Sandbox 36

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Please do NOT make changes to this Sandbox. Sandboxes 30-60 are reserved for use by Biochemistry 410 & 412 at Messiah College taught by Dr. Hannah Tims during Fall 2012 and Spring 2013.


Contents

Lysozyme

Overview

Lysozyme is an enzyme that inhibits the growth of bacteria through lyses of the cell walls. It can be found in salvia, tears, other bodily secretions. Lysozyme is also present in high concentrations in hen egg whites. Lysozyme small size and high stability makes it ideal for protein structure and function research. Furthermore, the enzyme is easy to purify from egg whites and easy to crystallize, unlike most proteins.

Structure

The lysozyme used to analyze structural features was isolated from the eggs of the chicken Gallus gallus. Alternatives names for this lysozyme include 1,4-beta-N-acetylmuramidase C, Allergen Gal d IV, Allergen=Gal d 4. The European Commission number, or EC number, is 3.2.1.17. The sequence consists of 147 amino acids with a molecular weight of 16kD.

Secondary Structure

Gallus gallus egg white lysozyme has an alpha+beta fold, consisting of seven alpha helices and a three-stranded antiparallel beta sheet. There is also and a large amount of random coil and beta turns. The enzyme is approximately ellipsoidal in shape, with a large cleft in one side forming the active site. The openness of the secondary representation does not allow cleft identification. Click to visualize the cartoon portrayal of the enzyme with alpha helices and beta sheets highlighted. The alpha helix are highlighted in green and the beta sheets in clue. Click for the rainbow color ordered cartoon chain from N-C terminal.

Egg White Lysozyme

Drag the structure with the mouse to rotate

Function

Lysozyme’s main function is to protect from infection. The enzyme is a general non-specific organism defense effective against gram positive bacterial cells. Lysozyme degrades the polysaccharides found in cells walls by catalyzing the hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins[1]. X-ray crystallography has shown that the binding of lysozyme and the substrates slightly deforms both structures. The binding first distorts the fourth hexose in the chain to the half chair conformation [2]. This imposes a strain on the C-O bond on the ring-4 side of the oxygen bridge between rings 4 and 5[3]. The polysaccharide is broken at this point and a molecule of water is inserted between the two hexoses. The reaction mechanism is shown below.

Image:Lys.gif

History

Lysozyme was first discovered by Alexander Fleming during his research for medical antibiotics. When searching for any sort of bacterial inhibitor, he added a drop of mucus to a live culture. To Fleming’s surprise, it successfully killed the bacteria. The phenomena was carefully analyzed and it was proved that lysozyme was the main active enzyme. Fleming had discovered one of the human body’s natural defenses against infection. Lysozyme could not successfully be used as an antibiotic however, because its large size inhibits transportation through cells[4]. The enzyme has been used in protein structure and function research because of its unique properties.

As mentioned earlier lysosyme can be purified from hen egg-whites and crystallized quite simply. This has made the it the best object for X-Ray analysis for many years. The X-Ray beam diffraction of lysozyme crystals also has a extremely high resolution, reaching 0.94 Angstroms. Lysozyme was the first enzyme to ever have its structure solved. In 1965 David Chilton Phillips successfully solved the structure through X-Ray analysis with 2 angstrom resolution[5]. Today lysozyme is still being used in research and is also commercially valuable enzyme used for many purposes, including the treatment of ulcers and infections, and as a food and drug preservative.


References

  1. ↑ Lysozyme. (2008). Retrieved from http://lysozyme.co.uk/
  2. ↑ Voet, D, G., J, & W., C. (2008). Fundamentals of biochemistry: life at the molecular level. John Wiley & Sons Inc
  3. ↑ http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/Enzymes.html#lysozyme
  4. ↑ Goodsell, D. (2000, September). Lysozyme. Retrieved from http://www.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/pdb9_1.html
  5. ↑ Lysozyme. (2008). Retrieved from http://lysozyme.co.uk/
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