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Biochemical Society Transactions Dec 2023Mitochondria are vital to the functions of eukaryotic cells. Most mitochondrial proteins are transported into the organelle following their synthesis by cytoplasmic... (Review)
Review
Mitochondria are vital to the functions of eukaryotic cells. Most mitochondrial proteins are transported into the organelle following their synthesis by cytoplasmic ribosomes. However, precise protein targeting is complex because the two diverse lipid membranes encase mitochondria. Efficient protein translocation across membranes and accurate sorting to specific sub-compartments require the cooperation of multiple factors. Any failure in mitochondrial protein import can disrupt organelle fitness. Proteins intended for mitochondria make up a significant portion of all proteins produced in the cytosol. Therefore, import defects causing their mislocalization can significantly stress cellular protein homeostasis. Recognition of this phenomenon has increased interest in molecular mechanisms that respond to import-related stress and restore proteostasis, which is the focus of this review. Significantly, disruptions in protein homeostasis link strongly to the pathology of several degenerative disorders highly relevant in ageing societies. A comprehensive understanding of protein import quality control will allow harnessing this machinery in therapeutic approaches.
Topics: Mitochondria; Protein Transport; Mitochondrial Proteins; Biological Transport; Cytosol
PubMed: 37987513
DOI: 10.1042/BST20230377 -
Current Opinion in Structural Biology Apr 2020Helicases are ATP-dependent motor proteins that translocate along single-stranded or double-stranded nucleic acids to alter base-pairing structures or molecular... (Review)
Review
Helicases are ATP-dependent motor proteins that translocate along single-stranded or double-stranded nucleic acids to alter base-pairing structures or molecular interactions. Helicases can be divided to monomeric and hexameric types, each with distinct ternary structures, nucleic acid-binding modes, and translocation mechanisms. It is well established that monomeric helicases translocate by the inchworm mechanism. Recent structures of different superfamilies of hexameric helicases reveal that they use a hand-over hand mechanism for translocation. Structures of bacteriophage T7 replisome illustrate how helicase and polymerase cooperatively catalyze DNA unwinding. In this review, we survey structures of monomeric and hexameric helicases and compare different mechanisms for translocation.
Topics: DNA Helicases; Humans; Hydrolysis; Models, Molecular; Protein Binding; Protein Conformation; Protein Multimerization; Protein Transport; Structure-Activity Relationship
PubMed: 31783299
DOI: 10.1016/j.sbi.2019.10.003 -
Cellular Microbiology Jul 2020The ability of eukaryotic parasites from the phylum Apicomplexa to cause devastating diseases is predicated upon their ability to maintain faithful and precise protein... (Review)
Review
The ability of eukaryotic parasites from the phylum Apicomplexa to cause devastating diseases is predicated upon their ability to maintain faithful and precise protein trafficking mechanisms. Their parasitic life cycle depends on the trafficking of effector proteins to the infected host cell, transport of proteins to several critical organelles required for survival, as well as transport of parasite and host proteins to the digestive organelles to generate the building blocks for parasite growth. Several recent studies have shed light on the molecular mechanisms parasites utilise to transform the infected host cells, transport proteins to essential metabolic organelles and for biogenesis of organelles required for continuation of their life cycle. Here, we review key pathways of protein transport originating and branching from the endoplasmic reticulum, focusing on the essential roles of chaperones in these processes. Further, we highlight key gaps in our knowledge that prevents us from building a holistic view of protein trafficking in these deadly human pathogens.
Topics: Animals; Apicomplexa; Apicoplasts; Endoplasmic Reticulum; Humans; Malaria; Parasites; Protein Transport; Protozoan Proteins; Vacuoles
PubMed: 32388921
DOI: 10.1111/cmi.13215 -
Cytoskeleton (Hoboken, N.J.) Aug 2020Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins are a large protein complex that is involved in the membrane fusion in vesicle... (Review)
Review
Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins are a large protein complex that is involved in the membrane fusion in vesicle trafficking, cell growth, cytokinesis, membrane repair, and synaptic transmission. As one of the SNARE proteins, SEC22B functions in membrane fusion of vesicle trafficking between the endoplasmic reticulum and the Golgi apparatus, antigen cross-presentation, secretory autophagy, and other biological processes. However, apart from not being SNARE proteins, there is little knowledge known about its two homologs (SEC22A and SEC22C). SEC22B alterations have been reported in many human diseases, especially, many mutations of SEC22B in human cancers have been detected. In this review, we will introduce the specific functions of SEC22B, and summarize the researches about SEC22B in human cancers and other diseases. These findings have laid the foundation for further studies to clarify the exact mechanism of SEC22B in the pathological process and to seek new therapeutic targets and better treatment strategies.
Topics: Disease; Humans; Protein Transport; R-SNARE Proteins
PubMed: 32748571
DOI: 10.1002/cm.21628 -
Cells Aug 2019Membraneless organelles (MLOs) are defined as cellular structures that are not sealed by a lipidic membrane and are shown to form by phase separation. They exist in both... (Review)
Review
Membraneless organelles (MLOs) are defined as cellular structures that are not sealed by a lipidic membrane and are shown to form by phase separation. They exist in both the nucleus and the cytoplasm that is also heavily populated by numerous membrane-bound organelles. Even though the name membraneless suggests that MLOs are free of membrane, both membrane and factors regulating membrane trafficking steps are emerging as important components of MLO formation and function. As a result, we name them biocondensates. In this review, we examine the relationships between biocondensates and membrane. First, inhibition of membrane trafficking in the early secretory pathway leads to the formation of biocondensates (P-bodies and Sec bodies). In the same vein, stress granules have a complex relationship with the cyto-nuclear transport machinery. Second, membrane contributes to the regulated formation of phase separation in the cells and we will present examples including clustering at the plasma membrane and at the synapse. Finally, the whole cell appears to transit from an interphase phase-separated state to a mitotic diffuse state in a DYRK3 dependent manner. This firmly establishes a crosstalk between the two types of cell organization that will need to be further explored.
Topics: Active Transport, Cell Nucleus; Animals; Caenorhabditis elegans; Cell Membrane; Cell Nucleus; Cells; Cytoplasm; Drosophila; Humans; Organelles; Plants; Protein Translocation Systems; Proteins; Yeasts
PubMed: 31470564
DOI: 10.3390/cells8091000 -
Cytokine May 2020Effector CD4 T cells can be classified by the cytokines they secrete, with T helper 1 (Th1) cells generating interferon (IFN)γ and Th17 cells secreting interleukin...
Effector CD4 T cells can be classified by the cytokines they secrete, with T helper 1 (Th1) cells generating interferon (IFN)γ and Th17 cells secreting interleukin (IL)-17. Both Th1 and Th17 cells are strongly implicated in the initiation and chronicity of autoimmune diseases such as multiple sclerosis. The endoplasmic reticulum (ER) has been implicated as a potentially crucial site in regulating CD4 T cell function. Secretory and transmembrane proteins are shuttled into the ER via the Sec61 translocon, where they undergo appropriate folding; misfolded proteins are retro-translocated from the ER in a p97-dependent manner. Here, we provide evidence that both processes are crucial to the secretion of inflammatory cytokines from effector CD4 T cells. The pan-ER inhibitor eeeyarestatin-1 (ESI), which interferes with both Sec61 translocation and p97 retro-translocation, inhibited secretion of interferon (IFN)γ, interleukin (IL)-2 and tumor necrosis factor (TNF)α from Th1 cells in a dose-dependent manner. Selective inhibition of Sec61 by Apratoxin A (ApraA) revealed that ER translocation is crucial for Th1 cytokine secretion, while inhibition of p97 by NMS-873 also inhibited Th1 function, albeit to a lesser degree. By contrast, none of ESI, ApraA or NMS-873 could significantly reduce IL-17 secretion from Th17 cells. ApraA, but not NMS-873, reduced phosphorylation of Stat1 in Th1 cells, indicating the involvement of ER translocation in Th1 differentiation pathways. ApraA had modest effects on activation of the Th17 transcription factor Stat3, while NMS-873 had no effect. Interestingly, NMS-873 was able to reduce disease severity in CD4 T cell-driven experimental autoimmune encephalomyelitis (EAE). Together, our data indicate that CD4 T cell function, and Th1 cell function in particular, is dependent on protein translocation and dislocation across the ER.
Topics: Animals; CD4-Positive T-Lymphocytes; Cell Differentiation; Central Nervous System; Cytokines; Encephalomyelitis, Autoimmune, Experimental; Endoplasmic Reticulum; Inflammation; Interferon-gamma; Interleukin-17; Mice; Mice, Inbred C57BL; Multiple Sclerosis; Protein Transport; Th1 Cells; Th17 Cells
PubMed: 32146280
DOI: 10.1016/j.cyto.2019.154944 -
Autophagy Nov 2020Several studies have provided insight into the unique intracellular localization, dynamic trafficking and diverse repertoire of binding partners of Atg9/ATG9, but...
Several studies have provided insight into the unique intracellular localization, dynamic trafficking and diverse repertoire of binding partners of Atg9/ATG9, but structural details of the protein have remained elusive. Guardia and colleagues now report the structure of human ATG9A to a resolution of 2.9 Å, revealing, among other features, an elaborate system of tunnels permeating the ATG9A protein complex.
Topics: Autophagosomes; Autophagy; Autophagy-Related Proteins; Humans; Membrane Proteins; Protein Transport; Vesicular Transport Proteins
PubMed: 32840139
DOI: 10.1080/15548627.2020.1810901 -
Methods in Molecular Biology (Clifton,... 2021Alpha synuclein (α-Syn), a presynaptic protein with unknown function, is accumulated in Lewy bodies/neurites that are one of the hallmark pathologies of Parkinson's...
Alpha synuclein (α-Syn), a presynaptic protein with unknown function, is accumulated in Lewy bodies/neurites that are one of the hallmark pathologies of Parkinson's disease (PD). Missense or multiplication mutations in SNCA, which codes α-Syn, result in a genetic form of PD, further indicating the involvement of α-Syn in PD pathogenesis. Recent pathological and experimental studies suggest that α-Syn possesses a secretory feature, as it is detected in the culture media, in the cerebrospinal fluid, and even in the blood. Secreted α-Syn can spread throughout the body and invade the CNS, disseminating the α-Syn associated pathology. Exosomes are small extracellular vesicles that carry many proteins, lipids, or miRNA. We and others have discovered α-Syn in exosomes and revealed that exosomes may regulate intracellular α-Syn levels by transporting outside the cells. In this chapter, we describe a protocol to measure α-Syn levels in exosomes.
Topics: Exosomes; Humans; Mutation; Neurons; Parkinson Disease; Protein Transport; alpha-Synuclein
PubMed: 34043190
DOI: 10.1007/978-1-0716-1495-2_4 -
International Journal of Molecular... Aug 2020The p38 mitogen-activated protein kinase (p38MAPK, termed here p38) cascade is a central signaling pathway that transmits stress and other signals to various... (Review)
Review
The p38 mitogen-activated protein kinase (p38MAPK, termed here p38) cascade is a central signaling pathway that transmits stress and other signals to various intracellular targets in the cytoplasm and nucleus. More than 150 substrates of p38α/β have been identified, and this number is likely to increase. The phosphorylation of these substrates initiates or regulates a large number of cellular processes including transcription, translation, RNA processing and cell cycle progression, as well as degradation and the nuclear translocation of various proteins. Being such a central signaling cascade, its dysregulation is associated with many pathologies, particularly inflammation and cancer. One of the hallmarks of p38α/β signaling is its stimulated nuclear translocation, which occurs shortly after extracellular stimulation. Although p38α/β do not contain nuclear localization or nuclear export signals, they rapidly and robustly translocate to the nucleus, and they are exported back to the cytoplasm within minutes to hours. Here, we describe the physiological and pathological roles of p38α/β phosphorylation, concentrating mainly on the ill-reviewed regulation of p38α/β substrate degradation and nuclear translocation. In addition, we provide information on the p38α/β 's substrates, concentrating mainly on the nuclear targets and their role in p38α/b functions. Finally, we also provide information on the mechanisms of nuclear p38α/b translocation and its use as a therapeutic target for p38α/β-dependent diseases.
Topics: Active Transport, Cell Nucleus; Animals; Cell Nucleus; Humans; Inflammation; Neoplasms; Phosphorylation; Protein Processing, Post-Translational; Protein Transport; Proteolysis; Signal Transduction; p38 Mitogen-Activated Protein Kinases
PubMed: 32847129
DOI: 10.3390/ijms21176102 -
Cell Reports Jan 2023Translocon clogging at the endoplasmic reticulum (ER) as a result of translation stalling triggers ribosome UFMylation, activating translocation-associated quality...
Translocon clogging at the endoplasmic reticulum (ER) as a result of translation stalling triggers ribosome UFMylation, activating translocation-associated quality control (TAQC) to degrade clogged substrates. How cells sense ribosome UFMylation to initiate TAQC is unclear. We conduct a genome-wide CRISPR-Cas9 screen to identify an uncharacterized membrane protein named SAYSD1 that facilitates TAQC. SAYSD1 associates with the Sec61 translocon and also recognizes both ribosome and UFM1 directly, engaging a stalled nascent chain to ensure its transport via the TRAPP complex to lysosomes for degradation. Like UFM1 deficiency, SAYSD1 depletion causes the accumulation of translocation-stalled proteins at the ER and triggers ER stress. Importantly, disrupting UFM1- and SAYSD1-dependent TAQC in Drosophila leads to intracellular accumulation of translocation-stalled collagens, defective collagen deposition, abnormal basement membranes, and reduced stress tolerance. Thus, SAYSD1 acts as a UFM1 sensor that collaborates with ribosome UFMylation at the site of clogged translocon, safeguarding ER homeostasis during animal development.
Topics: Animals; Basement Membrane; Drosophila; Endoplasmic Reticulum; Fenbendazole; Membrane Proteins; Protein Transport; Ribosomes; Drosophila Proteins
PubMed: 36848233
DOI: 10.1016/j.celrep.2023.112028