray scattering. Cosedimentation, fluorescence anisotropy, and fluorescence and electron microscopy revealed that the I-BAR domain bound preferentially to phosphoinositide-containing vesicles and drove the formation of negatively curved tubules. Immunofluorescence labeling further showed accumulation of endogenous IBARa at the tips of filopodia, the rim of constricting phagocytic cups, in foci connecting dividing cells during the final stage of cytokinesis and most prominently at the osmoregulatory contractile vacuole (CV). Consistently, IBARa-null mutants displayed defects in CV formation and discharge, growth, phagocytosis and mitotic cell division, whereas filopodia formation was not compromised. Of note, IBARa-null mutants were also strongly impaired in cell spreading. Taken together, these data suggest that IBARa constitutes an important regulator of numerous cellular processes intimately linked with the dynamic rearrangement of cellular membranes.

ADiaphanous-related formin links Ras signaling directly to actin assembly in macropinocytosis and phagocytosis

“…3D). Impaired growth in shaken suspension or on bacterial lawns as seen with the forG − cells can occur due to poor uptake of nutrients as previously observed in PI3K multinull mutants and in KOs lacking their upstream activator Ras (15,34), but it can also be caused by defects in cell division as shown for myosin II-or IBARa-null mutants (35,36). However, due to the clear accumulation of ForG in macropinosomes and phagosomes, as well as the normal size of forG − cells in suspension, we reasoned that reduced nutrient uptake in the mutant cells was the most likely cause, and we therefore investigated fluid-phase and particle uptake in more detail.…”

The I-BAR protein Ivy1 is an effector of the Rab7 GTPase Ypt7 involved in vacuole membrane homeostasis

“…Recently, a new I-BAR protein that affects phagocytosis and cytokinesis was characterized in Dictyostelium discoideum (Linkner et al, 2014). Like Ivy1, IBARa localizes to the vacuole in a PI3P-dependent manner and does not seem to affect the formation of filopodia.…”

Vesicle Fusion Triggered by Optically Heated Gold Nanoparticles

“…30,31 Also, I-BAR has been shown by cryo-electron microscopy to induce tubules of specific radii that were found to be 55−60 nm in diameter. 30 Until now, however, it has not been possible to measure the kinetics of tube formation in real time and, more importantly, I-BAR was always added to the outside of the spherical membranes resulting in inward directed tubes although its natural presence in cells is inside filopodia that protrude outward.…”