definición y significado de secretion | sensagent.com


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alemán árabe búlgaro checo chino coreano croata danés eslovaco esloveno español estonio farsi finlandés francés griego hebreo hindù húngaro indonesio inglés islandés italiano japonés letón lituano malgache neerlandés noruego polaco portugués rumano ruso serbio sueco tailandès turco vietnamita

Definición y significado de secretion

Definición

secretion (n.)

1.a functionally specialized substance (especially one that is not a waste) released from a gland or cell

2.the organic process of synthesizing and releasing some substance

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Merriam Webster

SecretionSe*cre"tion (?), n. [L. secretio: cf. F. sécrétion.]
1. The act of secreting or concealing; as, the secretion of dutiable goods.

2. (Physiol.) The act of secreting; the process by which material is separated from the blood through the agency of the cells of the various glands and elaborated by the cells into new substances so as to form the various secretions, as the saliva, bile, and other digestive fluids. The process varies in the different glands, and hence are formed the various secretions.

3. (Physiol.) Any substance or fluid secreted, or elaborated and emitted, as the gastric juice.

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Definición (más)

definición de secretion (Wikipedia)

Sinónimos

secretion (n.)

discharge, emission, secernment

Ver también

secretion (n.)

release, secrete, secretory

Frases

Abnormal secretion of gastrin • Ectopic hormone secretion, not elsewhere classified • Inappropriate ACTH Secretion Syndrome • Inappropriate FSH Secretion Syndrome • Inappropriate GH Secretion Syndrome (Acromegaly) • Inappropriate LH Secretion Syndrome • Inappropriate TSH Secretion Syndrome • Increased secretion from endocrine pancreas of growth hormone-releasing hormone • Increased secretion from endocrine pancreas of pancreatic polypeptide • Increased secretion from endocrine pancreas of somatostatin • Increased secretion from endocrine pancreas of vasoactive-intestinal polypeptide • Increased secretion of glucagon • increased secretion from endocrine pancreas of growth hormone-releasing hormone • increased secretion of glucagon • internal secretion • lachrymal secretion • lacrimal secretion • mucous secretion

Diccionario analógico

Wikipedia

Secretion

                   

Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product.

Secretion in bacterial species means the transport or translocation of effector molecules for example proteins, enzymes or toxins (such as cholera toxin in pathogenic bacteria for example Vibrio cholerae) from across the interior (cytoplasm or cytosol) of a bacterial cell to its exterior. Secretion is a very important mechanism in bacterial functioning and operation in their natural surrounding environment for adaptation and survival.

Contents

  Secretion in eukaryotic cells

  Mechanism

Eukaryotic cells, including human cells, have a highly evolved process of secretion. Proteins targeted for the outside are synthesized by ribosomes docked to the rough endoplasmic reticulum (ER). As they are synthesized, these proteins translocate into the ER lumen, where they are glycosylated and where molecular chaperones aid protein folding. Misfolded proteins are usually identified here and retrotranslocated by ER-associated degradation to the cytosol, where they are degraded by a proteasome. The vesicles containing the properly-folded proteins then enter the Golgi apparatus.

In the Golgi apparatus, the glycosylation of the proteins is modified and further posttranslational modifications, including cleavage and functionalization, may occur. The proteins are then moved into secretory vesicles which travel along the cytoskeleton to the edge of the cell. More modification can occur in the secretory vesicles (for example insulin is cleaved from proinsulin in the secretory vesicles).

Eventually, there is vesicle fusion with the cell membrane at a structure called the porosome, in a process called exocytosis, dumping its contents out of the cell's environment.[1]

Strict biochemical control is maintained over this sequence by usage of a pH gradient: the pH of the cytosol is 7.4, the ER's pH is 7.0, and the cis-golgi has a pH of 6.5. Secretory vesicles have pHs ranging between 5.0 and 6.0; some secretory vesicles evolve into lysosomes, which have a pH of 4.8.

  Nonclassical secretion

There are many proteins like FGF1 (aFGF), FGF2 (bFGF), interleukin1 (IL1) etc. which do not have a signal sequence. They do not use the classical ER-golgi pathway. These are secreted through various nonclassical pathways.

At least four nonclassical (unconventional) protein secretion pathways have been described.[2] They include 1) direct translocation of proteins across the plasma membrane likely through membrane transporters, 2) blebbing, 3) lysosomal secretion, and 4) release via exosomes derived from multivesicular bodies. In addition, proteins can be released from cells by mechanical or physiological wounding[3] and through nonlethal, transient oncotic pores in the plasma membrane induced by washing cells with serum-free media or buffers.[4]

  Secretion in human tissues

Many human cell types have the ability to be secretory cells. They have a well-developed endoplasmic reticulum and Golgi apparatus to fulfill their function. Tissues in humans that produce secretions include the gastrointestinal tract which secretes digestive enzymes and gastric acid, the lung which secretes surfactants, and sebaceous glands which secrete sebum to lubricate the skin and hair. Meibomian glands in the eyelid secrete sebum to lubricate and protect the eye.

  Secretion in Gram negative bacteria

Secretion is not unique to eukaryotes alone, it is present in bacteria and archaea as well. ATP binding cassette (ABC) type transporters are common to all the three domains of life. The Sec system constituting the Sec Y-E-G complex (see Type II secretion system (T2SS), below) is another conserved secretion system, homologous to the translocon in the eukaryotic endoplasmic reticulum and the Sec 61 translocon complex of yeast. Some secreted proteins are translocated across the cytoplasmic membrane by the Sec translocon, which requires the presence of an N-terminal signal peptide on the secreted protein. Others are translocated across the cytoplasmic membrane by the twin-arginine translocation pathway (Tat). Gram negative bacteria have two membranes, thus making secretion topologically more complex. There are at least six specialized secretion systems in Gram negative bacteria. Many secreted proteins are particularly important in bacterial pathogenesis.[5]

  Type I secretion system (T1SS or TOSS)

T1SS.svg

It is similar to the ABC transporter, however it has additional proteins that, together with the ABC protein, form a contiguous channel traversing the inner and outer membranes of Gram-negative bacteria. It is a simple system, which consists of only three protein subunits: the ABC protein, membrane fusion protein (MFP), and outer membrane protein (OMP). Type I secretion system transports various molecules, from ions, drugs, to proteins of various sizes (20 - 900 kDa). The molecules secreted vary in size from the small Escherichia coli peptide colicin V, (10 kDa) to the Pseudomonas fluorescens cell adhesion protein LapA of 900 kDa. The best characterized are the RTX toxins and the lipases. Type I secretion is also involved in export of non-proteinaceous substrates like cyclic β-glucans and polysaccharides.

T2SS.svg

  Type II secretion system (T2SS)

Proteins secreted through the type II system, or main terminal branch of the general secretory pathway, depend on the Sec or Tat system for initial transport into the periplasm. Once there, they pass through the outer membrane via a multimeric (12-14 subunits) complex of pore forming secretin proteins. In addition to the secretin protein, 10-15 other inner and outer membrane proteins compose the full secretion apparatus, many with as yet unknown function. Gram-negative type IV pili use a modified version of the type II system for their biogenesis, and in some cases certain proteins are shared between a pilus complex and type II system within a single bacterial species.

  Type III secretion system (T3SS or TTSS)

T3SS.svg

It is homologous to bacterial flagellar basal body. It is like a molecular syringe through which a bacterium (e.g. certain types of Salmonella, Shigella, Yersinia, Vibrio) can inject proteins into eukaryotic cells. The low Ca2+ concentration in the cytosol opens the gate that regulates T3SS. One such mechanism to detect low calcium concentration has been illustrated by the lcrV (Low Calcium Response) antigen utilized by Yersinia pestis, which is used to detect low calcium concentrations and elicits T3SS attachment. The Hrp system in plant pathogens inject harpins through similar mechanisms into plants. This secretion system was first discovered in Yersinia pestis and showed that toxins could be injected directly from the bacterial cytoplasm into the cytoplasm of its host's cells rather than simply be secreted into the extracellular medium.[6]

T4SS.svg

  Type IV secretion system (T4SS or TFSS)

It is homologous to conjugation machinery of bacteria (and archaeal flagella). It is capable of transporting both DNA and proteins. It was discovered in Agrobacterium tumefaciens, which uses this system to introduce the T-DNA portion of the Ti plasmid into the plant host, which in turn causes the affected area to develop into a crown gall (tumor). Helicobacter pylori uses a type IV secretion system to deliver CagA into gastric epithelial cells, which is assicated with gastric carcinogenesis.[7] Bordetella pertussis, the causative agent of whooping cough, secretes the pertussis toxin partly through the type IV system. Legionella pneumophila, the causing agent of legionellosis (Legionnaires' disease) utilizes type IV secretion system, known as the icm/dot (intracellular multiplication / deffect in organelle trafficking genes) system, to translocate numerous effector proteins into its eukaryotic host.[8] The prototypic Type IV secretion system is the VirB complex of Agrobacterium tumefaciens.[9]

  Type V secretion system (T5SS)

T5SS.svg

Also called the autotransporter system,[10] type V secretion involves use of the Sec system for crossing the inner membrane. Proteins which use this pathway have the capability to form a beta-barrel with their C-terminus which inserts into the outer membrane, allowing the rest of the peptide (the passenger domain) to reach the outside of the cell. Often, autotransporters are cleaved, leaving the beta-barrel domain in the outer membrane and freeing the passenger domain. Some people believe remnants of the autotransporters gave rise to the porins which form similar beta-barrel structures.

  Type VI secretion system (T6SS)

Type VI secretion systems have been identified in 2006 by the group of John Mekalanos at the Harvard Medical School (Boston, USA) in two bacterial pathogens, Vibrio cholerae and Pseudomonas aeruginosa.[11][12] Since then, Type VI secretion systems have been found in most genomes of proteobacteria, including animal, plant, human pathogens, as well as soil, environmental or marine bacteria.[13][14] While most of the early studies of Type VI secretion focused on its role in the pathogenesis of higher organisms, more recent studies suggested a broader physiological role in defense against simple eukaryotic predators and its role in inter-bacteria interactions.[15] The Type VI secretion system gene clusters contain from 15 to more than 20 genes, two of which, Hcp and VgrG, have been shown to be nearly universally secreted substrates of the system. Structural analysis of these and other proteins in this system bear a striking resemblance to the tail spike of the T4 phage.[16]

  Release of outer membrane vesicles

In addition to the use of the multiprotein complexes listed above, Gram-negative bacteria possess another method for release of material: the formation of outer membrane vesicles.[17] Portions of the outer membrane pinch off, forming spherical structures made of a lipid bilayer enclosing periplasmic materials. Vesicles from a number of bacterial species have been found to contain virulence factors, some have immunomodulatory effects, and some can directly adhere to and intoxicate host cells. While release of vesicles has been demonstrated as a general response to stress conditions, the process of loading cargo proteins seems to be selective.[18]

  Secretion in Gram positive bacteria

Proteins with appropriate N-terminal targeting signals are synthesized in the cytoplasm and then directed to a specific protein transport pathway. During, or shortly after its translocation across the cytoplasmic membrane, the protein is processed and folded into its active form. Then the translocated protein is either retained at the extracytoplasmic side of the cell or released into the environment. Since the signal peptides that target proteins to the membrane are key determinants for transport pathway specificity, these signal peptides are classified according to the transport pathway to which they direct proteins. Signal peptide classification is based on the type of signal peptidase (SPase) that is responsible for the removal of the signal peptide. The majority of exported proteins are exported from the cytoplasm via the general Secretory (Sec) pathway. Most well known virulence factors (e.g. exotoxins of Staphylococcus aureus, protective antigen of Bacillus anthracis, listeriolysin O of Listeria monocytogenes) that are secreted by Gram-positive pathogens have a typical N-terminal signal peptide that would lead them to the Sec-pathway. Proteins that are secreted via this pathway are translocated across the cytoplasmic membrane in an unfolded state. Subsequent processing and folding of these proteins takes place in the cell wall environment on the trans-side of the membrane. In some Staphylococcus and Streptococcus species, the accessory secretory system handles the export of highly repetitive adhesion glycoproteins. In addition to the Sec and accessory-Sec systems, some Gram-positive bacteria contain the Tat-system that is able to translocate folded proteins across the membrane. This is especially appropriate for proteins that need co-factors, such as iron-sulfur clusters and molybdopterin, which are incorporated in the cytoplasm. Pathogenic bacteria may contain certain special purpose export systems that are specifically involved in the transport of only a few proteins. For example, several gene clusters have been identified in mycobacteria that encode proteins that are secreted into the environment via specific pathways (ESAT-6) and are important for mycobacterial pathogenesis. Specific ATP-binding cassette (ABC) transporters direct the export and processing of small antibacterial peptides called bacteriocins. Genes for endolysins that are responsible for the onset of bacterial lysis are often located near genes that encode for holin-like proteins, suggesting that these holins are responsible for endolysin export to the cell wall.[5]

  See also

  References

  1. ^ Anderson LL (2006). "Discovery of the 'porosome'; the universal secretory machinery in cells". J. Cell. Mol. Med. 10 (1): 126–31. DOI:10.1111/j.1582-4934.2006.tb00294.x. PMID 16563225. http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=1582-1838&date=2006&volume=10&issue=1&spage=126. 
  2. ^ Nickel, Walter; Matthias Seedorf (2008). "Unconventional mechanisms of protein transport to the cell surface of eukaryotic cells". Annu. Rev. Cell Dev. Biol. 24: 287–308. 
  3. ^ McNeil, Paul; Richard A. Steinhardt (2003). "Plasma membrane disruption: Repair, prevention, adaptation". Annu. Rev. Cell Dev. Biol. 19: 697–731. 
  4. ^ Chirico, William (2011). "Protein release through nonlethal oncotic pores as an alternative nonclassical secretory pathway". BMC Cell Biology 12: 46. http://www.biomedcentral.com/1471-2121/12/46. 
  5. ^ a b Wooldridge K (editor) (2009). Bacterial Secreted Proteins: Secretory Mechanisms and Role in Pathogenesis. Caister Academic Press. ISBN 978-1-904455-42-4. 
  6. ^ Salyers, A. A. & Whitt, D. D. (2002). Bacterial Pathogenesis: A Molecular Approach, 2nd ed., Washington, D.C.: ASM Press. ISBN 1-55581-171-X
  7. ^ Hatakeyama, M. & Higashi, H. (2005). "Helicobacter pylori CagA: a new paradigm for bacterial carcinogenesis". Cancer Science 96: 835–843. DOI:10.1111/j.1349-7006.2005.00130.x. PMID 16367902. 
  8. ^ Cascales E & Christie P.J. (2003). "The versatile Type IV secretion systems". Nat Rev Microbiol 1 (2): 137–149. DOI:10.1038/nrmicro753. PMID 15035043. 
  9. ^ Christie PJ, Atmakuri K, Jabubowski S, Krishnamoorthy V & Cascales E. (2005). "Biogenesis, architecture, and function of bacterial Type IV secretion systems". Ann Rev Microbiol 59: 451–485. DOI:10.1146/annurev.micro.58.030603.123630. PMID 16153176. 
  10. ^ Thanassi, D.G.; Stathopoulos, C.; Karkal, A.; Li, H. (2005). "Protein secretion in the absence of ATP: the autotransporter, two-partner secretion and chaperone/usher pathways of Gram-negative bacteria (Review)". Molecular Membrane Biology 22 (1): 63–72. DOI:10.1080/09687860500063290. 
  11. ^ Pukatzki S, Ma AT, Sturtevant D, Krastins B, Sarracino D, Nelson WC, Heidelberg JF, Mekalanos JJ (2006). "Identification of a conserved bacterial protein secretion system in Vibrio cholerae using the Dictyostelium host model system". Proc. Natl. Acad. Sci. U.S.A. 103 (5): 1528–33. DOI:10.1073/pnas.0510322103. PMC 1345711. PMID 16432199. //www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1345711. 
  12. ^ Mougous JD, Cuff ME, Raunser S, Shen A, Zhou M, Gifford CA, Goodman AL, Joachimiak G, Ordoñez CL, Lory S, Walz T, Joachimiak A, Mekalanos JJ (2006). "A Virulence Locus of Pseudomonas aeruginosa Encodes a Protein Secretion Apparatus". Science 312 (5779): 1526–30. DOI:10.1126/science.1128393. PMC 2800167. PMID 16763151. //www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2800167. 
  13. ^ Bingle LEH, Bailey CM, Pallen MJ (2008). "Type VI secretion: a beginner's guide". Curr. Opin. Microbiol. 11 (1): 3–8. DOI:10.1016/j.mib.2008.01.006. PMID 18289922. 
  14. ^ Cascales E (2008). "The type VI secretion toolkit". EMBO Reports 9 (8): 735–741. DOI:10.1038/embor.2008.131. PMC 2515208. PMID 18617888. //www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2515208. 
  15. ^ Schwarz S; Hood RD; Mougus JD (Dec 2010). Trends in Microbiology 18 (12): 531–537. DOI:10.1016/j.tim.2010.09.001. http://www.sciencedirect.com/science/article/pii/S0966842X10001654. 
  16. ^ Leiman PG; Basler M; Ramagopal UA; Bonanno JB; Sauder JM; Pukatzki S; Burley SK; Almo SC; Mekalanos JJ (March 2009). "Type VI secretion apparatus and phage tail-associated protein complexes share a common evolutionary origin.". Proceedings of the National Academy of Sciences of the United States of America 106 (11): 4154–4159. DOI:10.1073/pnas.0813360106. PMC 2657435. PMID 19251641. //www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2657435. 
  17. ^ Chatterjee, SN and J Das. "Electron microscopic observations on the excretion of cell wall material by Vibrio cholerae." "J.Gen.Microbiol." "49" : 1-11 (1967) ; Kuehn, MJ and NC Kesty. "Bacterial outer membrane vesicles and the host-pathogen interaction." Genes Dev. 19(22):2645-55 (2005)
  18. ^ McBroom, AJ and MJ Kuehn "Release of outer membrane vesicles by Gram-negative bacteria is a novel envelope stress response." Mol. Microbiol. 63(2):545-58 (2007)

  Bibliography

  • Molecular Biology of the Cell 4th edition - Alberts et al.
  • The Physiology and Biochemistry of Prokaryotes 2nd edition – David White
  • Cellsalive.com-David Avon

  External links

   
               

 

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