Chitinases (EC 3.2.1.14, chitodextrinase, 1,4-β-poly-N-acetylglucosaminidase, poly-β-glucosaminidase, β-1,4-poly-N-acetyl glucosamidinase, poly
D-glucosaminide)">,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
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s that break down
glycosidic bond
A glycosidic bond or glycosidic linkage is a type of covalent bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.
A glycosidic bond is formed between the hemiacetal or hemiketal group ...
s in
chitin.
They catalyse the following reaction:
: Random endo-hydrolysis of ''N''-acetyl-β-
D-glucosaminide (1→4)-β-linkages in chitin and chitodextrins
As chitin is a component of the
cell walls of
fungi
A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
and
exoskeletal elements of some animals (including
mollusk
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...
s and
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s), chitinases are generally found in organisms that either need to reshape their own chitin
or dissolve and digest the chitin of fungi or animals.
Species distribution
Chitinivorous organisms include many bacteria
(
Aeromonads, ''
Bacillus
''Bacillus'' (Latin "stick") is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum '' Bacillota'', with 266 named species. The term is also used to describe the shape (rod) of other so-shaped bacteria; and the plural ''Bacill ...
'', ''
Vibrio
''Vibrio'' is a genus of Gram-negative bacteria, possessing a curved-rod (comma) shape, several species of which can cause foodborne infection, usually associated with eating undercooked seafood. Being highly salt tolerant and unable to survive ...
'',
among others), which may be
pathogenic or detritivorous. They attack living
arthropod
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s,
zooplankton
Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
or fungi or they may degrade the remains of these organisms.
Fungi, such as ''
Coccidioides
''Coccidioides'' is a genus of dimorphic ascomycetes in the family Onygenaceae. Member species are the cause of coccidioidomycosis, also known as San Joaquin Valley fever, an infectious fungal disease largely confined to the Western Hemisphere ...
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
Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley p ...
seed chitinase: , . Barley seeds are found to produce
clone 10 in Ignatius et al 1994(a). They find clone 10, a
Class I chitinase
Chitinases (EC 3.2.1.14, chitodextrinase, 1,4-β-poly-N-acetylglucosaminidase, poly-β-glucosaminidase, β-1,4-poly-N-acetyl glucosamidinase, poly ,4-(N-acetyl-β-D-glucosaminide)glycanohydrolase, (1→4)-2-acetamido-2-deoxy-β-D-glucan glycano ...
, in the seed
aleurone Aleurone (from Greek ''aleuron'', flour) is a protein found in protein granules of maturing seeds and tubers. The term also describes one of the two major cell types of the endosperm, the aleurone layer. The aleurone layer is the outermost layer of ...
during development.
Leaves produce several
isozyme In biochemistry, isozymes (also known as isoenzymes or more generally as multiple forms of enzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction. Isozymes usually have different kinetic parameters (e.g. dif ...
s (as well as several of
β-1,3-glucanase
Glucanases are enzymes that break down large polysaccharides via hydrolysis. The product of the hydrolysis reaction is called a glucan, a linear polysaccharide made of up to 1200 glucose monomers, held together with glycosidic bonds. Glucans are ab ...
). Ignatius et al 1994(b) find these in the leaves, induced by
powdery mildew
Powdery mildew is a fungal disease that affects a wide range of plants. Powdery mildew diseases are caused by many different species of ascomycete fungi in the order Erysiphales. Powdery mildew is one of the easier plant diseases to identify, a ...
.
Ignatius et al also find these (seed and leaf isozymes) to differ from each other.
[ .] Some of these are
pathogenesis related (PR) proteins Pathogenesis-related (PR) proteins are proteins produced in plants in the event of a pathogen attack. They are induced as part of systemic acquired resistance. Infections activate genes that produce PR proteins. Some of these proteins are antimicro ...
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
In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relat ...
products. The multimer products includes di-acetylchitobiose, chitotriose, and chitotetraose, with the dimer being the predominant product.
![Endochitinase](https://upload.wikimedia.org/wikipedia/commons/2/29/Endochitinase.png)
#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
oligosaccharide
An oligosaccharide (/ˌɑlɪgoʊˈsækəˌɹaɪd/; from the Greek ὀλίγος ''olígos'', "a few", and σάκχαρ ''sácchar'', "sugar") is a saccharide polymer containing a small number (typically two to ten) of monosaccharides (simple sug ...
s 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).
![Exochitinase](https://upload.wikimedia.org/wikipedia/commons/d/d2/Exochitinase.png)
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.
Therefore, the chitinases were grouped into three
families
Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...
:
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.
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
inducer
In molecular biology, an inducer is a molecule that regulates gene expression. An inducer functions in two ways; namely:
*By disabling repressors. The gene is expressed because an inducer binds to the repressor. The binding of the inducer to the r ...
s.
chitinases had a cysteine-rich ''N''-terminal, leucine- or valine-rich signal peptide, and
vacuolar
A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...
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
In molecular biology, binding domain is a protein domain which binds to a specific atom or molecule, such as calcium or DNA. A protein domain is a part of a protein sequence and a tertiary structure that can change or evolve, function, and liv ...
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.
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
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...
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
Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermat ...
, and
asthma
Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...
has been linked to enhanced chitinase expression levels.
Human chitinases may explain the link between some of the most common allergies (
dust mite
House dust mites (HDM, or simply dust mites) are various species of acariform mites belonging to the family Pyroglyphidae that are found in association with dust in dwellings. They are known for causing allergies.
Biology
Species
The curren ...
s, mold spores—both of which contain chitin) and
worm
Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always).
Worms vary in size from microscopic to over in length for marine polychaete wo ...
(
helminth) infections, as part of one version of the
hygiene hypothesis
In medicine, the hygiene hypothesis states that early childhood exposure to particular microorganisms (such as the gut flora and helminth parasites) protects against allergic diseases by contributing to the development of the immune system. In pa ...
(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 diseas
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
Spatiotemporal gene expression, spatio-temporal regulation of the chitinase activity.
The regulation of an endochitinase in ''
Trichoderma
''Trichoderma'' is a genus of fungi in the family Hypocreaceae that is present in all soils, where they are the most prevalent culturable fungi. Many species in this genus can be characterized as opportunistic avirulent plant symbionts. This ref ...
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
''Saccharomyces cerevisiae'' () (brewer's yeast or baker's yeast) is a species of yeast (single-celled fungus microorganisms). The species has been instrumental in winemaking, baking, and brewing since ancient times. It is believed to have b ...
'' and the regulation of ScCts1p (''S. cerevisiae'' chitinase 1), one of the chitinases involved in cell separation after
cytokinesis
Cytokinesis () is the part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the late stages of nuclear division in mitosis and mei ...
by degrading the chitin of the
primary septum. As these types of chitinases are important in
cell division
Cell division is the process by which a parent cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukaryotes, there ar ...
, 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. ''
Phaseoleus vulgaris'',
bananas, chestnuts, kiwifruit, avocados, papaya, and tomatoes, for example, all contain significant levels of chitinase, as defense against fungal and invertebrate attack. Stress, or environmental signals like
ethylene gas, may stimulate increased production of chitinase.
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.
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
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
, the production of non-allergenic, non-toxic,
biocompatible
Biocompatibility is related to the behavior of biomaterials in various contexts. The term refers to the ability of a material to perform with an appropriate host response in a specific situation. The ambiguity of the term reflects the ongoing de ...
, and
biodegradable materials (
contact lenses
Contact lenses, or simply contacts, are thin lenses placed directly on the surface of the eyes. Contact lenses are ocular prosthetic devices used by over 150 million people worldwide, and they can be worn to correct vision or for cosmeti ...
,
artificial skin Artificial skin is a collagen scaffold that induces regeneration of skin in mammals such as humans. The term was used in the late 1970s and early 1980s to describe a new treatment for massive burns. It was later discovered that treatment of deep ski ...
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
Rhinosinusitis is a simultaneous infection of the nasal mucosa (rhinitis) and an infection of the mucosa of the paranasal sinuses ( sinusitis). A distinction is made between acute rhinosinusitis and chronic rhinosinusitis.
Background
Because sin ...
, as an anti-fungal remedy, an anti-tumor drug and as a general ingredient to be used in
protein engineering.
See also
*
Ligninase Lignin-modifying enzymes (LMEs) are various types of enzymes produced by fungi and bacteria that catalyze the breakdown of lignin, a biopolymer commonly found in the cell walls of plants. The terms ligninases and lignases are older names for the sam ...
References
External links
*
The X-ray structure of a chitinase from the pathogenic fungus Coccidioides immitis
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EC 3.2.1
Enzymes