Exoenzyme

Source: Wikipedia, the free encyclopedia.
(Redirected from
Ectoenzyme
)
Organelles of the secretory pathway involved in the secretion of exoenzymes

An exoenzyme, or extracellular enzyme, is an

pathogenic species also use exoenzymes as virulence factors to assist in the spread of these disease-causing microorganisms.[3] In addition to the integral roles in biological systems, different classes of microbial exoenzymes have been used by humans since pre-historic times for such diverse purposes as food production, biofuels, textile production and in the paper industry.[4] Another important role that microbial exoenzymes serve is in the natural ecology and bioremediation of terrestrial and marine[5]
environments.

History

Very limited information is available about the original discovery of exoenzymes. According to Merriam-Webster dictionary, the term "exoenzyme" was first recognized in the English language in 1908.[6] The book "Intracellular Enzymes: A Course of Lectures Given in the Physiological," by Horace Vernon is thought to be the first publication using this word in that year.[7] Based on the book, it can be assumed that the first known exoenzymes were pepsin and trypsin, as both are mentioned by Vernon to have been discovered by scientists Briike and Kiihne before 1908.[8]

Function

In

fungi, exoenzymes play an integral role in allowing the organisms to effectively interact with their environment. Many bacteria use digestive enzymes to break down nutrients in their surroundings. Once digested, these nutrients enter the bacterium, where they are used to power cellular pathways with help from endoenzymes.[9]

Many exoenzymes are also used as

type three secretion system.[10] With either process, pathogens can attack the host cell's structure and function, as well as its nucleic DNA.[11]

In

macronutrients via hydrolysis. Breakdown of these nutrients allows for their incorporation into other metabolic pathways.[13]

Examples of exoenzymes as virulence factors

Source:[3]

Microscopic view of necrotizing fasciitis as caused by Streptococcus pyogenes

Necrotizing enzymes

Necrotizing enzymes destroy cells and tissue. One of the best known examples is an exoenzyme produced by Streptococcus pyogenes that causes necrotizing fasciitis
in humans.

Coagulase

By binding to

defense mechanisms
.

Fibrin layer formed by Staphyloccocus aureus

Kinases

The opposite of coagulase, kinases can dissolve clots. S. aureus can also produce staphylokinase, allowing them to dissolve the clots they form, to rapidly diffuse into the host at the correct time.[14]

Hyaluronidase

Similar to collagenase, hyaluronidase enables a pathogen to penetrate deep into tissues. Bacteria such as Clostridium do so by using the enzyme to dissolve collagen and hyaluronic acid, the protein and saccharides, respectively, that hold tissues together.

Hemolysins

beta-hemolytic, or gamma
-hemolytic (non-hemolytic).

Examples of digestive exoenzymes

Amylases

Pancreatic alpha-amylase 1HNY

hydrolyze glucose molecules from the ends of amylose and amylopectin.[17] Amylases are critically important extracellular enzymes and are found in plants, animals, and microorganisms. In humans, amylases are secreted by the pancreas and salivary glands, with both sources of the enzyme required for complete starch hydrolysis.[18]

Lipoprotein lipase

cardiac, and muscle.[19] Lipoprotein lipase is downregulated by high levels of insulin,[20] and upregulated by high levels of glucagon and adrenaline.[19]

Pectinase

fungi and bacteria.[23] Pectinases are most often used to break down
the pectic elements found in plants and plant-derived products.

Pepsin

Discovered in 1836,

eggs.[24] Pepsin works best at the pH of gastric acid, 1.5 to 2.5, and is deactivated when the acid is neutralized to a pH of 7.[24]

Trypsin

Also one of the first exoenzymes to be discovered,

enterokinase to form active trypsin. Due to its role in the small intestine, trypsin works at an optimal pH of 8.0.[28]

Bacterial assays

Amylase test results
Lipase test results
Results of bacterial assays. Left:amylase bacterial assay on a starch medium. A indicates a positive result, D indicates a negative result. Right: lipase bacterial assay on an olive oil medium. 1 shows a positive result, 3 shows a negative result

The production of a particular digestive exoenzyme by a bacterial cell can be assessed using plate assays. Bacteria are streaked across the agar, and are left to incubate. The release of the enzyme into the surroundings of the cell cause the breakdown of the macromolecule on the plate. If a reaction does not occur, this means that the bacteria does not create an exoenzyme capable of interacting with the surroundings. If a reaction does occur, it becomes clear that the bacteria does possess an exoenzyme, and which macromolecule is hydrolyzed determines its identity.[2]

Amylase

Amylase breaks down carbohydrates into mono- and disaccharides, so a starch agar must be used for this assay. Once the bacteria is streaked on the agar, the plate is flooded with iodine. Since iodine binds to starch but not its digested by-products, a clear area will appear where the amylase reaction has occurred. Bacillus subtilis is a bacterium that results in a positive assay as shown in the picture.[2]

Lipase

Lipase assays are done using a

Staphylococcus epidermis results in a positive lipase assay.[2]

Biotechnological and industrial applications

bacterial strains or a consortium that work to facilitate the breakdown of cellulose materials into ethanol by secreting exoenzymes such as cellulases and laccases.[29] In addition to the important role it plays in biofuel production, xylanase is utilized in a number of other industrial and biotechnology applications due to its ability to hydrolyze cellulose and hemicellulose. These applications include the breakdown of agricultural and forestry wastes, working as a feed additive to facilitate greater nutrient uptake by livestock, and as an ingredient in bread making to improve the rise and texture of the bread.[30]

Generic Biodiesel Reaction. Lipases can serve as a biocatalyst in this reaction

methyl- and other short-chain alcohol esters by a single transesterification reaction.[32]

recycled fibers, modify coarse mechanical pulp, and for the partial or complete hydrolysis of pulp fibers.[33]
Cellulases and hemicellulases are used in these industrial applications due to their ability to hydrolyze the cellulose and hemicellulose components found in these materials.

Bioremediation applications

Water pollution from runoff of soil and fertilizer

hazardous pollutants is mostly carried out by naturally occurring or purposely introduced microorganisms that are capable of breaking down or absorbing the desired pollutant. The types of pollutants that are often the targets of bioremediation strategies are petroleum products (including oil and solvents) and pesticides.[34] In addition to the microorganisms ability to digest and absorb the pollutants, their secreted exoenzymes play an important role in many bioremediation strategies.[35]

oxidize many pollutants. Some of the pollutants that laccases have been used to treat include dye-containing effluents from the textile industry, wastewater pollutants (chlorophenols, PAHs, etc.), and sulfur-containing compounds from coal processing.[36]

Exocytic vesicles move along actin microfilaments toward the fungal hyphal tip where they release their contents including exoenzymes

Gram-negative bacterium, Comamonas acidovorans, that was capable of degrading polyurethane waste in the environment.[37] Cell-free use of microbial exoenzymes as agents of bioremediation is also possible although their activity is often not as robust and introducing the enzymes into certain environments such as soil has been challenging.[37] In addition to terrestrial based microorganisms, marine based bacteria and their exoenzymes show potential as candidates in the field of bioremediation. Marine based bacteria have been utilized in the removal of heavy metals, petroleum/diesel degradation and in the removal of polyaromatic hydrocarbons among others.[38]

References

  1. PMID 18577009
    .
  2. ^ a b c d Roberts, K. "Exoenzymes". Prince George's Community College. Archived from the original on 13 June 2013. Retrieved 8 December 2013.
  3. ^
    ISBN 9781605476735.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  4. ^
    ISBN 9781402092121. {{cite book}}: |first= has generic name (help)CS1 maint: multiple names: authors list (link
    )
  5. PMID 21329211
    .
  6. ^ "Merriam-Webster". Retrieved 2013-10-26.
  7. ^ "Lexic.us". Retrieved 2013-10-26.
  8. ^ a b Vernon, Horace. "Intracellular Enzymes: A Course of Lectures Given in the Physiological". Retrieved 2013-10-26.
  9. ^ Kaiser, Gary. "Lab 8: Identification of Bacteria Through Biochemical Testing". Biol 230 Lab Manual. Archived from the original on 11 December 2013. Retrieved 9 December 2013.
  10. PMID 20926516
    .
  11. PMID 10377131
    .
  12. ISBN 978-0716776017
    .
  13. ^ Andrews, Lary. "Supplemental Enzymes for Digestion". Health and Healing Research. Archived from the original on 27 July 2013. Retrieved 9 December 2013.
  14. ^ Todar, Kenneth. "Mechanisms of Bacterial Pathogenicity". Todar's Online Textbook of Bacteriology. Kenneth Todar, PhD. Retrieved 12 December 2013.
  15. S2CID 253807898
    .
  16. doi:10.1016/j.procbio.2012.12.018
    .
  17. PMID 10744959
    .
  18. PMID 21634067
    . Retrieved 25 November 2013.
  19. ^
    S2CID 40089672
    .
  20. PMID 2677048
    .
  21. doi:10.1016/j.procbio.2005.03.026
    .
  22. doi:10.1016/j.procbio.2011.05.010
    .
  23. doi:10.1016/S0032-9592(02)00203-0
    .
  24. ^ a b c "Encyclopædia Britannica". Retrieved November 14, 2013.
  25. PMID 6785873
    .
  26. ^ a b Worthington, Krystal. "Trypsin". Worthington Biochemical Corporation. Retrieved 26 November 2013.
  27. ^ "Trypsin". Free Dictionary. Retrieved 26 November 2013.
  28. ^ "Trypsin Product Information". Worthington Biochemical Corporation. Retrieved 26 November 2013.
  29. ^
    S2CID 7785046
    .
  30. PMID 22138412
    .
  31. ^
    PMID 12323363
    .
  32. PMID 22426735
    .
  33. ^
    PMID 14538100
    .
  34. ^ "A Citizen's Guide to Bioremediation". United States Environmental Protection Agency. September 2012. Retrieved 5 December 2013.
  35. PMID 21912739
    .
  36. ^
    S2CID 24676340
    .
  37. ^
    doi:10.1016/j.enzmictec.2004.05.006
    .
  38. S2CID 253773148
    .
Retrieved from "https://en.wikipedia.org/w/index.php?title=Exoenzyme&oldid=1215159462"