Chitinase

Chitinivorous organisms include many bacteria (Aeromonads, Bacillus, Vibrio, among others), which may be pathogenic or detritivorous. They attack living arthropods, zooplankton or fungi or they may degrade the remains of these organisms. 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 isozymes (as well as several of β-1,3-glucanase). Ignatius et al 1994(b) find these in the leaves, induced by powdery mildew. 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. == 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. • Exochitinases have also been divided into two sub categories: • Chitobiosidases () 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 monosaccharides or oligosaccharides in this reaction. • β-1,4- N-acetylglucosaminidases () split the multimer products, such as di-acetylchitobiose, chitotriose, and chitotetraose, into monomers of N-acetylglucoseamine (GlcNAc). Therefore, the chitinases were grouped into three families: 18, 19, and 20. 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. 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. and chitinases are not well characterized. However, one example of a Class V chitinase showed two chitin binding domains 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. == Function ==

Like cellulose, chitin is an abundant biopolymer that is relatively resistant to degradation. Many mammals can digest chitin and the specific chitinase levels in vertebrate species are adapted to their feeding behaviours. Certain fish are able to digest chitin. Chitinases have been isolated from the stomachs of mammals, including humans. Chitinase activity can also be detected in human blood and possibly cartilage. As in plant chitinases this may be related to pathogen resistance. == Clinical significance ==

Chitinases production in the human body (known as "human chitinases") may be in response to allergies, and asthma has been linked to enhanced chitinase expression levels. Human chitinases may explain the link between some of the most common allergies (dust mites, 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 in humans a link between salicylic acid and allergies is only hypothetical. == Regulation in fungi ==

Regulation varies from species to species, and within an organism, chitinases with different physiological functions would be under different regulation mechanisms. For example, chitinases that are involved in maintenance, such as remodeling the cell wall, are constitutively expressed. However, chitinases that have specialized functions, such as degrading exogenous chitin or participating in cell division, need spatio-temporal regulation of the chitinase activity. 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 network (MEN), 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. == Presence in food ==

Chitinases occur naturally in many common foods. Phaseolus vulgaris, == Applications ==

Chitinases have a wealth of applications, some of which have already been realized by industry. This includes bio-conversion of chitin to useful products such as fertilizer, the production of non-allergenic, non-toxic, biocompatible, and biodegradable materials (contact lenses, artificial skin and sutures with these qualities are already being produced) and enhancement of insecticides and fungicides. Phaseolus vulgaris chitinase - bean chitinase, BCH - has been transgenically inserted as a pest deterrent into entirely unrelated crops. 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. == See also ==