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Chitinases (, chitodextrinase, 1,4-β-poly-N-acetylglucosaminidase, poly-β-glucosaminidase, β-1,4-poly-N-acetyl glucosamidinase, poly1,4-(N-acetyl-β-D-glucosaminide) glycanohydrolase, (1→4)-2-acetamido-2-deoxy-β-D-glucan glycanohydrolase; systematic name (1→4)-2-acetamido-2-deoxy-β-D-glucan glycanohydrolase) are hydrolytic that break down in chitin. (1999). 9783764358150, Birkhäuser. ISBN 9783764358150 They catalyse the following reaction:
As chitin is a component of the of fungi and exoskeleton elements of some animals (including and ), chitinases are generally found in organisms that either need to reshape their own chitin or dissolve and digest the chitin of fungi or animals.
Fungi, such as Coccidioides immitis, also possess degradative chitinases related to their role as detritivores and also to their potential as arthropod pathogens.
Chitinases are also present in plants – for example barley seed chitinase: , . Barley seeds are found to produce clone 10 in Ignatius et al 1994(a). They find clone 10, a Class I chitinase, in the seed aleurone during development. Leaves produce several (as well as several of β-1,3-glucanase). Ignatius et al 1994(b) find these in the leaves, induced by powdery mildew. Ignatius et al also find these (seed and leaf isozymes) to differ from each other. . Some of these are pathogenesis related (PR) proteins that are induced as part of systemic acquired resistance. Expression is mediated by the NPR1 gene and the salicylic acid pathway, both involved in resistance to fungal and insect attack. Other plant chitinases may be required for creating fungal symbioses.
Although mammals do not produce chitin, they have two functional chitinases, Chitotriosidase (CHIT1) and acidic mammalian chitinase (AMCase), as well as chitinase-like proteins (such as YKL-40) that have high sequence similarity but lack chitinase activity.
And as the gene sequences of the chitinases were known, they were further classified into six classes based on their sequences. Characteristics that determined the classes of chitinases were the N-terminal sequence, localization of the enzyme, Isoelectric Ph, signal peptide, and .
chitinases had a cysteine-rich ''N''-terminal, leucine- or valine-rich signal peptide, and [[vacuolar|Vacuole]] localization. And then, Class I chitinases were further subdivided based on their acidic or basic nature into and , respectively. Class 1 chitinases were found to comprise only plant chitinases and mostly endochitinases.
chitinases did not have the cysteine-rich ''N''-terminal but had a similar sequence to Class I chitinases. Class II chitinases were found in plants, fungi, and bacteria and mostly consisted of exochitinases.
chitinases did not have similar sequences to chitinases in Class I or Class II.
chitinases had similar characteristics, including the immunological properties, as Class I chitinases. However, Class IV chitinases were significantly smaller in size compared to Class I chitinases.
and chitinases are not well characterized. However, one example of a Class V chitinase showed two chitin [[binding domain]]s in tandem, and based on the gene sequence, the cysteine-rich ''N''-terminal seemed to have been lost during evolution, probably due to less selection pressure that caused the catalytic domain to lose its function.[[File:Endochitinase.png|thumb|679x679px|Endochitinase breaking down chitin into multimer products.|center]][[File:Exochitinase.png|thumb|697x697px|Exochitinase breaking down chitin into dimers via chitobiosidase and monomers via β-1,4-''N''-acetylglucosaminidase.|center]]
Chitinase activity can also be detected in human blood and possibly cartilage. As in plant chitinases this may be related to pathogen resistance.
Human chitinases may explain the link between some of the most common allergies (, mold spores—both of which contain chitin) and worm (helminth) infections, as part of one version of the hygiene hypothesis (worms have chitinous mouthparts to hold the intestinal wall). Finally, the link between chitinases and salicylic acid in plants is well established—but there is a hypothetical link between salicylic acid and allergies in humans.
May be used to monitor enzymotherapy supplementation in Gaucher's disease.[1]
The regulation of an endochitinase in Trichoderma atroviride is dependent on a N-acetylglucosaminidase, and the data indicates a feedback-loop where the break down of chitin produces N-acetylglucosamine, which would be possibly taken up and triggers up-regulation of the chitinbiosidases.
In Saccharomyces cerevisiae and the regulation of ScCts1p ( S. cerevisiae chitinase 1), one of the chitinases involved in cell separation after cytokinesis by degrading the chitin of the primary septum. As these types of chitinases are important in cell division, there must be tight regulation and activation. Specifically, Cts1 expression has to be activated in daughter cells during late mitosis and the protein has to localize at the daughter site of the septum. And to do this, there must be coordination with other networks controlling the different phases of the cell, such as Cdc14 Early Anaphase Release (FEAR), Mitotic exit, and regulation of Ace2p (transcription factor) and cellular morphogenesis (RAM) signalling networks. Overall, the integration of the different regulatory networks allows for the cell wall degrading chitinase to function dependent on the cell's stage in the cell cycle and at specific locations among the daughter cells.
Some parts of chitinase molecules, almost identical in structure to hevein or other proteins in rubber latex due to their similar function in plant defense, may trigger an allergic cross-reaction known as latex-fruit syndrome.
Possible future applications of chitinases are as food additives to increase shelf life, therapeutic agent for asthma and chronic rhinosinusitis, as an anti-fungal remedy, an anti-tumor drug and as a general ingredient to be used in protein engineering.
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