Biology subjects

Lis, A.

Publications and source records attributed to Lis, A..

3 recordsLinked to original sources

bioRxiv2023

Identification of Toxoplasma Calcium Dependent Protein Kinase 3 as a Stress-Activated Elongation Factor 2 Kinase

Toxoplasma gondii is an obligate intracellular parasite whose tachyzoite form causes disease via a lytic growth cycle. Its metabolic and cellular pathways are primarily designed to ensure parasite survival within a host cell. But during its lytic cycle tachyzoites are exposed to the extracellular milieu and prolonged exposure requires activation of stress response pathways that include reprogramming the parasite proteome. Regulation of protein synthesis is therefore important for extracellular survival. We previously reported that in extracellularly stressed parasites that the elongation phase of protein synthesis is negatively regulated by the Toxoplasma oxygen sensing protein, PhyB. PhyB acts by promoting the activity of elongation factor eEF2, which is a GTPase that catalyzes the transfer of the peptidyl-tRNA from the A site to the P site of the ribosome. In the absence of PhyB, eEF2 is hyper-phosphorylated, which inhibits eEF2 from interacting with the ribosome. eEF2 kinases are atypical calcium-dependent kinases and BLAST analyses revealed the parasite kinase, CDPK3, as the most highly homologous to the Saccharomyces cerevisiae eEF2 kinase, RCK2. In parasites exposed to extracellular stress, loss of CDPK3 leads to decreased eEF2 phosphorylation and enhanced rates of elongation. Furthermore, co-immunoprecipitation studies revealed that CDPK3 and eEF2 interact in stressed parasites. Since CDPK3 and eEF2 normally localize to the plasma membrane and cytosol, respectively, we investigated how the two can interact. We report that under stress conditions that CDPK3 is not N-myristoylated likely leading to its cytoplasmic localization. In summary, we have identified a novel function for CDPK3 as the first protozoan extracellular-stress induced eEF2 kinase. IMPORTANCEHere, we identify the first protozoan kinase that phosphorylate elongation factor 2 and demonstrate that it is part of an integrated stress response.

microbiology↗

bioRxiv2020

Alternative splicing switches STIM1 targeting to specialized membrane contact sites and modifies SOCE

Alternative splicing is a potent modifier of protein function. Stromal interaction molecule 1 (Stim1) is the essential activator molecule of store-operated Ca2+ entry (SOCE) and a sorting regulator of certain ER proteins such as Stimulator of interferon genes (STING). Here, we characterize a conserved new variant, Stim1A, where splice-insertion translates into an additional C-terminal domain. We find prominent expression of exonA mRNA in testes, astrocytes, kidney and heart and confirm Stim1A protein in Western blot of testes. In situ, endogenous Stim1 with domain A, but not Stim1 without domain A localizes to unique adhesion junctions and to specialized membrane retrieval sites (tubulobulbar complexes) in testes. Functionally, using Ca2+ imaging and patch-clamp analysis, Stim1A shows a dominant-negative effect on SOCE and ICRAC, despite normal clustering and interaction with Orai1 investigated by combined TIRF and FRET analyses and as confirmed by an increased SOCE upon knock-down of endogenous Stim1A in astrocytes. Mutational analyses in conjunction with imaging and patch-clamp analyses of residues either in domain A or within the N-terminal region of Orai1 demonstrate a specific defect in stabilized channel gating. Our findings demonstrate that cell-type specific splicing of STIM1 adds both an intracellular targeting switch and adapts SOCE to meet the Ca2+ requirements of specific subcellular contact sites.

molecular biology↗

bioRxiv2019

Toxoplasma F-Box Protein 1 is Required for Daughter Cell Scaffold Function During Parasite Replication

By binding to the adaptor protein SKP1 and serving as substrate receptors for the Skp1, Cullin, F-box E3 ubiquitin ligase complex, F-box proteins regulate critical cellular processes including cell cycle progression and membrane trafficking. While F-box proteins are conserved throughout eukaryotes and are well studied in yeast, plants, and animals, studies in parasitic protozoa are lagging. We have identified eighteen putative F-box proteins in the Toxoplasma genome of which four have predicted homologs in Plasmodium. Two of the conserved F-box proteins were demonstrated to be important for Toxoplasma fitness and here we focus on an F-box protein, named TgFBXO1, because it is the most highly expressed by replicative tachyzoites and was also identified in an interactome screen as a Toxoplasma SKP1 binding protein. TgFBXO1 interacts with Toxoplasma SKP1 confirming it as a bona fide F-box protein. In interphase parasites, TgFBXO1 is a component of the Inner Membrane Complex (IMC), which is an organelle that underlies the plasma membrane. Early during replication, TgFBXO1 localizes to the developing daughter cell scaffold, which is the site where the daughter cell IMC and microtubules form and extend from. TgFBXO1 localization to the daughter cell scaffold required centrosome duplication but occurred before segregation of the centrocone, which connects the spindle pole to the centrosomes. Daughter cell scaffold localization required TgFBXO1 N-myristoylation and was dependent on the small molecular weight GTPase, TgRab11b. Finally, we demonstrate that TgFBXO1 is required for parasite growth due to its function as a daughter cell scaffold effector. TgFBXO1 is the first F-box protein to be studied in apicomplexan parasites and represents the first protein demonstrated to be important for daughter cell scaffold function.\n\nAUTHOR SUMMARYToxoplasma gondii is a protozoan parasite that can cause devastating and life-threatening disease in immunocompromised patients and in fetuses. Its replication is important to study because parasite growth is responsible for the pathology that develops in toxoplasmosis patients. The parasite replicates by a unique process named endodyogeny in which two daughter parasites develop within the mother cell. Early during this process the parasite creates a structure called the Daughter Cell Scaffold whose function is to mark the site from which daughter parasites will emerge. Here, we report the identification of one of the first proteins recruited to the Daughter Cell Scaffold and its importance in executing its function.

microbiology↗