bims-mecosi 2022-07-17 papers

Issue of 2022–07–17
four papers selected by
Verena Kohler, Stockholm University

Elife. 2022 Jul 15. pii: e74535. [Epub ahead of print]11

Phosphoregulation accommodates Type III secretion and assembly of a tether of ER-Chlamydia inclusion membrane contact sites.

Rachel J Ende, Rebecca L Murray, Samantha K D'Spain, Isabelle Coppens, Isabelle Derré.

Membrane contact sites (MCS) are crucial for nonvesicular trafficking-based interorganelle communication. Endoplasmic reticulum (ER)-organelle tethering occurs in part through the interaction of the ER resident protein VAP with FFAT motif-containing proteins. FFAT motifs are characterized by a seven amino acidic core surrounded by acid tracks. We have previously shown that the human intracellular bacterial pathogen Chlamydia trachomatis establishes MCS between its vacuole (the inclusion) and the ER through expression of a bacterial tether, IncV, displaying molecular mimicry of eukaryotic FFAT motif cores. Here, we show that multiple layers of host cell kinase-mediated phosphorylation events govern the assembly of the IncV-VAP tethering complex and the formation of ER-Inclusion MCS. Via a C-terminal region containing three CK2 phosphorylation motifs, IncV recruits CK2 to the inclusion leading to IncV hyperphosphorylation of the noncanonical FFAT motif core and serine-rich tracts immediately upstream of IncV FFAT motif cores. Phosphorylatable serine tracts, rather than genetically encoded acidic tracts, accommodate Type III-mediated translocation of IncV to the inclusion membrane, while achieving full mimicry of FFAT motifs. Thus, regulatory components and post-translational modifications are integral to MCS biology, and intracellular pathogens such as C. trachomatis have evolved complex molecular mimicry of these eukaryotic features.

Keywords: CK2; Chlamydia trachomatis; FFAT; VAP; cell biology; chlamydia inclusion membrane protein incv; endoplasmic reticulum; infectious disease; membrane contact sites; microbiology

DOI: https://doi.org/10.7554/eLife.74535

Methods Mol Biol. 2022 ;2525 197-205

MERLIN: A BRET-Based Proximity Biosensor for Studying Mitochondria-ER Contact Sites.

Hector Flores-Romero, Ana J García-Sáez.

The contacts between the endoplasmic reticulum (ER) and mitochondria play a fundamental role in a wide variety of cellular processes, like the exchange of calcium and lipids between both organelles, as well as in apoptosis and in autophagy signaling. Despite their importance, due to their dynamic and heterogeneous nature, we still lack understanding of the molecular composition, structure, and regulation of these structures. In this chapter, we introduce a new bioluminescence resonance energy transfer (BRET)-based biosensor for the quantitative analysis of mitochondria-ER interorganellar distances without perturbing their natural environment, which we call MERLIN (mitochondria ER length indicator nanosensor). Here, we describe the rationale behind the MERLIN biosensor, detail the experimental setup and methodology, and provide tips for troubleshooting.

Keywords: Bioluminescence resonance energy transfer (BRET); Biosensor; Endoplasmic reticulum (ER); Mitochondria; Mitochondria ER contact sites (MERCs); Mitochondria ER length indicator nanosensor (MERLIN)

DOI: https://doi.org/10.1007/978-1-0716-2473-9_14

Life Sci Alliance. 2022 Nov;pii: e202201531. [Epub ahead of print]5(11):

Decreasing pdzd8-mediated mito-ER contacts improves organismal fitness and mitigates Aβ42 toxicity.

Victoria L Hewitt, Leonor Miller-Fleming, Madeleine J Twyning, Simonetta Andreazza, Francesca Mattedi, Julien Prudent, Franck Polleux, Alessio Vagnoni, Alexander J Whitworth.

Mitochondria-ER contact sites (MERCs) orchestrate many important cellular functions including regulating mitochondrial quality control through mitophagy and mediating mitochondrial calcium uptake. Here, we identify and functionally characterize the Drosophila ortholog of the recently identified mammalian MERC protein, Pdzd8. We find that reducing pdzd8-mediated MERCs in neurons slows age-associated decline in locomotor activity and increases lifespan in Drosophila. The protective effects of pdzd8 knockdown in neurons correlate with an increase in mitophagy, suggesting that increased mitochondrial turnover may support healthy aging of neurons. In contrast, increasing MERCs by expressing a constitutive, synthetic ER-mitochondria tether disrupts mitochondrial transport and synapse formation, accelerates age-related decline in locomotion, and reduces lifespan. Although depletion of pdzd8 prolongs the survival of flies fed with mitochondrial toxins, it is also sufficient to rescue locomotor defects of a fly model of Alzheimer's disease expressing Amyloid β42 (Aβ42). Together, our results provide the first in vivo evidence that MERCs mediated by the tethering protein pdzd8 play a critical role in the regulation of mitochondrial quality control and neuronal homeostasis.

DOI: https://doi.org/10.26508/lsa.202201531

Curr Biol. 2022 Jul 11. pii: S0960-9822(22)00785-0. [Epub ahead of print]32(13): R748-R750

Vesicle transport: Exocyst follows PIP2 to tether membranes.

Lars Langemeyer, Christian Ungermann.

A new study uses reconstituted, functional octameric exocyst complex to provide new insights into the assembly of this tethering complex and reveal how the activity of the lipid kinase PIP5K1C stimulated by Arf6 on exocytic vesicles allows for exocyst-mediated tethering at the plasma membrane.

DOI: https://doi.org/10.1016/j.cub.2022.05.026