There are many types of Chitinases from those found in bacteria to fungal, plant, and to those found in humans. Chitinases are usually found in organisms that digest the chitin of fungi or animals or organisms that need to reshape their own chitin. You will find these in the cell walls of certain fungi and the exoskeleton of some animals, and it is an important element due to its function. It is also thought that some chitinases that have been produced in the human body may be related to certain types of allergies such as dust mites. Asthma has also been linked to enhanced chitinase expression levels in the human body, which was proved by a study conducted by scientists in this field.
Chitinases are a catalytic mechanism, and each class shows different reaction mechanisms. Due to the different classes, there are multiple mechanisms, including inverting and retaining. It depends on what reaction is being carried out, to the type of mechanism that you will find in chitinase. For example, plant chitinases use two different types of hydrolytic mechanisms, but they are all catalytic mechanisms.
Chitinase can be found in human blood and in some cases, cartilage. Digesting chitins is not an easy task, which is why animals require lengthy fermentations and bacterial symbionts to be able to do this. Chitin is similar to cellulose and is a bipolymer which is quite resistant to degradation, which is why it is not typically digested by animals other than a few species of fish. Even though this is the case, some animals have been found chitins when they have isolated certain parts of the stomach in animals, and this has included humans. Essentially, chitinase are enzymes that break down glycosidic bonds in chitin, which is why it is only found in certain animals that have chitin in their body.
As there are different types of chitinase, there are various structures that can be found when they are studied. However, most commonly they are found to have a crystal structure such as that in GH18 found in certain fungi, plants, and animals. This has shown researchers that even though the crystal structure seems to be constant between chitinase and so does the catalytic mechanism, there does seem to be rather large discrepancies between the binding cleft. There are three distinct domains in chitinase, and these are the N-terminal chitin-binding domain, the TIM barrel catalytic domain and the A + B insertion domain. Each of these combines to make up the structure of at least one of the GH18 chitinases.
One study that was completed has stated that Vibrio Harveyi chitinase is a GH18 enzyme that has three distinct domains. The chitin-binding domain from Vibrio Harveyi is crucial for when it comes to chitin-chitinase interaction. The catalytic domain of this works together with the chitin-binding domain to get the polymeric substrate into the binding cleft. This research has seemed to confirm the role of the chitin-binding domain of GH18 chitinase in chitin-chitinase interactions.