Editing Chitinase (section)

== Classification ==

# Endochitinases (EC 3.2.1.14) randomly split chitin at internal sites of the chitin microfibril, forming soluble, low molecular mass [[multimer]] products. The multimer products includes di-acetylchitobiose, chitotriose, and chitotetraose, with the dimer being the predominant product.<ref name=":0">{{cite journal | vauthors= Sahai AS, Manocha MS |date=1993-08-01|title=Chitinases of fungi and plants: their involvement in morphogenesis and host—parasite interaction | journal=FEMS Microbiology Reviews | volume = 11 | issue = 4 | pages = 317–338 | doi = 10.1111/j.1574-6976.1993.tb00004.x |s2cid=86267956 | doi-access= free }}</ref>
#Exochitinases have also been divided into two sub categories:
## Chitobiosidases ({{EnzExplorer|3.2.1.29}}) act on the non-reducing end of the chitin microfibril, releasing the dimer, di-acetylchitobiose, one by one from the chitin chain. Therefore, there is no release of [[monosaccharide]]s or [[oligosaccharide]]s in this reaction.<ref>{{Cite journal | vauthors = Harman GE | title=Chitinolytic Enzymes of ''Trichoderma harzianum'': Purification of Chitobiosidase and Endochitinase | journal=Phytopathology|volume=83|issue=3|pages=313|doi=10.1094/phyto-83-313 | year=1993 }}</ref>
## β-1,4- ''N''-acetylglucosaminidases ({{EnzExplorer|3.2.1.30}}) split the multimer products, such as di-acetylchitobiose, chitotriose, and chitotetraose, into monomers of [[N-Acetylglucosamine|''N''-acetylglucoseamine]] (GlcNAc).<ref name=":0" />
Chitinases were also classified based on the amino acid sequences, as that would be more helpful in understanding the evolutionary relationships of these enzymes to each other.<ref name="Patil_2000">{{cite journal | vauthors = Patil RS, Ghormade V, Deshpande MV | title = Chitinolytic enzymes: an exploration | journal = Enzyme and Microbial Technology | volume = 26 | issue = 7 | pages = 473–483 | date = April 2000 | pmid = 10771049 | doi = 10.1016/s0141-0229(00)00134-4 | name-list-style = vanc }}</ref> Therefore, the chitinases were grouped into three [[Glycoside hydrolase families|families]]: [[Glycoside hydrolase family 18|18]], [[Glycoside hydrolase family 19|19]], and [[Glycoside hydrolase family 20|20]].<ref>{{cite journal | vauthors = Henrissat B | title = A classification of glycosyl hydrolases based on amino acid sequence similarities | journal = The Biochemical Journal | volume = 280 ( Pt 2) | issue = 2 | pages = 309–16 | date = December 1991 | pmid = 1747104 | pmc = 1130547 | doi = 10.1042/bj2800309 }}</ref> Both families 18 and 19 consists of endochitinases from a variety of different organisms, including viruses, bacteria, fungi, insect, and plants. However, family 19 mainly comprises plant chitinases. Family 20 includes ''N-''acetylglucosaminidase and a similar enzyme, [[N-acetylhexosaminidase|''N''-acetylhexosaminidase]].<ref name="Patil_2000" />

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|isoelectric pH]], [[signal peptide]], and [[inducer]]s.<ref name="Patil_2000" />

{{visible anchor|Class I}} chitinases had a cysteine-rich ''N''-terminal, leucine- or valine-rich signal peptide, and [[Vacuole|vacuolar]] localization. And then, Class I chitinases were further subdivided based on their acidic or basic nature into {{visible anchor|Class Ia}} and {{visible anchor|Class Ib}}, respectively.<ref>{{Cite journal | vauthors = Flach J, Pilet PE, Jollès P | date = August 1992 | title=What's new in chitinase research? | journal = Experientia | volume=48|issue=8|pages=701–716|doi=10.1007/BF02124285 | pmid = 1516675 | s2cid = 37362071 }}</ref> Class 1 chitinases were found to comprise only plant chitinases and mostly endochitinases.

{{visible anchor|Class II}} 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.<ref name="Patil_2000" />

{{visible anchor|Class III}} chitinases did not have similar sequences to chitinases in Class I or Class II.<ref name="Patil_2000" />

{{visible anchor|Class IV}} chitinases had similar characteristics, including the immunological properties, as Class I chitinases.<ref name="Patil_2000" /> However, Class IV chitinases were significantly smaller in size compared to Class I chitinases.<ref>{{cite journal | vauthors = Collinge DB, Kragh KM, Mikkelsen JD, Nielsen KK, Rasmussen U, Vad K | title = Plant chitinases | journal = The Plant Journal | volume = 3 | issue = 1 | pages = 31–40 | date = January 1993 | pmid = 8401605 | doi = 10.1046/j.1365-313x.1993.t01-1-00999.x | name-list-style = vanc | doi-access = free }}</ref>

{{visible anchor|Class V}} and {{visible anchor|Class VI}} 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.<ref name="Patil_2000" />[[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]]