TY - JOUR A1 - Bar-Yosef, Hagit A1 - Gildor, Tsvia A1 - Ramírez-Zavala, Bernardo A1 - Schmauch, Christian A1 - Weissman, Ziva A1 - Pinsky, Mariel A1 - Naddaf, Rawi A1 - Morschhäuser, Joachim A1 - Arkowitz, Robert A. A1 - Kornitzer, Daniel T1 - A global analysis of kinase function in Candida albicans hyphal morphogenesis reveals a role for the endocytosis regulator Akl1 JF - Frontiers in Cellular and Infection Microbiology N2 - The human pathogenic fungus Candida albicans can switch between yeast and hyphal morphologies as a function of environmental conditions and cellular physiology. The yeast-to-hyphae morphogenetic switch is activated by well-established, kinase-based signal transduction pathways that are induced by extracellular stimuli. In order to identify possible inhibitory pathways of the yeast-to-hyphae transition, we interrogated a collection of C. albicans protein kinases and phosphatases ectopically expressed under the regulation of the TETon promoter. Proportionately more phosphatases than kinases were identified that inhibited hyphal morphogenesis, consistent with the known role of protein phosphorylation in hyphal induction. Among the kinases, we identified AKL1 as a gene that significantly suppressed hyphal morphogenesis in serum. Akl1 specifically affected hyphal elongation rather than initiation: overexpression of AKL1 repressed hyphal growth, and deletion of AKL1 resulted in acceleration of the rate of hyphal elongation. Akl1 suppressed fluid-phase endocytosis, probably via Pan1, a putative clathrin-mediated endocytosis scaffolding protein. In the absence of Akl1, the Pan1 patches were delocalized from the sub-apical region, and fluid-phase endocytosis was intensified. These results underscore the requirement of an active endocytic pathway for hyphal morphogenesis. Furthermore, these results suggest that under standard conditions, endocytosis is rate-limiting for hyphal elongation. KW - hyphae KW - endocytosis KW - Pan1 KW - functional genomics Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-197204 SN - 2235-2988 VL - 8 ER - TY - JOUR A1 - Paponov, Ivan A. A1 - Dindas , Julian A1 - Król , Elżbieta A1 - Friz, Tatyana A1 - Budnyk, Vadym A1 - Teale, William A1 - Paponov, Martina A1 - Hedrich , Rainer A1 - Palme, Klaus T1 - Auxin-Induced plasma membrane depolarization is regulated by Auxin transport and not by AUXIN BINDING PROTEIN1 JF - Frontiers in Plant Science N2 - Auxin is a molecule, which controls many aspects of plant development through both transcriptional and non-transcriptional signaling responses. AUXIN BINDING PROTEIN1 (ABP1) is a putative receptor for rapid non-transcriptional auxin-induced changes in plasma membrane depolarization and endocytosis rates. However, the mechanism of ABP1-mediated signaling is poorly understood. Here we show that membrane depolarization and endocytosis inhibition are ABP1-independent responses and that auxin-induced plasma membrane depolarization is instead dependent on the auxin influx carrier AUX1. AUX1 was itself not involved in the regulation of endocytosis. Auxin-dependent depolarization of the plasma membrane was also modulated by the auxin efflux carrier PIN2. These data establish a new connection between auxin transport and non-transcriptional auxin signaling. KW - auxin KW - ABP1 KW - plasma membrane depolarization KW - AUX1 KW - endocytosis Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-195914 SN - 1664-462X VL - 9 ER - TY - JOUR A1 - Sajko, Sara A1 - Grishkovskaya, Irina A1 - Kostan, Julius A1 - Graewert, Melissa A1 - Setiawan, Kim A1 - Trübestein, Linda A1 - Niedermüller, Korbinian A1 - Gehin, Charlotte A1 - Sponga, Antonio A1 - Puchinger, Martin A1 - Gavin, Anne-Claude A1 - Leonard, Thomas A. A1 - Svergun, Dimitri I. A1 - Smith, Terry K. A1 - Morriswood, Brooke A1 - Djinovic-Carugo, Kristina T1 - Structures of three MORN repeat proteins and a re-evaluation of the proposed lipid-binding properties of MORN repeats JF - PLoS One N2 - MORN (Membrane Occupation and Recognition Nexus) repeat proteins have a wide taxonomic distribution, being found in both prokaryotes and eukaryotes. Despite this ubiquity, they remain poorly characterised at both a structural and a functional level compared to other common repeats. In functional terms, they are often assumed to be lipid-binding modules that mediate membrane targeting. We addressed this putative activity by focusing on a protein composed solely of MORN repeats-Trypanosoma brucei MORN1. Surprisingly, no evidence for binding to membranes or lipid vesicles by TbMORN1 could be obtained either in vivo or in vitro. Conversely, TbMORN1 did interact with individual phospholipids. High- and low-resolution structures of the MORN1 protein from Trypanosoma brucei and homologous proteins from the parasites Toxoplasma gondii and Plasmodium falciparum were obtained using a combination of macromolecular crystallography, small-angle X-ray scattering, and electron microscopy. This enabled a first structure-based definition of the MORN repeat itself. Furthermore, all three structures dimerised via their C-termini in an antiparallel configuration. The dimers could form extended or V-shaped quaternary structures depending on the presence of specific interface residues. This work provides a new perspective on MORN repeats, showing that they are protein-protein interaction modules capable of mediating both dimerisation and oligomerisation. KW - recognition nexus domain KW - trypanosoma brucei KW - blood stream KW - phosphatidylserine transport KW - biological macromolecules KW - membrane occupation KW - solution scattering KW - molecular cloning KW - flagellar pocket KW - endocytosis Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-231261 VL - 15 IS - 23 ER - TY - JOUR A1 - Broster Reix, Christine E. A1 - Florimond, Célia A1 - Cayrel, Anne A1 - Mailhé, Amélie A1 - Agnero-Rigot, Corentin A1 - Landrein, Nicolas A1 - Dacheux, Denis A1 - Havlicek, Katharina A1 - Bonhivers, Mélanie A1 - Morriswood, Brooke A1 - Robinson, Derrick R. T1 - Bhalin, an essential cytoskeleton-associated protein of Trypanosoma brucei linking TbBILBO1 of the flagellar pocket collar with the hook complex JF - Microorganisms N2 - Background: In most trypanosomes, endo and exocytosis only occur at a unique organelle called the flagellar pocket (FP) and the flagellum exits the cell via the FP. Investigations of essential cytoskeleton-associated structures located at this site have revealed a number of essential proteins. The protein TbBILBO1 is located at the neck of the FP in a structure called the flagellar pocket collar (FPC) and is essential for biogenesis of the FPC and parasite survival. TbMORN1 is a protein that is present on a closely linked structure called the hook complex (HC) and is located anterior to and overlapping the collar. TbMORN1 is essential in the bloodstream form of T. brucei. We now describe the location and function of BHALIN, an essential, new FPC-HC protein. Methodology/Principal Findings: Here, we show that a newly characterised protein, BHALIN (BILBO1 Hook Associated LINker protein), is localised to both the FPC and HC and has a TbBILBO1 binding domain, which was confirmed in vitro. Knockdown of BHALIN by RNAi in the bloodstream form parasites led to cell death, indicating an essential role in cell viability. Conclusions/Significance: Our results demonstrate the essential role of a newly characterised hook complex protein, BHALIN, that influences flagellar pocket organisation and function in bloodstream form T. brucei parasites. KW - trypanosoma KW - flagellar pocket KW - hook complex KW - endocytosis KW - cytoskeleton KW - protozoan KW - flagellar pocket collar Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-250301 SN - 2076-2607 VL - 9 IS - 11 ER - TY - JOUR A1 - Link, Fabian A1 - Borges, Alyssa R. A1 - Jones, Nicola G. A1 - Engstler, Markus T1 - To the Surface and Back: Exo- and Endocytic Pathways in Trypanosoma brucei JF - Frontiers in Cell and Developmental Biology N2 - Trypanosoma brucei is one of only a few unicellular pathogens that thrives extracellularly in the vertebrate host. Consequently, the cell surface plays a critical role in both immune recognition and immune evasion. The variant surface glycoprotein (VSG) coats the entire surface of the parasite and acts as a flexible shield to protect invariant proteins against immune recognition. Antigenic variation of the VSG coat is the major virulence mechanism of trypanosomes. In addition, incessant motility of the parasite contributes to its immune evasion, as the resulting fluid flow on the cell surface drags immunocomplexes toward the flagellar pocket, where they are internalized. The flagellar pocket is the sole site of endo- and exocytosis in this organism. After internalization, VSG is rapidly recycled back to the surface, whereas host antibodies are thought to be transported to the lysosome for degradation. For this essential step to work, effective machineries for both sorting and recycling of VSGs must have evolved in trypanosomes. Our understanding of the mechanisms behind VSG recycling and VSG secretion, is by far not complete. This review provides an overview of the trypanosome secretory and endosomal pathways. Longstanding questions are pinpointed that, with the advent of novel technologies, might be answered in the near future. KW - cell surface KW - African trypanosomes KW - endocytosis KW - exocytosis KW - membrane recycling KW - Rab KW - clathrin Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-244682 SN - 2296-634X VL - 9 ER -