Sandbox 35

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<Structure load='1AKE' size='500' frame='true' align='right' caption='Adenylate Kinase' scene='Insert optional scene name here' />
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==Adenylate Kinase==
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Adenylate kinase, also known as "ADK", is an enzyme which speeds up the reaction that includes the interconversion of adenine nucleotides. The protein's flexibility allows it to bind to certain substrates known as ligands. Adenylate kinase is known for influencing cellular energy homeostasis.
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= '''Papain''' =
 
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==Introduction==
 
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[[Image:Papain_cartoon.png|200px|left|thumb|Cartoon Peak at Pepsin]]
 
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DID YOU KNOW?
 
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<scene name='Sandbox_35/Papain/1'>Papain</scene>. Meat tenderizer. Old time home remedy for insect, jellyfish, and stingray stings<ref>[http://www.ameriden.com/products/advanced-digestive-enzyme/] Ameridan International</ref>. Who would have thought that a sulfhydryl protease from the latex of the papaya fruit, ''Carica papaya'' and ''Vasconcellea cundinamarcensis'' would have such a practical application beyond proteopedia?
 
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This protease belongs to an extended family of aminopeptidases, dipeptidyl peptidases, endopeptidases, and other enzymes having both exo- and endo-peptidase activity. The inactivated zymogen with N-terminal propeptide regions - providing stability in alkaline environments and enabling proper folding - is activated through removal of the propeptide regions. <ref>PMID: 7845226</ref><ref>PMID: 12188906</ref>
 
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Papain. Lights. Camera. Action!
 
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<Structure load='9pap' size='500' frame='true' align='right' caption='Structure of Papain (PDB entry [[9PAP]])' scene='Sandbox_35/Papain/1'/>
 
==Structure==
==Structure==
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Papain's polypeptide chain consists of 212 amino acid residues which fold to form a groove containing the active site between its two domains. Its
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The <scene name='Sandbox_35/Secondary_structure_colored/1'>secondary structure</scene> of Adenylate Kinase has alpha helicies (purple) and beta sheets (dark pink) that circle around and enclose the non-hydrolysable part of the protein,(seen in the center). This is known as the ligand, which does not experience hydrolysis. These alpha helicies and beta sheets are known as the "backbone" of the protein.
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<scene name='Sandbox_35/Secondary_structure_papain/2'>secondary structure</scene> consists of 17 <scene name='Sandbox_35/2nd_struc_papain_beta/2'>beta sheet</scene> strands and 7 <scene name='Sandbox_35/2nd_struc_papain_helix/2'>alpha helices</scene> giving it a composition 21% and 25% respectively. <ref name="9PAP PDB">[http://www.pdb.org/pdb/explore/explore.do?structureId=9PAP]9PAP PDB</ref> The hydrogen bonds within the alpha helices are shorter than the typical alpha helix because of C=O being directed further away from the helical axis. Moreover, the beta sheet hydrogen bonding constraints and structural angles show great variation; hydrogen bonds in the sheets' central tend to be shorter than on the fringes. Three disulfide bonds, for example <scene name='Sandbox_35/Papain_cys_bond/1'>Cys 22-Cys 63</scene>, serve to hold papain's tertiary structure together. <ref>PMID: 6502713</ref>
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One of the main components of protein structure are the <scene name='Sandbox_35/Secondary_h_bonds2/1'>hydrogen bonds</scene> which are shown in green on this structure. The hydrogen bonds form links between adjacent amino acids, contributing to the protein structure and fold. Hydrogen bonding is an excellent stabilizing factor for the protein! The hydrogen bonds on the beta sheets are in an anti-parallel configuration, which offers stability for the protein.
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==Hydrophobic and Hydrophilic Residue Composition==
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Adenylate kinase is composed of both hydrophobic and hydrophilic residues, and folds accordingly to obtain the optimum environments for the nature of both kinds of residues. The <scene name='Sandbox_35/Secondary_hydrophobs_only_gre/1'>hydrophobic residues</scene> shown in grey are buried within the folded protein, away from contact with the solvent. This action represents the hydrophobic effect taking place, which is mainly driven by entropy. Surrounding the outside of the protein are the <scene name='Sandbox_35/Secondary_hphobic_and_hphilic/1'>hydrophilic residues</scene> (dark green). These residues are polar and can be in caontact with the surrounding solvent in the protein's environment. These residues can either be charged or uncharged, can hydrogen bond with water, and are generally more soluble. They cover the hydrophobic amino acid residues to protect them from the solvent.
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The <scene name='Sandbox_35/Active_site_papain/4'>active site</scene> primarily consist of three main residues Cys25-His159-Asn175 that resembles the catalytic triad of chymotrypsin <ref>PMID: 8140097</ref><ref>PMID: 2397208</ref>. However growing studies are showing that the mechanism behind catalysis may actually involve a double catalytic site - consisting of Cys25-His159-Asn175 '''and''' Cys25-His159-
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==Water and Solvent==
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<scene name='Sandbox_35/Active_site_papain/5'>Asp 158</scene>! It is postulated that "a two-state mechanism" takes place instead of a "single steric mechanism." <ref>PMID: 8140097</ref> In addition, replacement of Asn 175 with other residues such as Ala mutants, reveals a decrease in kcat (less efficiency). Despite this, the rate of hydrolysis is still significantly larger than non-catalytic rates, suggesting a less essential role the Asn 175 plays than originally thought. It should be noted however, that alteration to the 175 side chain resulted in less thermal stability lending thought to Asn 175 playing a more structural conservative role rather than catalytic. <ref>[http://www.jbc.org/content/270/28/16645.abstract] The Journal of Biological Chemistry </ref>
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Water is very important when it comes to protein folding and structure. It determines the conformation of exposed side chains, stabilizes the ends of secondary structures, and occupy positions at active sites where they influence substrate binding and sometimes catalysis. Adenylate kinase in <scene name='Sandbox_35/Secondary_with_water_molecules/1'>solvent</scene> is mostly surrounded by water molecules around the exterior area of the protein; However, it also can utilizes the water molecules to increase efficent substrate binding. The water molecules (light blue) surround the outside of the protein, interacting with the polar hydrophilic residues. However, some water molecules are seen in contact with the ligand (light green center) where the molecules are influencing catalysis.
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==Adenylate Kinase and The Ligand==
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The ligand(dark pink) in the center of the protein has specific residues surrounding it that are also known as the <scene name='Sandbox_35/Secondary_with_ligand_in_cente/1'>ligand contacts</scene>. These residues have polar-charged side chains, which stabilize the ligand. The ligand in Adenylate kinase is a molecule which is able to bind to the protein's specific active site.
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Crystallization of the protease under conditions of 62% (w/w) methanol in water reveals water playing a crucial role in providing structural stability. The 21 internal water molecules surrounding adjacent papain molecules appear to form an encasement that limit protein to protein interaction. <ref>PMID: 6502713</ref>
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==Catalytic Residues==
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The <scene name='Sandbox_35/Secondary_catalytic_residues/1'>catalytic residues</scene> (black) are found in the center of the protein, lining the active site where the ligand binds. These residues, also known as "active site residues", help with recognition of the ligand. The ligand binds with the protein in various ways: hydrogen bonds, hydrophobic interactions, temporary covalent interactions, or a mixture of the mentioned methods. The catalytic residues assist the reaction by acting as proton donors or acceptors. In the big picture, all of this helps the enzyme protein lower the activation energy of the ligand to speed up the reaction efficiently.
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====Distribution of Residues====
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Although Papain has a scattered distribution of <scene name='Sandbox_35/Papain_acid_and_basic_residues/1'>acidic and basic residues</scene>, it can be seen to have more basic residues than acidic, shedding understanding into the application of its use as a digestive supplement. <ref>[http://www.webmd.com/vitamins-supplements/ingredientmono-69-PAPAIN.aspx?activeIngredientId=69&activeIngredientName=PAPAIN] WebMD</ref> Seeing its <scene name='Sandbox_35/Hydrophobicity_papain/3'>polar and non-polar residues</scene> further shows <scene name='Sandbox_35/Papain_polar/1'>polar residues</scene> remaining mostly on the exterior while <scene name='Sandbox_35/Nonpolar_papain/2'>non-polar residues</scene> sequestering near the center. Observations have revealed that the proteins atomic positions are more ordered going from outside toward the center and also disclose the hydrophobic core of the enzyme. <ref>PMID: 6502713 </ref>
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====Ligands interactions and Pseudo Substrates====
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Papain is said to have 29 methanol molecules that encircle around it as <scene name='Sandbox_35/Papain_ligand/1'>ligands</scene>. The polarity of the ligands result in hydrogen bonding interactions, possibly providing further stability for papain structure. <ref>PMID: 6502713</ref>
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<scene name='Sandbox_35/Cathepsin_l_specific_inhibitor/3'>Cathepsin L specific inhibitor</scene> is part of a series known as CLIK inhibitors and was used on Papain for assessment of specificity in inhibition. The difference in structure between Papain-CLIK 148 complex and orginial papain is not very drastic. The changes result primarily from alterations in surface proteins except where a covalent bond is formed between the C2 on <scene name='Sandbox_35/Clik_cys/1'>CLIK 148 and Cys 25</scene>. The primary <scene name='Sandbox_35/Cathepsin_interaction/3'>interactions</scene> between pseudo-substrate/inhibitor and papain were non-water hydrogen bonds and mostly hydrophobic interactions. CLIK 148's binding to the active site of papain is in a non-substrate mode with the main site showing pyrimidine ring interaction between <scene name='Sandbox_35/Clik_trp_177/1'>Trp 177 and CLIK 148</scene>. Hydrogen bonding is observed between the oxygens in <scene name='Sandbox_35/Clik_gly_gln/1'>CLIK 148 to Gln 19 and Gly 66</scene>. Moreover, a water molecule has been observed to be near the His 159 residue enabling greater hydrogen bonding, once again highlighting solvents role in stability. <ref>PMID: 10600517</ref>
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==Catalytic Mechanism==
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[[Image:Papainmech6.jpg|200px|left|thumb| General mechanism of papain catalysis<ref>[http://chemistry.umeche.maine.edu/CHY431/Peptidase10.html] University of Maine</ref>.]] Papain's catalytic mechanism is like serine proteases. Its catalytic triad of residues Cys 25- His159- Arg-175 appear to work with a fourth residue, Gln-19, suspected to be involved in oxyanion hole formation. When a peptide binds to the active site, His-159 deprotonates Cys-25 which in turn attacks the substrate carbonyl carbon. The oxyanion hole then stabilizes the resultant covalent, tetrahedral intermediate. Subsequently, nitrogen in the peptide bond in protonated by His-159 (acting as an acid). This action frees the C-terminal portion of the peptide so that it is released. The entrance of water into the active site then attacks the carbonyl carbon while it is deprotonated by His-159, resulting in another tetrahedral covalent intermediate stabilized through the oxyanion hole. At the end, carbonyl reformation and the Cys-25 sulfur action as the leaving group releases the N-terminal portion of the peptide and later renegerates the enzyme. <ref>[http://chemistry.umeche.maine.edu/CHY431/Peptidase10.html] University of Maine</ref>
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==Fun Trivia==
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Remember the 2002 SARS (Severe Acute Respiratory Syndrome) epidemic that placed global health in a precarious state? On-going research is happening to further understand the mechanisms of this coronavirus so that future steps can be taken for prevention. Its been found that the replication of RNA for this virus is mediated by two viral proteases that have many papain-like characteristics. <ref>PMID: 16306590 </ref>
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==References==
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<references />
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<ref group="xtra">PMID:8140097</ref>
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Current revision

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.

Adenylate Kinase

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Contents

Adenylate Kinase

Adenylate kinase, also known as "ADK", is an enzyme which speeds up the reaction that includes the interconversion of adenine nucleotides. The protein's flexibility allows it to bind to certain substrates known as ligands. Adenylate kinase is known for influencing cellular energy homeostasis.

Structure

The of Adenylate Kinase has alpha helicies (purple) and beta sheets (dark pink) that circle around and enclose the non-hydrolysable part of the protein,(seen in the center). This is known as the ligand, which does not experience hydrolysis. These alpha helicies and beta sheets are known as the "backbone" of the protein. One of the main components of protein structure are the which are shown in green on this structure. The hydrogen bonds form links between adjacent amino acids, contributing to the protein structure and fold. Hydrogen bonding is an excellent stabilizing factor for the protein! The hydrogen bonds on the beta sheets are in an anti-parallel configuration, which offers stability for the protein.

Hydrophobic and Hydrophilic Residue Composition

Adenylate kinase is composed of both hydrophobic and hydrophilic residues, and folds accordingly to obtain the optimum environments for the nature of both kinds of residues. The shown in grey are buried within the folded protein, away from contact with the solvent. This action represents the hydrophobic effect taking place, which is mainly driven by entropy. Surrounding the outside of the protein are the (dark green). These residues are polar and can be in caontact with the surrounding solvent in the protein's environment. These residues can either be charged or uncharged, can hydrogen bond with water, and are generally more soluble. They cover the hydrophobic amino acid residues to protect them from the solvent.

Water and Solvent

Water is very important when it comes to protein folding and structure. It determines the conformation of exposed side chains, stabilizes the ends of secondary structures, and occupy positions at active sites where they influence substrate binding and sometimes catalysis. Adenylate kinase in is mostly surrounded by water molecules around the exterior area of the protein; However, it also can utilizes the water molecules to increase efficent substrate binding. The water molecules (light blue) surround the outside of the protein, interacting with the polar hydrophilic residues. However, some water molecules are seen in contact with the ligand (light green center) where the molecules are influencing catalysis.

Adenylate Kinase and The Ligand

The ligand(dark pink) in the center of the protein has specific residues surrounding it that are also known as the . These residues have polar-charged side chains, which stabilize the ligand. The ligand in Adenylate kinase is a molecule which is able to bind to the protein's specific active site.

Catalytic Residues

The (black) are found in the center of the protein, lining the active site where the ligand binds. These residues, also known as "active site residues", help with recognition of the ligand. The ligand binds with the protein in various ways: hydrogen bonds, hydrophobic interactions, temporary covalent interactions, or a mixture of the mentioned methods. The catalytic residues assist the reaction by acting as proton donors or acceptors. In the big picture, all of this helps the enzyme protein lower the activation energy of the ligand to speed up the reaction efficiently.

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