Cytosol

Summary

The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells (intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into many compartments. In the eukaryotic cell, the cytosol is surrounded by the cell membrane and is part of the cytoplasm, which also comprises the mitochondria, plastids, and other organelles (but not their internal fluids and structures); the cell nucleus is separate. The cytosol is thus a liquid matrix around the organelles. In prokaryotes, most of the chemical reactions of metabolism take place in the cytosol, while a few take place in membranes or in the periplasmic space. In eukaryotes, while many metabolic pathways still occur in the cytosol, others take place within organelles. The cytosol is a complex mixture of substances dissolved in water. Although water forms the large majority of the cytosol, its structure and properties wi

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Host cell entry of vaccinia virus, the prototypic poxvirus, involves a membrane fusion event delivering the viral core and two proteinaceous lateral bodies (LBs) into the cytosol. Uncoating of viral cores is poorly characterized, and the composition and function of LBs remains enigmatic. We found that cytosolic cores rapidly dissociated from LBs and expanded in volume, which coincided with reduction of disulfide-bonded core proteins. We identified the abundant phosphoprotein F17, the dual-specificity phosphatase VH1, and the oxidoreductase G4 as bona fide LB components. After reaching the cytosol, F17 was degraded in a proteasome-dependent manner. Proteasome activity, and presumably LB disassembly, was required for the immediate immunomodulatory activity of VH1: dephosphorylation of STAT1 to prevent interferon-gamma-mediated antiviral responses. These results reveal a mechanism used by poxviruses to deliver viral enzymes to the host cell cytosol and are likely to facilitate the identification of additional LB-resident viral effectors.

Elsevier BV2013

3D correlative electron microscopy reveals continuity of Brucella-containing vacuoles with the endoplasmic reticulum

Shyan Huey Low, Henning Paul-Julius Stahlberg

Entry of the facultative intracellular pathogen Brucella into host cells results in the formation of endosomal Brucella-containing vacuoles (eBCVs) that initially traffic along the endocytic pathway. eBCV acidification triggers the expression of a type IV secretion system that translocates bacterial effector proteins into host cells. This interferes with lysosomal fusion of eBCVs and supports their maturation to replicative Brucella-containing vacuoles (rBCVs). Bacteria replicate in rBCVs to large numbers, eventually occupying most of the cytoplasmic volume. As rBCV membranes tightly wrap each individual bacterium, they are constantly being expanded and remodeled during exponential bacterial growth. rBCVs are known to carry endoplasmic reticulum (ER) markers; however, the relationship of the vacuole to the genuine ER has remained elusive. Here, we have reconstructed the 3-dimensional ultrastructure of rBCVs and associated ER by correlative structured illumination microscopy (SIM) and focused ion beam/scanning electron microscopic tomography (FIB/SEM). Studying B. abortus-infected HeLa cells and trophoblasts derived from B. melitensis-infected mice, we demonstrate that rBCVs are complex and interconnected compartments that are continuous with neighboring ER cisternae, thus supporting a model that rBCVs are extensions of genuine ER.

The Company of Biologists2018

L. monocytogenes is a Gram-positive intracellular pathogen that can cause serious disease, like septicemia and meningitis. It is detected in the cytosol by the innate immune system by sensing pathogen ligands. c-di-AMP has recently been shown to be one of them, inducing an interferon response. L. monocytogenes produces this molecule with the DacA protein and secretes it in the host cell cytosol upon infection. A dacA mutant shows a growth defect indicating an important role for c-di-AMP. To get insights into the role of c-di-AMP this study proposes a forward genetic screen on a dacA mutant to find transposon insertions rescuing growth. The screening of 10 thousands mutants led us to find two insertions. A transposon insertion in a gene involved in DNA metabolism partially rescues growth in broth and intracellular culture. A second transposon insertion in a gene involved in energy metabolism was found to partially rescue intracellular growth only.

2011