07 Lysozyme - Lysozyme Lysozyme is part of the innate...

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Lysozyme Lysozyme is part of the innate immune system of the human body. It is a protein found in many body secretions – tears, saliva, and the mucus protecting the gut and bronchi. It is an enzyme which breaks down bacterial cell wall polysaccharides, destroying the cell wall and killing the bacterium. Lysozyme is small – only 129 amino acids, with a molecular weight of 14.6kD. It is ellipsoid in shape with dimensions of 3 x 3 x 4.5 nm. Its main feature is a cleft running across one face of the molecule. This cleft constitutes the substrate binding site, and the actual catalytic site is contained within it. Lysozyme brings about its action without using any form of co-factor. Its catalytic action is a property of the protein molecule itself. The aim of this lecture is to explain in full molecular detail how the catalytic action of lysozyme works, and in doing so give an illustrative example of enzyme catalysis at the molecular level.
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Lysozyme’s Substrate The cell wall polysaccharide which lysozyme cleaves consists of long strands of hexose sugar molecules, linked together by β 1-4 glycoside bonds. These bonds are typical of structural carbohydrates (they are also found in cellulose and chitin). They allow the polysaccharide to form straight chains. They are usually very resistant to breaking. In the bacterial cell wall polysaccharide the hexose sugars are alternate molecules of N-acetyl glucosamine and N-acetyl muraminic acid, but the enzyme will also hydrolyse chitin – the structural component of fungal cell walls and insect exoskeletons. This is made up of N-acetyl glucosamine only. The lysozyme active site cleft can accommodate six sugar units of the polysaccharide.
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N-Acetyl Glucosamine and N-acetyl muraminic acid
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The Cleavage Reaction Lysozyme cleaves its substrate between C4 of NAG and C1 of NAMA. The reaction is a hydrolysis. A C-O bond is cleaved,
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This note was uploaded on 02/25/2012 for the course CHEM 1341 taught by Professor Compton during the Fall '08 term at Texas State.

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07 Lysozyme - Lysozyme Lysozyme is part of the innate...

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