Lysozyme is a family of enzymes (EC 3.2.1.17) which damage bacterial cell walls by catalyzing hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins This article is about the Enzyme Commission codes For the European Commission system for coding chemicals see EC-No. It is abundant in a number of secretions, such as tears, saliva, and mucus. Secretion is the process of segregating elaborating and releasing chemicals from a cell, or a secreted Chemical substance or amount of substance Tears are the liquid product of a process of lacrimation to clean and lubricate the Eyes The word lacrimation may also be used in a medical or literary sense For the band see Saliva (band; for the village in Azerbaijan see Səliva. In vertebrates mucus is a slippery secretion produced by and covering Mucous membranes It is a viscous Colloid containing Antiseptic enzymes (such as Lysozyme is also present in cytoplasmic granules of the polymorphonuclear neutrophils (PMN). The cytoplasm is the contents of a cell that is enclosed within the Plasma membrane. Granulocytes are a category of White blood cells characterised by Large amounts of lysozyme can be found in egg whites. C-type lysozymes are closely related to alpha-lactalbumin in sequence and structure making them part of the same family. Lactalbumin alpha-, also known as LALBA, is a human Gene. α-lactalbumin is an important Whey protein in Cow 's Milk
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Physiology
Most of the bacteria affected by lysozyme are not pathogenic. In some cases, lysozyme is a primary reason these organisms do not become pathogenic. Lysozyme can act to some extent as an innate opsonin, or as an actively lytic enzyme. An opsonin is any molecule that acts as a binding Enhancer for the process of Phagocytosis, for example by coating the negatively-charged molecules on the membrane
Lysozyme serves as a non-specific innate opsonin by binding to the bacterial surface, reducing the negative charge and facilitating phagocytosis of the bacterium before opsonins from the acquired immune system arrive at the scene. An opsonin is any molecule that acts as a binding Enhancer for the process of Phagocytosis, for example by coating the negatively-charged molecules on the membrane In other words, lysozyme makes it easier for phagocytic white blood cells to engulf bacteria.
The enzyme functions by attacking peptidoglycans (found in the cells walls of bacteria, especially Gram-positive bacteria) and hydrolyzing the glycosidic bond that connects N-acetylmuramic acid with the fourth carbon atom of N-acetylglucosamine. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Not to be confused with Glycoprotein. Peptidoglycan, also known as murein, is a Polymer consisting of sugars and amino Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions N-Acetylmuramic acid, or MurNAc, is the Ether of Lactic acid and N-acetylglucosamine with a Chemical formula of C 11 N-Acetylglucosamine ( N-Acetyl-D-Glucosamine, or GlcNAc, or NAG) is a Monosaccharide derivative of Glucose. It does this by binding to the peptidoglycan molecule in the binding site within the prominent cleft between its two domains. Not to be confused with Glycoprotein. Peptidoglycan, also known as murein, is a Polymer consisting of sugars and amino This causes the substrate molecule to adopt a strained conformation similar to that of the transition state. According to Phillips-Mechanism the lysozyme binds to a hexasaccharide. The lysozyme then distorts the 4th sugar in hexasaccharide (the D ring) into a half-chair conformation. In this stressed state the glycosidic bond is easily broken.
The amino acid side chains glutamic acid 35 (Glu35) and aspartate 52 (Asp52) have been found to be critical to the activity of this enzyme. Glu35 acts as a proton donor to the glycosidic bond, cleaving the C-O bond in the substrate, whilst Asp52 acts as a nucleophile to generate a glycosyl enzyme intermediate. The glycosyl enzyme intermediate then reacts with a water molecule, to give the product of hydrolysis and leaving the enzyme unchanged.
- Further information: glycoside hydrolase
Role in disease
In some forms of hereditary amyloidosis, the cause is a mutation in the lysozyme gene, which leads to accumulations of lysozyme in several tissues. Glycoside hydrolases (also called glycosidases) catalyze the Hydrolysis of the Glycosidic linkage to generate two smaller Sugars They In Medicine, amyloidosis refers to a variety of conditions in which Amyloid Proteins are abnormally deposited in organs and/or tissues In biology mutations are changes to the Nucleotide sequence of the Genetic material of an organism History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Tissue is a cellular organizational level intermediate between cells and a complete organism [1]
Whereas the skin is a protective barrier due to its dryness and acidity, the conjunctiva (membrane covering the eye) is instead protected by secreted enzymes, mainly lysozyme and defensin. The conjunctiva is a clear membrane that covers the Sclera (white part of the Eye) and lines the inside of the Eyelids It is made of lymphoid tissue Defensins are small (15-20 residue) Cysteine -rich Cationic Proteins found in both Vertebrates and Invertebrates They are However when these protective barriers fail, conjunctivitis results. Conjunctivitis (commonly called " Pink Eye " or " Red Eye " in North America and " Madras eye " in India) is an inflammation
History
Alexander Fleming (1881-1955), the discoverer of penicillin, described lysozyme in 1922. Sir Alexander Fleming (6 August 1881 &ndash 11 March 1955 was a Scottish Biologist and Pharmacologist. Penicillin (sometimes abbreviated PCN or pen) is a group of Beta-lactam antibiotics used in the treatment of Bacterial Infections Year 1922 ( MCMXXII) was a Common year starting on Sunday of the Gregorian calendar. [2]
Its structure was described by David Chilton Phillips (1924-1999) in 1965 when he got the first 2 angstrom (200 pm) resolution image. David Chilton Phillips Baron Phillips of Ellesmere, KBE, FRS ( 7 March 1924 - 23 February 1999) is considered to be a founding An ångström or angstrom (symbol Å) (ˈɔːŋstrəm Swedish: ˈɔ̀ŋstrœm is an internationally recognized non- SI unit of length equal A picometre ( American spelling: picometer, symbol pm) is a unit of Length in the Metric system, equal to one trillionth [3][4] This work led Phillips to provide an explanation for how enzymes speed up a chemical reaction in terms of its physical structures. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins The original mechanism proposed by Phillips was more recently revised. [5]
Howard Florey (1898-1968) and Ernst B. Chain (1906-1979) also investigated lysozymes. Howard Walter Florey Baron Florey, OM, FRS, ( September 24, 1898 &ndash February 21, 1968) was an Australian Sir Ernst Boris Chain ( June 19, 1906 &ndash August 12, 1979) was a German -born British biochemist and a 1945 co-recipient Although they never made much progress in this field, they developed penicillin, which Fleming had failed to do.
References
- ^ Online 'Mendelian Inheritance in Man' (OMIM) 105200
- ^ Fleming A. The Mendelian Inheritance in Man project is a Database that catalogues all the known Diseases with a genetic component, and—when possible—links them On a remarkable bacteriolytic element found in tissues and secretions. Proc Roy Soc Ser B 1922;93:306-17
- ^ Blake CC, Koenig DF, Mair GA, North AC, Phillips DC, Sarma VR. Structure of hen egg-white lysozyme. A three-dimensional Fourier synthesis at 2 Ångstrom resolution. Nature, 206, 757-61
- ^ Johnson LN, Phillips DC. Structure of some crystalline lysozyme-inhibitor complexes determined by X-ray analysis at 6 Ångstrom resolution. Nature, 206, 761-3.
- ^ Vocadlo, D. J. ; Davies, G. J. ; Laine, R. ; Withers, S. G. Nature 2001, 412, 835.
External links
Dictionary
lysozyme
-noun
- (biochemistry) A bacteriolytic (or antibiotic) enzyme found in many animal secretions, and in egg white.
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