Sandbox 42

== Hen Egg-white Lysozyme Overview ==

The primary catalytic action of the enzyme hen egg-white lysozyme is to hydrolyze β(1→4) glycosidic linkages found in bacterial cell walls.<ref>http://lysozyme.co.uk/</ref> More specifically, lysozyme hydrolyzes the linkages from ''N''-acetylmuramic acid to ''N''-acetylglucosamine which occur in peptidoglycans of the cell wall. The small 14.3 kD Hen egg-white lysozyme is one of the most widely studied lysozymes.<ref>Voet, Voet, and Pratt. Fundamentals of Biochemistry. 3 ed. John Wiley & Sons: 2008.</ref>

== Secondary structure ==

Hen egg white lysozyme is formed from one polypetide chain 129 amino acids in length. Important <scene name='Sandbox_42/Secondary_structures/3'>secondary structures</scene> formed by the chain include 7 alpha helices and 1 beta sheet consisting of 3 anti-parallel strands. 4 disulfide bonds are involved in folding of the chain.

== Distribution of residue polarity ==

The <scene name='Sandbox_42/Hydrophobic-polar/1'>distribution of hydrophobic and polar residues</scene> in lysozyme is varied, with both types of residues on the surface of the enzyme. <scene name='Sandbox_42/Water/2'>Water</scene> interacts with polar residues of the enzyme both on the exterior and interior regions of the enzyme.

== Active site and Binding ==

Hen white lysozyme's substrate binding site accomodates six residue oligosaccharides. Glu 35 and Asp 52 are the enzyme's <scene name='Sandbox_42/Active_site/1'>active site residues</scene>. These residues have <scene name='Sandbox_42/Active_site_residue_contacts/1'>distinctly different microenvironments</scene> which are critical for their catalytic action. Asp 52 forms hydrogen bonds with surrounding residues including Asn46, Asp48, Ser50 and Asn59 on the anti-parallel beta-sheet and is negatively charged allowing for electrostatic stabilization of the reaction intermediate.<ref> PMID:19605465 </ref> Glu 35 conversely is surrounded by hydrophobic residues and its side chain stays protonated allowing for acid catalysis. Catalysis proceeds through the formation of a covalent intermediate.<ref>Voet, Voet, and Pratt. Fundamentals of Biochemistry. 3 ed. John Wiley & Sons: 2008.</ref> A mutation of T4 lysozyme allows for its product to stay bound to the enzyme. This mutation made it possible to isolate a <scene name='Sandbox_42/Ligand_and_lysozyme/1'>a covalent-substrate intermediate</scene> which also shows the <scene name='Sandbox_42/Distorted_ring/1'>predicted distortio</scene>n of the sugar in the 4th position of the active site.

== Comparative Structures ==

Hen egg-white lysozyme is a c-lysozymes in a family of lysozymes which also includes alpha-lactalbumins. Alpha-lactalbumins and c-lysozymes have very similar sequences and structures, including 4 conserved disulfide bonds<ref>C-type lysozyme/alpha-lactalbumin family. http://pfam.sanger.ac.uk/family/PF00062.</ref> However, <scene name='Sandbox_42/Alpha-lactalbumin/1'>alpha-actalbumins ligand with calcium</scene> and serve the different function of regulating the biosynthesis of milk lactose<ref>Alpha lactal-bumin. http://www.rcsb.org/pdb/explore/explore.do?structureId=1HFZ</ref>

== References ==

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