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From Proteopedia

Revision as of 05:12, 30 October 2010

Lysozyme - Hen Egg White (HEW)

Lysozyme is an enzyme that breaks down cell walls by hydrolyzing certain glycosidic linkages in the peptidoglycan of cell walls. It is found in the cells and secretions of various vertebrates, and likely functions as an bacteria-killing or -disposal agent. The lysozyme found in hen egg white has been investigated more thoroughly than other species of lysozyme, and so is better understood then most enzymes.^[1] The PDB code of HEW lysozyme shown on this page is 3IJU and the assigned EC number for lysozyme is EC 3.2.1.17.

History

The enzyme Lysozoyme was first discovered and named in 1922 by Alexander Fleming. Fleming contaminated petri plates containing gram-positive bacteria with nasal mucous. After this contamination, he found that the bacterial cells on the petri plates had been lysed. He continued to investigate the cause of the cell lysis, and discovered lysozyme.^[2] He also discovered that lysozyme only works on gram-positive cells, and not on gram-negative cells. Gram-negative cells have an outer cell membrane containing lipopolysaccharides, which cannot be digested by lysozyme.^[3] Gram-positive cells, however, do not have this outer membrane, and so can be lysed by lysozyme.

The structure of HEW Lysozyme was investigated and found out in 1965 by David Phillips, making it the first enzyme to have its structure determined. Phillips initially elucidated the structure through X-Ray crystallography and then continued his investigation of substrate binding by building models of the enzyme.It was through this larger-scale model building that Phillips was able to identify the catalytic site of lysozyme.^[4]

Structure

Basics

HEW Lysozyme is a small enzyme, weighing 14.3 kD and containing only 129 amino acid residues. From his determination of the structure, Phillips found that lysozyme had an ellipsoidal shape and a prominent cleft which acted as the sustrate-enzyme binding site. This can be seen best when looking at a surface view of the protein. The two amino acids that most directly interact with the substrate when cutting glycosidic bonds are (Gln is blue and Asp is purple).

Secondary Structures

The of HEW lysozyme are split into two groups. First, there are seven alpha helices (in green), which are in random coils. Second there is one beta sheet (in blue), which contains three antiparallel strands.

Intermolecular Forces

In general, there are many intermolecular forces within the structure of lysozyme, two of these being disulfide bonds and hydrogen bonds. HEW lysozyme has eight total disulfide bonds- four are , and the other four are . HEW lysozyme has numerous hydrogen bonds between its , and even more between its . These bonds help to stabilize the enzyme and hold it together in the correct orientation.

Catalytic Reaction

Lysozyme catalyzes a reaction between

Mechanism

Current Uses

References

1. ↑ Voet, D., Voet, J., Pratt, C.(2008) Fundamentals of Biochemistry: Life at the Molecular Level, 3rd edition. John Wiley and Sons, Inc.
2. ↑ copyright 2006-2008. http://lysozyme.co.uk/
3. ↑ http://en.wikipedia.org/wiki/Gram-negative_bacteria
4. ↑ Voet, D., Voet, J., Pratt, C.(2008) Fundamentals of Biochemistry: Life at the Molecular Level, 3rd edition. John Wiley and Sons, Inc.