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Papain digests a large variety of proteins, with a very broad specificity. Its <scene name='Sandbox_34/9pap_active_site/1'>active site</scene>consists of the residues cysteine-25, histidine-159, and asparagine-175. It cleaves the peptide bonds of basic amino acids, leucine and glycine by nucleophilic attack with its sulfhydryl group on cysteine-25 <ref>http://www.ebi.ac.uk/QuickGO/GTerm?id=GO:0004197</ref>. It also hydrolyzes esters and amides. It prefers amino acids that bear large hydrophobic side chains at the P2 position, and will not accept valine at the P1' position. <ref name="UniProt" /> | Papain digests a large variety of proteins, with a very broad specificity. Its <scene name='Sandbox_34/9pap_active_site/1'>active site</scene>consists of the residues cysteine-25, histidine-159, and asparagine-175. It cleaves the peptide bonds of basic amino acids, leucine and glycine by nucleophilic attack with its sulfhydryl group on cysteine-25 <ref>http://www.ebi.ac.uk/QuickGO/GTerm?id=GO:0004197</ref>. It also hydrolyzes esters and amides. It prefers amino acids that bear large hydrophobic side chains at the P2 position, and will not accept valine at the P1' position. <ref name="UniProt" /> | ||
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| + | == Catalytic Mechanism == | ||
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| + | [[Image:PapainMechanism.gif|200px|left|thumb]] | ||
== Inhibitors == | == Inhibitors == | ||
Revision as of 00:45, 14 November 2011
| 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 |
Papain
Introduction
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Papain is a cysteine protease, also known as papaya proteinase I, from the peptidase C1 family with E.C. 3.4.22.2. It functions as a hydrolase, endopeptidase, and thiol protease.[1] Its optimal activity values for pH lie between 6.0 and 7.0, and 65 °C as its optimal temperature for activity. Its pI values are 8.75 and 9.55. Papain is best visualized at a wavelength of 278 nm. [2] Naturally found in the latex of the papaya fruit, one of the most common uses of papain is as a meat tenderizer because of its ability to hydrolyze esters and amides.[3] Another common use is as a digestive aid. Papaya is commonly referenced as a preferred fruit for those suffering from gastroesophageal reflux disease due to its ability to help the the stomach with digestion of complex proteins.
History
Papain's enzymatic use was first discovered in 1873 by G.C. Roy who published his results in the Calcutta Medical Journal in the article, "The Solvent Action of Papaya Juice on Nitrogenous Articles of Food."[4] In 1879, papain was named officially by Wurtz and Bouchut, who managed to partially purify the product from the sap of papaya.[4]. It wasn't until the mid-twentieth century that the complete purification and isolation of papain was achieved. In 1968, Drenth et al. determined the structure of papain by x-ray crystallography, making it the second enzyme whose structure was successfully determined by x-ray crystallography. Additionally, papain was the first cysteine protease to have its structure identified. [4] In 1984, Kamphuis et al. determined the geometry of the active site, and the three-dimensional structure was visualized to a 1.65 Angstrom solution.[5] Today, studies continue on the stability of papain, involving changes in environmental conditions, in addition to testing of inhibitors such as phenylmethanesulfonylfluoride (PMSF), TLCK, TPCK, aplh2-macroglobulin, heavy metals, AEBSF, antipain, cystatin, E-64, leupeptin, sulfhydryl binding agents, carbonyl reagents, and alkylating agents.[4]
Structure
Papain is a relatively simple enzyme. It consists of only one chain of 212 residues with three disulfide bonds, illustrated in yellow.[5] A modified cysteine residue with a sulhydryl group, , is necessary for the activity of the enzyme.[6] In 9PAP, the sulfhydryl group has been oxidized. Papain contains many illustrated in magenta.
Ligands
Papain binds many methanol molecules via hydrogen bonding.
Specificity
Papain digests a large variety of proteins, with a very broad specificity. Its consists of the residues cysteine-25, histidine-159, and asparagine-175. It cleaves the peptide bonds of basic amino acids, leucine and glycine by nucleophilic attack with its sulfhydryl group on cysteine-25 [7]. It also hydrolyzes esters and amides. It prefers amino acids that bear large hydrophobic side chains at the P2 position, and will not accept valine at the P1' position. [1]
Catalytic Mechanism
Inhibitors
There are many inhibitors for papain because of its broad specificity. [8]
References
- ↑ 1.0 1.1 http://www.uniprot.org/uniprot/P00784
- ↑ http://www.sigmaaldrich.com/life-science/metabolomics/enzyme-explorer/analytical-enzymes/papain.html
- ↑ IUBMB Enzyme Nomenclature: www.chem.qmul.ac.uk/iubmb/enzyme/EC3/4/22/2.html
- ↑ 4.0 4.1 4.2 4.3 http://www.worthington-biochem.com/pap/default.html
- ↑ 5.0 5.1 Kamphuis IG, Kalk KH, Swarte MB, Drenth J. Structure of papain refined at 1.65 A resolution. J Mol Biol. 1984 Oct 25;179(2):233-56. PMID:6502713
- ↑ http://www.sigmaaldrich.com/life-science/metabolomics/enzyme-explorer/analytical-enzymes/papain.html
- ↑ http://www.ebi.ac.uk/QuickGO/GTerm?id=GO:0004197
- ↑ Tsuge H, Nishimura T, Tada Y, Asao T, Turk D, Turk V, Katunuma N. Inhibition mechanism of cathepsin L-specific inhibitors based on the crystal structure of papain-CLIK148 complex. Biochem Biophys Res Commun. 1999 Dec 20;266(2):411-6. PMID:10600517 doi:10.1006/bbrc.1999.1830
