Hen Egg-White (HEW) Lysozyme

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Hen egg-white lysozyme, 1HEW (scroll down for interactive figure)
Hen egg-white lysozyme, 1HEW (scroll down for interactive figure)

Lysozyme - also known as muramidase, or glycoside hydrolase - is a powerful enzyme of biological significance found in abundance in tears, saliva, and human milk. In humans, it is encoded in the LYZ gene. Although it is responsible for the initial digestion of starches in the mouth, it is most widely identified as a non-specific defense in gram positive bacteria and in many species of fungi. Due to its antibacterial effects, it is a strong component of the innate immune system, and is an important part of an infant's diet to ward off diarrheal diseases. Since it is a small, easily available, and highly stable protein containing only 129 amino acid residues, it has been subject to extensive research regarding its function and structure. Hen Egg White (HEW) Lysozyme is shown below.

Introduction

Lysozyme is an enzyme known for its unique ability to degrade the polysaccharide architecture of many kinds of cell walls, normally for the purpose of protection against bacterial infection[1]. Its effects were first noticed by Laschtschenko in 1909. It was officially characterized and termed “lysozyme” by Alexander Fleming, the same person credited for the accidental discovery of penicillin. The characterization of lysozyme in 1922 by Alexander Fleming was providential in that the undertaken experiment related to the discovery of lysozyme was not geared toward any knowledge of such a protein as lysozyme [2]. During the unrelated experiment, nasal drippings were inadvertently introduced to a petri dish containing a bacterial culture, which culture consequently exhibited the results of an as yet unknown enzymatic reaction. The observation of this unknown reaction led to further research on the components of this reaction as well as to the corresponding identification of the newfound "lysozyme." Fleming's discovery was complemented by David C. Phillips' 1965 description of the three-dimensional structure of lysozyme via a 200 pm resolution model obtained from X-ray crystallography [3]. Phillips' work was especially groundbreaking since Phillips had managed to successfully elucidate the structure of an enzyme via X-ray crystallography - a feat that had never before been accomplished[4]. Phillips' research also led to the first sufficiently described enzymatic mechanism of catalytic action [5]. Thus, Phillips' elucidation of the function of lysozyme led Phillips to reach a more general conclusion on the diversity of enzymatic chemical action in relation to enzymatic structure. Clearly, the findings of Phillips as well as the more general historical development of the understanding of the structure and function of lysozyme have been paramount to the more general realm of enzyme chemistry.
See also

Function

Lysozyme Cleavage Site
Lysozyme Cleavage Site[6]

Lysozyme is known for damaging bacterial cell walls by catalyzing the hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid (NAM) and N-acetyl-D-glucosamine (NAG) residues in peptidoglycan, and between N-acetyl-D-glucosamine residues in chitodextrins. In this way, lysozyme is efficient in lysing the cell walls of both bacteria and fungi. The location of cleavage for lysozyme on this architectural theme is the β(1-4) glycosidic linkage connecting the C1 carbon of NAM to the C4 carbon of NAG.

The particular substrate of preference for this cleavage type is a (NAG-NAM)₃ hexasaccharide, within which substrate occurs the cleaving target glycosidic bond, NAM₄-β-O-NAG₅. The individual hexasaccharide binding units are designated A-F, with NAM₄-β-O-NAG₅ glycosidic bond cleavage preference corresponding to a D-E unit glycosidic bond cleavage preference.


Hen egg white lysozyme (PDB code 1hew)

See Also

References

  1. Lysozyme. 2010. Citizendium.org. http://en.citizendium.org/wiki/Lysozyme
  2. Lysozyme. 2008. Lysozyme.co.uk. http://lysozyme.co.uk/
  3. Lysozyme, 2008. Lysozyme.co.uk. http://lysozyme.co.uk/
  4. Bugg, T. 1997. An Introduction to Enzyme and Coenzyme Chemistry. Blackwell Science Ltd., Oxford
  5. 1967. Proc R Soc Lond B Bio 167 (1009): 389–401.
  6. Image from: http://www.vuw.ac.nz/staff/paul_teesdale-spittle/essentials/chapter-6/proteins/lysozyme.htm
  7. http://mcdb-webarchive.mcdb.ucsb.edu/sears/biochemistry/tw-enz/lysozyme/HEWL/lysozyme-overview.htm
  8. http://www.worthington-biochem.com/ly/default.html
  9. Image from: http://www.google.com/imgres?imgurl=http://www.vuw.ac.nz/staff/paul_teesdale-spittle/essentials/chapter-6/pics-and-strucs/lysozyme-mech.gif&imgrefurl=http://www.vuw.ac.nz/staff/paul_teesdale-spittle/essentials/chapter-6/proteins/lysozyme.htm&usg=__ormapG4XKg-tR5GrMSOdSMTV4vE=&h=603&w=801&sz=7&hl=en&start=17&zoom=1&tbnid=nvr9gvFrUILDkM:&tbnh=143&tbnw=189&prev=/images%3Fq%3DThe%2Blysozyme%2Breaction%2Bmechanism%26um%3D1%26hl%3Den%26sa%3DN%26biw%3D1280%26bih%3D647%26tbs%3Disch:10%2C304&um=1&itbs=1&iact=hc&vpx=521&vpy=349&dur=448&hovh=191&hovw=254&tx=140&ty=48&ei=JQ_LTPKzLIjCsAPkzt2KDg&oei=IA_LTP74OsG78gapm-GFAQ&esq=2&page=2&ndsp=18&ved=1t:429,r:2,s:17&biw=1280&bih=647
  10. Lysozyme, 2008. Lysozyme.co.uk. http://lysozyme.co.uk/
  11. Pratt, C.W., Voet, D., Voet, J.G. Fundamentals of Biochemistry - Life at the Molecular Level - Third Edition. Voet, Voet and Pratt, 2008.
  12. Johnson LN, Phillips DC. Structure of some crystalline lysozyme-inhibitor complexes determined by X-ray analysis at 6 Angstrom resolution. Nature. 1965 May 22;206(986):761-3. PMID:5840126
  13. Phillips, D. C. The hen egg white lysozyme molecule. Proc. Natl Acad. Sci. USA 57, 483-495 (1967)
  14. coordinates of the model kindly provided by Louise Johnson
  15. Vocadlo DJ, Davies GJ, Laine R, Withers SG. Catalysis by hen egg-white lysozyme proceeds via a covalent intermediate. Nature. 2001 Aug 23;412(6849):835-8. PMID:11518970 doi:10.1038/35090602

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