- The lysozyme enzyme is added to distort the NAM molecule to convert the strand from chair conformation to half-chair conformation. This half-chair confirmation increases the strength of the bond and distorts the residue making it easier to break the glycosidic bond.
- Within the active site, Glu-35 transfers its H to the O of glycosidic linkage (general acid-base catalysis), thus breaking the glycosidic bond and producing an oxocarbonium ion (positive).
- Asp-52 contains a negatively charged carboxyl group that reacts with oxocarbonium ions and stabilizes it (electrostatic catalysis).
- Water molecules enter as the 2nd substrate and OH-NAG is excreted as the first product.
- The oxocarbonium ion attaches itself to the OH-ion of the water molecule and separates Asp-52. The H + ion of the remaining water returns to its previous state with Glu-35 (general acid-base catalysis).
Function of lysozyme enzyme:
The active site of the enzyme binds to the hexameric unit of the substrate and deforms the fourth sugar (D residue) into a half-chair confirmation.
There are two main functions of lysozyme enzymes
- Breaks B1 → 4 glycosidic link between C1 of N-acetylmuramic acid (NAM) and C4 of N-acetylglucosamine (NAG) (hydrolytic cleavage). This B1 → 4 glycosidic link is found in the cell wall of various microorganisms, especially bacteria. This means that the lysozyme enzyme can destroy bacteria by breaking down the cell wall.
- By hydrolytic cleavage, is able to destroy fungal cell wall which is composed of chitin.
The role of lysozyme:
- The lysozyme enzyme acts as part of the immune system. Excessive depletion of this enzyme can lead to bronchopulmonary dysplasia in children .
- Pigs that suffer from diarrhea caused by E. coli can be cured of this disease if they are fed human lysozyme milk. The concentration of lysozyme in human milk is up to 3000 times that of lysozyme in domestic milk. Therefore, the lysozyme of human milk is more active than the white part of chicken egg.
- Lysozyme develops resistance against Gram-positive bacteria. Mainly Bacillus and Streptococcus.
- Many times cancer cells produce excessive amounts of lysozyme. Excessive lysozyme then causes poisoning.
- Plays an important role in preventing bacterial infections.
- Plays a role in the treatment of primary malignancy.
- High levels of lysozyme in the blood cause nephrosis (kidney failure) and lower potassium levels in the blood.
- It is used as an indicator of pathological disease activity.
- Lysozyme enzymes are also used in various biomedical fields where lysozyme helps in the production of different types of functional radicals, causes bacterial lysis and so on.
Lysozyme is an elliptical globular enzyme composed of a single polypeptide chain of 129 amino acids. The chain consists of four disulfide bridges with 5 helical segments and 3 parallel beta strands. Glu-35 and Asp-51 form catalytic diodes. Glu-35 is in protonated form and Asp-51 is in unprotected form. Together they take part in acid base catalysis.
Characteristics of lysozyme enzyme:
- Thermally stable.
- Melting point can be up to 72 degree Celcius.
- pH 5.0 (however, the lysozyme of the white part of the chicken can survive up to pH 9.0).
- Iso-electric point 11.35
Lysozyme is found in tears, saliva, human milk, mucus, cytoplasmic grains of macrophages, egg whites (chicken), leukocytes, kidney tissue, etc. There is a type of lysozyme called C-type lysozyme. Their structure and sequence are closely related to alpha-lactalbumin. This C-type lysozyme is encoded by LYZ Gin. The white part of the chicken egg contains lysozyme and they are thermally stable, the melting point of this lysozyme is up to 72 degrees.
History of lysozyme enzyme:
Laschtschenko first observed the antibacterial properties of chicken egg whites in 1909. Alexander Fleming explained the antibacterial activity of the nasal mucosa in 1922. Fleming was the first to use the term lysozyme. Fleming showed that different types of secretions contain a type of enzymatic component that is capable of bacterial lysis.
Edward Abraham was later able to crystallize lysozyme in 1936. In 1975, David Chilton Philips explained the three-dimensional arrangement of the white part of a chicken egg. Lysozyme is the first enzyme to contain all 20 amino acids in a sequence.
Imidazole derivatives combine with some residues outside or inside the active nucleus to form a charge-transfer complex to compete with lysozyme.