Sandbox 32: Difference between revisions

=='''Catalytic Mechanism'''==

As a sulfhydryl protease, Papain has a catalytic site with three important residues --Cysteine-25, Histidine-159,and Asparganine176 (4). The catalytic site is located in the <scene name='Sandbox_32/Binding_cleft/2'>binding cleft</scene> between the L and R domains of the protein  The <scene name='Sandbox_32/Catalytic_site/1'>catalytic site</scene> centers around Cysteine-25 as it is a sulfhydryl protease. Sulfur on the cysteine will nucelophilically attack its substrate. Histidine acts to deprotonate sulfur (Cys-25), allowing it to be negatively charged. Once sulfur attacks the peptide,the tetrahedral intermediate is stabilized by a proposed oxyanion hole, specifically by asparganine (Asn-176) (1). The charged imidazolium ion of papain will in turn protanate  the nitrogen in the peptide bond, releasing the C-terminal part of the peptide (5). Water enters the active site and ultimately regenerates the enzyme and allowing for the release of the N-terminal portion of the cleaved peptide.