Sandbox 51: Difference between revisions
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==Active Site== | ==Active Site== | ||
The <scene name='Sandbox_51/Active_site/3'>active site</scene> of the lipase molecule is found in the N-terminal domain (residues 1-336) and contains a <scene name='Sandbox_51/Catalytic_tria/1'>catalytic triad</scene> consisting of a Ser152-His263-Arg176 for the ester hydrolysis reaction (similar to that of a serine protease). The catalytic triad and regions around it are thought to be the best conserved aspects of lipase throughout the lipase family. The active site is covered by a 25-residue helical 'lid' blocking the binding site <ref>Fundamentals of Biochemistry... <scene name='Sandbox_51/Lipase_and_colipase/2'>Lipase and colipase</scene> in complex with a triacylglyceride shows the unique lid (yellow) and beta-5 loop (pink) essential to catalysis. The 10 residue beta-5 loop changes confirmation when colipase binds, exposing lipase's oxyanion hole and hydrophobic surface. Before colipase binding however, lipase is in the <scene name='Sandbox_51/Closed_lid/4'>closed lid</scene> structure where the beta-5 loop (residues 76-84, in pink) and lid (residues 237-261, yellow) protect the oxyanion hole from solvent interaction. The <scene name='Sandbox_51/Mutated_open_ring/6'>open ring</scene> structure is accompanied by peptide shift which increase the hydrophobic surface area initiating the reaction with the lipid. one such important shift is at residues 240-253 (in yellow), in the lid structure, very close to the active site. Also, it is evident from the image that part of the beta-5 loop interacts with colipase in the open state. The lid opening is accompanied by a change in secondary structure from a mostly beta-extended confirmation to a structure where more than half the active site is formed from alpha helices <ref> Thomas, A. etc. "Role of the Lid Hydrophobicity Pattern in Pancreatic Lipase Activity", The Journal of Biological Chemistry, 2005 September 22; 270 (48): 40074-40083. </ref>. | The <scene name='Sandbox_51/Active_site/3'>active site</scene> of the lipase molecule is found in the N-terminal domain (residues 1-336) and contains a <scene name='Sandbox_51/Catalytic_tria/1'>catalytic triad</scene> consisting of a Ser152-His263-Arg176 for the ester hydrolysis reaction (similar to that of a serine protease). The catalytic triad and regions around it are thought to be the best conserved aspects of lipase throughout the lipase family. The active site is covered by a 25-residue helical 'lid' blocking the binding site <ref>Fundamentals of Biochemistry...</ref>. <scene name='Sandbox_51/Lipase_and_colipase/2'>Lipase and colipase</scene> in complex with a triacylglyceride shows the unique lid (yellow) and beta-5 loop (pink) essential to catalysis. The 10 residue beta-5 loop changes confirmation when colipase binds, exposing lipase's oxyanion hole and hydrophobic surface. Before colipase binding however, lipase is in the <scene name='Sandbox_51/Closed_lid/4'>closed lid</scene> structure where the beta-5 loop (residues 76-84, in pink) and lid (residues 237-261, yellow) protect the oxyanion hole from solvent interaction. The <scene name='Sandbox_51/Mutated_open_ring/6'>open ring</scene> structure is accompanied by peptide shift which increase the hydrophobic surface area initiating the reaction with the lipid. one such important shift is at residues 240-253 (in yellow), in the lid structure, very close to the active site. Also, it is evident from the image that part of the beta-5 loop interacts with colipase in the open state. The lid opening is accompanied by a change in secondary structure from a mostly beta-extended confirmation to a structure where more than half the active site is formed from alpha helices <ref> Thomas, A. etc. "Role of the Lid Hydrophobicity Pattern in Pancreatic Lipase Activity", The Journal of Biological Chemistry, 2005 September 22; 270 (48): 40074-40083. </ref>. | ||
[[Image:F1.medium.gif]] | [[Image:F1.medium.gif]] | ||
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==Mechanism== | ==Mechanism== | ||
[[Image:Fatty_acid_breakdown.gif]]<ref>http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/lipoprot.htm </ref> | |||
In addition to the effects of bile salts, Lipase is activated by the coenzyme colipase, which binds to the C-terminal non-catalytic domain. Upon binding, active lipase is stabilized for the hydrophobic interaction with the triacylglycerides <ref>Fundamentals of Biochemistry...</ref>. Colipase must be present for activation of lipase. Lipase activation at the lipid-water interface of triacylglycerides, in the presence of colipase and bile salts, is known as interfacial activation. Colipase is also secreted in the pancreas, but in its inactive form, which must be activated by trypsin before interacting with lipase <ref>"Colipase". Wikipedia: The Free Encyclopedia. 5 July 2011 [http://en.wikipedia.org/wiki/Colipase]</ref>. Colipase and lipase <scene name='Sandbox_51/Contacts/3'>contacts</scene> are at opposite of the active site on the C-terminal, including polar interactions such as <scene name='Sandbox_51/Salt_bridges/2'>salt bridges</scene> and van der waals forces which stabilize the interaction <ref>van Tilbeurgh H, etc."Structure of the pancreatic lipase-procolipase complex", 1992 Sep 10;359(6391):159-62. PMID:1522902.[http://www.proteopedia.org/wiki/index.php/1n8s]</ref>. For the hydrloysis reaction to take place, colipase anchors lipase to the lipid-water membrane of the micelle and a surface change occurs on lipase. Colipase hydrophobic loops interact with the hydrophobic atmosphere of the triacylglyceride initiating the lipase active site binding to the lipid, and lid opening to reveal a more hydrophobic environment for the triacylglycerol. Once colipase is bound, lipase initiates a serine-like hydrolysis involving the His-Asp-Ser active site residues in the catalytic triad <ref>Fundamentals of Biochemistry...</ref>. In the reaction, serine attacks the ester, forming an acyl-enzyme intermediate. The His and Asp residues help to stabilize the oxyanion intermediate through hydrogen bonding. Water enters the active site and reacts to release lipase and free the fatty acid. This acylation and deacylation reaction is usually completely reversible. | In addition to the effects of bile salts, Lipase is activated by the coenzyme colipase, which binds to the C-terminal non-catalytic domain. Upon binding, active lipase is stabilized for the hydrophobic interaction with the triacylglycerides <ref>Fundamentals of Biochemistry...</ref>. Colipase must be present for activation of lipase. Lipase activation at the lipid-water interface of triacylglycerides, in the presence of colipase and bile salts, is known as interfacial activation. Colipase is also secreted in the pancreas, but in its inactive form, which must be activated by trypsin before interacting with lipase <ref>"Colipase". Wikipedia: The Free Encyclopedia. 5 July 2011 [http://en.wikipedia.org/wiki/Colipase]</ref>. Colipase and lipase <scene name='Sandbox_51/Contacts/3'>contacts</scene> are at opposite of the active site on the C-terminal, including polar interactions such as <scene name='Sandbox_51/Salt_bridges/2'>salt bridges</scene> and van der waals forces which stabilize the interaction <ref>van Tilbeurgh H, etc."Structure of the pancreatic lipase-procolipase complex", 1992 Sep 10;359(6391):159-62. PMID:1522902.[http://www.proteopedia.org/wiki/index.php/1n8s]</ref>. For the hydrloysis reaction to take place, colipase anchors lipase to the lipid-water membrane of the micelle and a surface change occurs on lipase. Colipase hydrophobic loops interact with the hydrophobic atmosphere of the triacylglyceride initiating the lipase active site binding to the lipid, and lid opening to reveal a more hydrophobic environment for the triacylglycerol. Once colipase is bound, lipase initiates a serine-like hydrolysis involving the His-Asp-Ser active site residues in the catalytic triad <ref>Fundamentals of Biochemistry...</ref>. In the reaction, serine attacks the ester, forming an acyl-enzyme intermediate. The His and Asp residues help to stabilize the oxyanion intermediate through hydrogen bonding. Water enters the active site and reacts to release lipase and free the fatty acid. This acylation and deacylation reaction is usually completely reversible. | ||
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<applet load='1hpl' size='250' frame='true' align='left' caption='Lipase' /> | <applet load='1hpl' size='250' frame='true' align='left' caption='Lipase' /> | ||
==Inhibition== | ==Inhibition== | ||
The inhibition of pancreatic lipase has serious effects on storage and absorption of fats taken in by the body, and is therefore a potentially strong basis for pharmaceuticals to combat obesity. Because lipase is a part of the serine esterase family, it is inhibited in a similar manner. One such compound is a <scene name='Sandbox_51/Inhibitor/2'>C11 alkyl phosphonate</scene> inhibitor (shown interacting with the lipase-coplipase structure). The inhibitor acts by binding <scene name='Sandbox_51/Inhibitor_at_ser152/3'>Ser152</scene> in the active site inducing conformational changes in the beta-5 loop structures. The alkyl chain fits into the hydrophobic portion of the active lipase-colipase complex mimicking the fatty acid produced through hydrolysis in the normal enzymatic reaction <ref>Egloff, M.P., etc. "The 2.46 angstroms resolution structure of the pancreatic lipase colipase complex inhibited by a C11 alkyl phosphonate."(1995) J. Biochemistry 34: 2751-2762 [http://www.pdb.org/pdb/explore/explore.do?structureId=1lpb]</ref>. Van der waals forces between hydrophobic residues (blue) in the groove stabilize C11P binding, in addition to salt bridging and Hydrogen bonding forces with a cluster of hydrophilic residues (pick) around the Ser152 residue (purple) in the <scene name='Sandbox_51/Inhibitor_pocket/2'>inhibitor binding groove</scene>. <ref>Egloff, M., Marguet, F., Buono, G.,Verger,R.,Cambillau,C., Tilbeurgho,H. The 2.46 A Resolution Structure of the Pancreatic Lipase-Colipase Complex | The inhibition of pancreatic lipase has serious effects on storage and absorption of fats taken in by the body, and is therefore a potentially strong basis for pharmaceuticals to combat obesity. Because lipase is a part of the serine esterase family, it is inhibited in a similar manner. One such compound is a <scene name='Sandbox_51/Inhibitor/2'>C11 alkyl phosphonate</scene> inhibitor (shown interacting with the lipase-coplipase structure). The inhibitor acts by binding <scene name='Sandbox_51/Inhibitor_at_ser152/3'>Ser152</scene> in the active site inducing conformational changes in the beta-5 loop structures. The alkyl chain fits into the hydrophobic portion of the active lipase-colipase complex mimicking the fatty acid produced through hydrolysis in the normal enzymatic reaction <ref>Egloff, M.P., etc. "The 2.46 angstroms resolution structure of the pancreatic lipase colipase complex inhibited by a C11 alkyl phosphonate."(1995) J. Biochemistry 34: 2751-2762 [http://www.pdb.org/pdb/explore/explore.do?structureId=1lpb]</ref>. Van der waals forces between hydrophobic residues (blue) in the groove stabilize C11P binding, in addition to salt bridging and Hydrogen bonding forces with a cluster of hydrophilic residues (pick) around the Ser152 residue (purple) in the <scene name='Sandbox_51/Inhibitor_pocket/2'>inhibitor binding groove</scene>. <ref>Egloff, M., Marguet, F., Buono, G.,Verger,R.,Cambillau,C., Tilbeurgho,H. The 2.46 A Resolution Structure of the Pancreatic Lipase-Colipase Complex Inhibited by a C11 Alkyl Phosphonate? Biochemistry, 1995, 34, 275 1-2762. http://pubs.acs.org.ezproxy.messiah.edu/doi/pdf/10.1021/bi00009a003</ref>. Due to lipase's activity in the digestion and absorption of fat, there has been a growing market for lipase inhibitors for weight loss pharmaceuticals. The most popular is Orlistat (or Xenical®) which is a natural product from ''Streptomyces toxytricini'' and is the hydrogenation product of lipostation- an irreversible lipase inhibitor. This inhibitor also acts by binding Ser152, producing an ester where hydrolyzes so slow that it is practically irreversible <ref>Kordik, C., Reitz, A. "Pharmacological Treatment of Obesity: Therapeutic Strategies" Journal of Medicinal Chemistry, 1999 (42).</ref>. | ||
Inhibited by a C11 Alkyl Phosphonate? Biochemistry, 1995, 34, 275 1-2762. http://pubs.acs.org.ezproxy.messiah.edu/doi/pdf/10.1021/bi00009a003</ref>. | |||
==References== | ==References== | ||
<references /> | <references /> | ||
