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Advanced Drug Delivery Reviews May 2022The secreted mucus layer that lines and protects epithelial cells is conserved across diverse species. While the exact composition of this protective layer varies... (Review)
Review
The secreted mucus layer that lines and protects epithelial cells is conserved across diverse species. While the exact composition of this protective layer varies between organisms, certain elements are conserved, including proteins that are heavily decorated with N-acetylgalactosamine-based sugars linked to serines or threonines (O-linked glycosylation). These heavily O-glycosylated proteins, known as mucins, exist in many forms and are able to form hydrated gel-like structures that coat epithelial surfaces. In vivo studies in diverse organisms have highlighted the importance of both the mucin proteins as well as their constituent O-glycans in the protection and health of internal epithelia. Here, we summarize in vivo approaches that have shed light on the synthesis and function of these essential components of mucus.
Topics: Epithelial Cells; Glycosylation; Humans; Mucins; Mucus; Polysaccharides
PubMed: 35278522
DOI: 10.1016/j.addr.2022.114182 -
Current Opinion in Structural Biology Oct 2014The mucosal layer covering our gut epithelium represents the first line of host defenses against the luminal content, while enabling contacts between the resident... (Review)
Review
The mucosal layer covering our gut epithelium represents the first line of host defenses against the luminal content, while enabling contacts between the resident microbiota and the host. Mucus is mainly composed of mucins, large glycoproteins containing a protein core and a high number of O-linked oligosaccharides. Mucin glycans act as binding sites or carbon sources for the intestinal microbes, thereby functioning as a host-specific determinant affecting the microbiota composition and human health. Reflecting the structural diversity of mucin glycans and their prime location, commensal and pathogenic microbes have evolved a range of adhesins allowing their interaction with the host. However, despite the recognised importance of mucin glycans in modulating intestinal homeostasis, information on carbohydrate-binding proteins from gut bacteria is disparate. This review is focussed on recent structural insights into host-microbe interactions mediated by mucins.
Topics: Animals; Bacteria; Binding Sites; Carbohydrate Metabolism; Carbohydrates; Humans; Intestinal Mucosa; Intestines; Models, Molecular; Molecular Conformation; Mucins; Mucous Membrane; Mucus; Protein Binding; Substrate Specificity
PubMed: 25106027
DOI: 10.1016/j.sbi.2014.07.002 -
Archives of Biochemistry and Biophysics Sep 2023Ferritin is a spherical nanocage protein for iron storage, composed of 24 light- or heavy-polypeptide chain subunits. A single ferritin molecule can carry up to 4500... (Review)
Review
Ferritin is a spherical nanocage protein for iron storage, composed of 24 light- or heavy-polypeptide chain subunits. A single ferritin molecule can carry up to 4500 iron atoms in its core, which plays an important role in suppressing intracellular iron toxicity. Serum ferritin levels are used as a marker for the total amount of iron stored in the body. Most serum ferritin is iron-free (apo-ferritin) and it is unclear how ferritin is released from cells. Ferritin is secreted into serum via extracellular vesicles (EVs) or the secretory autophagy pathway but not via the classical endoplasmic reticulum (ER)-to-Golgi secretion pathway. We recently discovered that the level of tetraspanin CD63, a common EV marker, is post-transcriptionally regulated by the intracellular iron level and both CD63 and ferritin expression is induced by iron loading. Ferritin is incorporated into CD63(+)-EVs through the ferritin-specific autophagy adapter molecule, NCOA4, and then secreted from cells. EV production differs drastically depending on cell type and physiological conditions. Extracellular matrix detached cells express pentaspanin prominin 2 and prominin 2(+)-EVs secrete ferritin independently of NCOA4 trafficking. Ferritin is tightly bound to iron in EVs and functions as an iron-carrier protein in the extracellular environment. Cells can suppress ferroptosis by secreting holo-ferritin, which reduces intracellular iron concentration. However, this exposes the neighboring cells receiving the secreted holo-ferritin to a large excess of iron. This results in cellular toxicity through increased generation of reactive oxygen species (ROS). Here we review the machinery by which ferritin is incorporated into EVs and its role as an intercellular communication molecule.
Topics: AC133 Antigen; Biological Transport; Extracellular Vesicles; Autophagy; Ferritins
PubMed: 37683905
DOI: 10.1016/j.abb.2023.109737 -
Pflugers Archiv : European Journal of... Apr 2024The transport of bicarbonate across the enterocyte cell membrane regulates the intracellular as well as the luminal pH and is an essential part of directional fluid... (Review)
Review
The transport of bicarbonate across the enterocyte cell membrane regulates the intracellular as well as the luminal pH and is an essential part of directional fluid movement in the gut. Since the first description of "active" transport of HCO ions against a concentration gradient in the 1970s, the fundamental role of HCO transport for multiple intestinal functions has been recognized. The ion transport proteins have been identified and molecularly characterized, and knockout mouse models have given insight into their individual role in a variety of functions. This review describes the progress made in the last decade regarding novel techniques and new findings in the molecular regulation of intestinal HCO transport in the different segments of the gut. We discuss human diseases with defects in intestinal HCO secretion and potential treatment strategies to increase luminal alkalinity. In the last part of the review, the cellular and organismal mechanisms for acid/base sensing in the intestinal tract are highlighted.
Topics: Animals; Mice; Humans; Bicarbonates; Ion Transport; Enterocytes; Cell Membrane; Bodily Secretions; Hydrogen-Ion Concentration; Cystic Fibrosis Transmembrane Conductance Regulator
PubMed: 38374228
DOI: 10.1007/s00424-024-02914-3 -
Journal of Bacteriology Mar 2021Large clostridial toxins (LCTs) are secreted virulence factors found in several species, including , , , and LCTs are large toxins that lack a secretion signal...
Large clostridial toxins (LCTs) are secreted virulence factors found in several species, including , , , and LCTs are large toxins that lack a secretion signal sequence, and studies by others have shown that the LCTs of , TcdA and TcdB, require a holin-like protein, TcdE, for secretion. The TcdE gene is located on the pathogenicity locus (PaLoc) of , and holin-encoding genes are also present in the LCT-encoded PaLocs from and However, the holin (TpeE) associated with the LCT TpeL has no homology and a different membrane topology than TcdE. In addition, TpeE has a membrane topology identical to that of the TatA protein, which is the core of the twin-arginine translocation (Tat) secretion system. To determine if TpeE was necessary and sufficient to secrete TpeL, the genes from a type C strain of were expressed in a type A strain of , HN13, and secretion was measured using Western blot methods. We found that TpeE was required for TpeL secretion and that secretion was not due to cell lysis. Mutant forms of TpeE lacking an amphipathic helix and a charged C-terminal domain failed to secrete TpeL, and mutations that deleted conserved LCT domains in TpeL indicated that only the full-length protein could be secreted. In summary, we have identified a novel family of holin-like proteins that can function, in some cases, as a system of protein secretion for proteins that need to fold in the cytoplasm. Little is known about the mechanism by which LCTs are secreted. Since LCTs are major virulence factors in clostridial pathogens, we wanted to define the mechanism by which an LCT in , TpeL, is secreted by a protein (TpeE) lacking homology to previously described secretion-associated holins. We discovered that TpeE is a member of a widely dispersed class of holin proteins, and TpeE is necessary for the secretion of TpeL. TpeE bears a high degree of similarity in membrane topology to TatA proteins, which form the pore through which Tat secretion substrates pass through the cytoplasmic membrane. Thus, the TpeE-TpeL secretion system may be a model for understanding not only holin-dependent secretion but also how TatA proteins function in the secretion process.
Topics: Bacterial Proteins; Bacterial Secretion Systems; Bacterial Toxins; Clostridium perfringens; Gene Expression Regulation, Bacterial; Protein Transport
PubMed: 33526612
DOI: 10.1128/JB.00580-20 -
Biotechnology and Bioengineering Feb 2021Despite their therapeutic potential, many protein drugs remain inaccessible to patients since they are difficult to secrete. Each recombinant protein has unique...
Despite their therapeutic potential, many protein drugs remain inaccessible to patients since they are difficult to secrete. Each recombinant protein has unique physicochemical properties and requires different machinery for proper folding, assembly, and posttranslational modifications (PTMs). Here we aimed to identify the machinery supporting recombinant protein secretion by measuring the protein-protein interaction (PPI) networks of four different recombinant proteins (SERPINA1, SERPINC1, SERPING1, and SeAP) with various PTMs and structural motifs using the proximity-dependent biotin identification (BioID) method. We identified PPIs associated with specific features of the secreted proteins using a Bayesian statistical model and found proteins involved in protein folding, disulfide bond formation, and N-glycosylation were positively correlated with the corresponding features of the four model proteins. Among others, oxidative folding enzymes showed the strongest association with disulfide bond formation, supporting their critical roles in proper folding and maintaining the ER stability. Knockdown of disulfide-isomerase PDIA4, a measured interactor with significance for SERPINC1 but not SERPINA1, led to the decreased secretion of SERPINC1, which relies on its extensive disulfide bonds, compared to SERPINA1, which has no disulfide bonds. Proximity-dependent labeling successfully identified the transient interactions supporting synthesis of secreted recombinant proteins and refined our understanding of key molecular mechanisms of the secretory pathway during recombinant protein production.
Topics: Glycosylation; HEK293 Cells; Humans; Protein Folding; Protein Interaction Maps; Protein Processing, Post-Translational; Protein Transport; Recombinant Proteins
PubMed: 33169829
DOI: 10.1002/bit.27621 -
Experimental Dermatology Mar 2016In addition to producing sebum, sebocytes link lipid metabolism with inflammation at a cellular level and hence, greatly resemble adipocytes. However, so far no analysis...
In addition to producing sebum, sebocytes link lipid metabolism with inflammation at a cellular level and hence, greatly resemble adipocytes. However, so far no analysis was performed to identify and characterize the adipocyte-associated inflammatory proteins, the members of the adipokine family in sebocytes. Therefore, we determined the expression profile of adipokines [adiponectin, interleukin (IL) 6, resistin, leptin, serpin E1, visfatin, apelin, chemerin, retinol-binding protein 4 (RBP4) and monocyte chemoattractant protein 1 (MCP1)] in sebaceous glands of healthy and various disease-affected (acne, rosacea, melanoma and psoriasis) skin samples. Sebaceous glands in all examined samples expressed adiponectin, IL6, resistin, leptin, serpin E1 and visfatin, but not apelin, chemerin, RBP4 and MCP1. Confirming the presence of the detected adipokines in the human SZ95 sebaceous gland cell line we further characterized their expression and secretion patterns under different stimuli mimicking bacterial invasion [by using Toll-like receptor (TLR)2 and 4 activators], or by 13-cis retinoic acid (13CRA; also known as isotretinoin), a key anti-acne agent. With the exception of resistin, the expression of all of the detected adipokines (adiponectin, IL6, leptin, serpin E1 and visfatin) could be further regulated at the level of gene expression, showing a close correlation with the secreted protein levels. Besides providing further evidence on similarities between adipocytes and sebocytes, our results strongly suggest that sebocytes are not simply targets of inflammation but may exhibit initiatory and modulatory roles in the inflammatory processes of the skin through the expression and secretion of adipokines.
Topics: Adipocytes; Adipokines; Adiponectin; Cell Line; Gene Expression Regulation; Humans; Inflammation; Interleukin-6; Leptin; Lipid Metabolism; Resistin; Sebaceous Glands; Sebum; Skin
PubMed: 26476096
DOI: 10.1111/exd.12879 -
Frontiers in Immunology 2020Most extracellular proteins are secreted via the classical endoplasmic reticulum (ER)/Golgi-dependent secretion pathway; however, some proteins, including a few... (Review)
Review
Most extracellular proteins are secreted via the classical endoplasmic reticulum (ER)/Golgi-dependent secretion pathway; however, some proteins, including a few danger-associated molecular patterns (DAMPs), are secreted via non-classical ER/Golgi-independent secretion pathways. The evolutionarily conserved high mobility group box1 (HMGB1) is a ubiquitous nuclear protein that can be released by almost all cell types. HMGB1 lacks signal peptide and utilizes diverse non-canonical secretion mechanisms for its extracellular export. Although the post-translational modifications of HMGB1 were demonstrated, the oxidation of HMGB1 and secretion mechanisms are not highlighted yet. We currently investigated that peroxiredoxins I and II (PrxI/II) induce the intramolecular disulfide bond formation of HMGB1 in the nucleus. Disulfide HMGB1 is preferentially transported out of the nucleus by binding to the nuclear exportin chromosome-region maintenance 1 (CRM1). We determined the kinetics of HMGB1 oxidation in bone marrow-derived macrophage as early as a few minutes after lipopolysaccharide treatment, peaking at 4 h while disulfide HMGB1 accumulation was observed within the cells, starting to secrete in the late time point. We have shown that HMGB1 oxidation status, which is known to determine the biological activity in extracellular HMGB1, is crucial for the secretion of HMGB1 from the nucleus. This review summarizes selected aspects of HMGB1 redox biology relevant to the induction and propagation of inflammatory diseases. We implicate the immunological significance and the need for novel HMGB1 inhibitors through mechanism-based studies.
Topics: Animals; HMGB1 Protein; Humans; Oxidation-Reduction; Protein Processing, Post-Translational; Protein Transport
PubMed: 32587593
DOI: 10.3389/fimmu.2020.01189 -
Journal of Insect Physiology Mar 2015The eusocial ants are unique in that females (queens) acquire and store sperm on a single mating flight early in adult life. This event largely determines the size...
The eusocial ants are unique in that females (queens) acquire and store sperm on a single mating flight early in adult life. This event largely determines the size (possibly millions of workers), longevity (possibly decades) and genetic variation of the colonies that queens found, but our understanding of the fundamental biology of ejaculate production, transfer and physiological function remains extremely limited. We studied the ejaculation process in the leafcutter ant Atta colombica and found that it starts with the appearance of a clear pre-ejaculatory fluid (PEF) at the tip of the endophallus that is followed by the joint expulsion of the remainder of accessory gland (AG) secretion, sperm, accessory testes (AT) secretion, and a small mating plug. PEF, AG secretion and AT secretion all contribute to sperm survival, but PEF and AG secretion also reduce the survival of sperm from other males. We show that PEF is produced in the AGs and is likely identical to AG secretion because protein-banding patterns of PEF and AG secretion were similar on 1D electrophoresis gels, but differed from the protein-banding pattern of AT secretion. We show that proteins in AG secretion are responsible for the incapacitation of rival sperm and infer that transfer of AG secretion prior to sperm may allow these components to interact with rival sperm, while at the same time providing a supportive biochemical environment for the arrival of own sperm.
Topics: Animals; Ants; Ejaculation; Genitalia, Male; Insect Proteins; Male; Semen; Spermatozoa
PubMed: 25702828
DOI: 10.1016/j.jinsphys.2015.02.006 -
Hua Xi Kou Qiang Yi Xue Za Zhi = Huaxi... Jun 2018Protein glycosylation is one of the most important protein post-translational modifications that can affect life activities by endowing the protein with various... (Review)
Review
Protein glycosylation is one of the most important protein post-translational modifications that can affect life activities by endowing the protein with various structural and functional features. Saliva is an easy-to-obtain, noninvasive body fluid that contains components originating from serum, gingival crevicular fluid, and oropharyngeal mucosae. In recent years, understanding of saliva has been constantly updated with the developments in related research. Studies have shown that salivary proteins can be used as diagnostic markers for certain diseases, and changes of protein glycosylation in saliva are generally considered to be related to many diseases. In this review, salivary protein glycosylation and its relationship with systemic and oral diseases were discussed.
Topics: Gingival Crevicular Fluid; Glycosylation; Humans; Mouth Diseases; Saliva; Salivary Proteins and Peptides
PubMed: 29984939
DOI: 10.7518/hxkq.2018.03.020