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| | == alfa amilasas == | | == alfa amilasas == |
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| - | Las <scene name='80/807512/Amilasa1/1'>alfa amilasas</scene> son enzimas globulares que se secretan en la saliva o en el jugo pancreático de nuestro organismo. El sustrato, <scene name='80/807512/Amilasa2/1'>la amilosa</scene>, es una molécula larga y lineal. En consecuencia, el centro activo de la alfa-amilasa forma una <scene name='80/807512/Amilasa3/1'>hendidura</scene> a la que se une el sustrato. Si nos fijamos en los <scene name='80/807512/Amilasa4/1'>aminoácidos del centro activo</scene> vemos que actúan en la parte media del sustrato unido a la enzima. En cambio, en la celulosas, el enlace entre glucosas <scene name='80/807512/Celulosa1/1'>es beta</scene> generando estructuras planas. Aquí vemos dos cadenas de <scene name='80/807512/Celulosa2/1'>celulosa</scene> formando una estructura plana | + | Las <scene name='80/807512/Amilasa1/4'>alfa amilasas</scene> son enzimas globulares que se secretan en la saliva o en el jugo pancreático de nuestro organismo. Actúan sobre enlaces alfa 1-4 entre dos moléculas de glucosa, y con la condición de que el enlace se encuentre en un poliglícido de glucosa y alejado de extremos o puntos de ramificación. Vemos la proteína y un segmento de amilosa (rojo) unido al centro activo |
| | + | ===El sustrato: amilosa y amilopectina=== |
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| - | == Disease == | + | El sustrato, puede ser <scene name='80/807512/Amilasa2/2'>la amilosa</scene>, que es una macromelécula lineal pero que debido a los enlaces alfa adopta un estructura helicoidal. El otro componente del almidón es la <scene name='80/807512/Amilopectina1/3'>amilopectina</scene>. Se observa claramente la ramificación |
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| - | == Relevance == | + | ===Centro activo y mecanismo de acción=== |
| | + | El centro activo de la alfa-amilasa forma una <scene name='80/807512/Amilasa3/1'>hendidura</scene> a la que se une el sustrato. Si nos fijamos en los <scene name='80/807512/Amilasa4/1'>aminoácidos del centro activo</scene> vemos que actúan en la parte media del sustrato unido a la enzima. Esto explica que la amilasa no actúe sobre enlaces en un extremo del poliglícido ni sobre diglícidos o triglícidos. |
| | + | En las celulosas, el enlace entre glucosas <scene name='80/807512/Celulosa1/1'>es beta</scene> generando estructuras planas. Aquí vemos dos cadenas de <scene name='80/807512/Celulosa2/1'>celulosa</scene> formando una estructura plana y muy compacta. Tan compacta que resulta impermeable a las moléculas de agua |
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| - | == Structural highlights == | + | == La lipasa pancreática == |
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| - | This is a sample scene created with SAT to <scene name="/12/3456/Sample/1">color</scene> by Group, and another to make <scene name="/12/3456/Sample/2">a transparent representation</scene> of the protein. You can make your own scenes on SAT starting from scratch or loading and editing one of these sample scenes.
| + | La <scene name='80/807512/Lipasa1/4'>lipasa pancreática</scene> es una enzima globular relativamente pequeña y soluble en medios acuosos. Aquí vemos un pseudosubstrato (naranja) unido al centro activo de la enzima. Esta zona de la enzima entrará en contacto con la interfase de la emulsión, dentro del jugo intestinal y llevará a cabo la hidrólisis del enlace ester carboxílico de los triglicéridos. |
| | + | Si coloreamos la enzima según la <scene name='80/807512/Lipasa2/1'>polaridad (polares lila, apolares gris)</scene> de sus aminoácidos podemos observar el patrón típico de una proteína globular soluble en medios acuosos. Al cortar la proteína por la mitad observamos como los polares quedan por fuera y los apolares en el interior. |
| | + | Esto plantea el problema de que el <scene name='80/807512/Lipasa3/1'>centro activo y la enzima en general</scene>, durante la digestión, se ven expuestas al efecto inactivador de las sales biliares (detergentes) y de la interfase lípido-agua. |
| | + | La solución la aporta la <scene name='80/807512/Lipasa4/1'>colipasa</scene>, que se une a la lipasa y la protege de la interfase. Se observa la proteína en colores diferentes de la lipasa con una parte hacia el frente de la interfase rica en aminoácidos apolares (gris claro) |
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| - | </StructureSection> | |
| - | == References == | |
| - | <references/> | |
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| - | <StructureSection load='7gch' size='350' side='right' scene='38/387136/Bovine_chymotrypsin_overview/1' caption='Bovine γ-chymotrypsin A (residues 1-13 in pink, 16-146 in cyan, 149-245 in gold) complex with inhibitor (PDB code [[7gch]]) '>
| + | == Disease == |
| - | [[Image:2ea3.png|left|200px|thumb|Crystal Structure of ''Cellulomonas Bogoriensis'' Chymotrypsin [[2ea3]]]]
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| - | __TOC__
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| - | == Function ==
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| - | [[Chymotrypsin]] (Chy or α-Chy) is a digestive enzyme containing an active serine residue, which helps to digest proteins in our food. Other related proteases are crucial for blood clotting ([http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=stryer&part=A1378&rendertype=figure&id=A1401 thrombin and other proteases]), for the AIDS virus metabolism ([http://www.proteopedia.org/wiki/index.php/Hiv_protease HIV protease]) and for many other processes relevant to human health and agriculture. Chymotrypsin cleaves peptide bonds of proteins where the amide side of the bond is an aromatic amino acid like tyrosine, phenylalanine or tryptophan. Bovine Chy is found in 2 forms: A and B. The 2 forms have different proteolytic characteristics. '''γ-Chy''' is a covalent acyl adduct of α-Chy.The image at the left is the crystal structure of chymotrypsin from ''Cellulomonas Bogoriensis'' ([[2ea3]]) with sulfate ions.<ref>PMID:3555886</ref><br /> Some additional details in<br />
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| - | *[[Molecular Playground/Chymotrypsin]]<br />
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| - | *[[Protease]]<br />
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| - | *[[Serine Proteases]].
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| - | == Overview == | + | == Relevance == |
| - | While chymotrypsin occurs in many organisms, the most-studied chymotrypsin is that from cows (bovine chymotrypsin), shown here with an inhibitor molecule (shown in [[CPK]]-colored ball and stick) bound to the active site (<scene name='38/387136/Bovine_chymotrypsin_overview/1'>default scene</scene>). It is synthesized as a single polypeptide chain of 245 amino acids, called chymotrypsinogen, which is inactive. The enzyme is activated by one cleavage by trypsin and two cleavages by chymotrypsin (autolytic cleavages) that result in the loss of four amino acids from the remaining three polypeptides, which are shown here in turquoise, beige, and violet. These three chains are held together by <scene name='38/387136/Bovine_chymotrypsin_overview/5'> two inter-chain disulfide bonds</scene>. The bonded cysteine residues are shown in space fill with yellow sulfur atoms. There also three <scene name='38/387136/Bovine_chymotrypsin_overview/6'>intra-chain disulfide bonds</scene>. Here chymotrypsin is shown in cartoon with pink α-helices and yellow β-strands, and this shows that it is mainly composed of <scene name='38/387136/Bovine_chymotrypsin_overview/7'>two beta barrels</scene>.
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| - | == Substrate-binding and Active Sites == | + | == Structural highlights == |
| - | [[Image:LPFstructure.jpg|left]]Features of the substrate-binding and active sites can be seen in the structure of bovine chymotrypsin bound to the inhibitor N-acetyl-L-leucyl-L-phenylalanyl trifuoromethyl ketone, which resembles a peptide substrate (see structure in left figure). The colored backgrounds in the figure indicate the four components of structure and shows the bond (yellow on black background) that is position to be cleaved.
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| - | Here is chymotrypsin (space fill) with the inhibitor (CPK ball & stick) showing the <scene name='38/387136/Bovine_chymotrypsin_overview/3'>inhibitor sitting in the active site</scene>. Note the active site is in a depression on the surface of the enzyme. Chymotrypsin contains three residues, Ser 195, His 57 and Asp 102, which are known as its <scene name='38/387136/Bovine_chymotrypsin_active_sit/4'>catalytic triad</scene>, shown in CPK ball and stick in this close up of the active site. Similar three-dimensional arrangements of a serine, a histidine and an aspartate are observed in many other proteases, and the role of these three residues in catalysis has been studied extensively. Serine acts as a nucleophile (contributing the electron pair for a new bond) attacking the carbonyl carbon of the peptide bond to be hydrolyzed. Histidine and aspartate turn serine into a better nucleophile by assisting in removing a hydrogen ion from serine.
| + | This is a sample scene created with SAT to <scene name="/12/3456/Sample/1">color</scene> by Group, and another to make <scene name="/12/3456/Sample/2">a transparent representation</scene> of the protein. You can make your own scenes on SAT starting from scratch or loading and editing one of these sample scenes. |
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| - | The <scene name='38/387136/Bovine_chymotrypsin_active_sit/1'>substrate-binding site</scene>, can be seen in this view with the inhibitor in light gray ball & stick with its phenyl group in orchid. By moving the structure back and forth with your mouse, it is easy to see that the phenyl group is located in the hydrophobic binding pocket of the enzyme. This binding pocket determines the enzyme's preference for cleavage of peptides on the C-terminal side of aromatic residues.
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| - | This view shows the <scene name='38/387136/Bovine_chymotrypsin_active_sit/3'>carbonyl group of the inhibitor</scene> in CPK colors. The triflouromethyl group is bound to the carbonyl carbon via the yellow bond. In a peptide substrate, the triflouromethyl group would be replaced by the first amino acid residue of the rest of the peptide chain, and the yellow bond would be the bond that is cleaved. The carbonyl carbon of the inhibitor is 1.52 Å away from the side chain oxygen of serine 195, and this indicates they are covalently bound (bond indicated by dotted line). Thus, this structure is similar to the '''tetrahedral intermediate''' that is formed during the cleavage reaction. The negative charge that develops on the carbonyl oxygen of the substrate is stabilized by hydrogen bonds to the backbone nitrogens of Ser 195 and Gly 193, shown in blue spacefill. The hydrogen atoms involved in these hydrogen bonds are not shown.
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| - | == 3D Structures of Chymotrypsin ==
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| - | [[Chymotrypsin 3D structures]]
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| | </StructureSection> | | </StructureSection> |
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| | == References == | | == References == |
| | <references/> | | <references/> |
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| - | ==Further reading== | |
| - | You can learn more about chymotrypsin structure, function and regulation in this publicly available [http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=stryer&part=A1170#A1171 chapter] of the Biochemistry textbook by Berg, Tymoczka and Stryer. | |
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| - | [[Category:Topic Page]] | |
