Lipase: Difference between revisions

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Lipase is activated by the coenzyme colipase, which binds to the C-terminal non-catalytic domain of lipase. 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 and acts as a bridge between lipase and the lipid. Without colipase present, the accumulation of amphiphiles at the oil/water interface in the duodenum would prevent pancreatic lipase from binding. <ref>Crandall,W., Lowe, M. "Colipase Residues Glu64 and Arg65 Are Essential for Normal Lipase-mediated Fat Digestion in the Presence of Bile Salt Micelles" Journal of Biological Chemistry, 2001, (276) 12505-12512</ref>. Colipase is 10kDA protein, secreted by the pancreas in its inactive form, which must be activated by trypsin before interacting with lipase. Colipase is a small protein cofactor with 5 conserved disulfide bonds <ref>"Colipase". Wikipedia: The Free Encyclopedia. 5 July 2011 [http://en.wikipedia.org/wiki/Colipase]</ref>, and 2 surfaces- a hydrophilic surface (site of lipase C-terminal interaction) and a hydrophobic surface (contains multiple hydrophobic loops to bridge the lipid)<ref>"Colipase Residues..."</ref>. Colipase and lipase <scene name='Lipase/Contacts/1'>contacts</scene> are opposite of the active site on the C-terminal (contacts are regions of pink and yellow, with water molecules shown in darker blue). The enzymes are bound by polar interactions such as <scene name='Lipase/Salt_bridges/2'>salt bridges</scene>, <scene name='Lipase/Hphobic_interactions/1'>hydrophobic interactions</scene> and <scene name='Lipase/Hydrogen_bonds_non_water/1'>hydrogen bonds</scene> <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>.

~~== '''~~Lipase ~~Catalytic~~ Mechanism~~''' ==~~

[[Image:M0218.stg01.gif|200px|left|thumb|Lipase Mechanism Part 1]]

Lipase activation at the lipid-water interface of triacylglycerides, in the presence of colipase and bile salts, is known as interfacial activation. For the hydroloysis reaction to take place, colipase anchors lipase to the lipid-water membrane of the micelle and a surface change occurs on lipase. Colipase's 4 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. Although a diverse array of lipase enzymes are found in nature, occupying diverse protein scaffolds, most are built upon an alpha/beta hydrolase fold<ref>PMID: 1678899</ref><ref>PMID:1409539 </ref> and possess a [[chymotrypsin]]-like <scene name='Lipase/Catalytic_site_outerview/1'>catalytic triad </scene>comprised of an acidic residue, a histidine, and a serine nucleophile. In the case of the images above of a horse pancreatic lipase, the catalytic triad is comprised of <scene name='Lipase/Catalytic_triad/4'>Ser 152, Asp 176 and His 263. </scene><ref>PMID:~~8182745</ref>~~. This catalytic triad functions like most found in nature, first with the Aspartic acid forming a hydrogen bond with His 263, increasing the pKa of the histidine imidazole nitrogen. This allows the histidine to act as a powerful general base and deprotonate the serine. The deprotonated serine then can serve as a nucleophile and attack the ester carbonyl of one of the fatty acids on the 1 or 3 carbons of the glycerol backbone of the lipid substrate. Upon attacking the lipid, a negatively charged tetrahedral intermediate is formed (Reaction 1). ~~It is stabilized in the oxyanion hole by two residues: <scene name='~~Lipase~~/Catalytic_triad_with_oxyanion/~~2'>Phe 77 and Leu 153</scene>. The carbonyl reforms with the glycerol backbone segment acting as the leaving group (Reaction 2). A water molecule then donates a proton to the histidine, creating a reactive hydroxyl anion, which can attack the carbonyl carbon of the lipid, forming another negatively charged tetrahedral intermediate which is stabilized in the oxyanion hole (Reaction 3). Upon reformation of the carbonyl, the catalytic serine is released and monoglyceride and fatty acid monomers diffuse away (Reaction 4).

[[Image:M0218.stg02.gif|200px|left|thumb|Lipase Mechanism Part 2]]

~~Reaction 1:~~

[[Image:M0218.stg03.gif|200px|left|thumb|Lipase Mechanism Part 3]]

[[Image:M0218.~~stg01~~.gif]]

~~Reaction 2:~~

[[Image:M0218.stg04.gif|200px|left|thumb|Lipase Mechanism Part 4]]

[[Image:M0218.~~stg02~~.gif]]

~~Reaction 3~~:

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

[[~~Image~~:~~M0218~~.~~stg03~~.~~gif]]~~

Lipase activation at the lipid-water interface of triacylglycerides, in the presence of colipase and bile salts, is known as interfacial activation. For the hydroloysis reaction to take place, colipase anchors lipase to the lipid-water membrane of the micelle and a surface change occurs on lipase. Colipase's 4 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. Although a diverse array of lipase enzymes are found in nature, occupying diverse protein scaffolds, most are built upon an alpha/beta hydrolase fold<ref>PMID: 1678899</ref><ref>PMID:1409539 </ref> and possess a [[chymotrypsin]]-like <scene name='Lipase/Catalytic_site_outerview/1'>catalytic triad </scene>comprised of an acidic residue, a histidine, and a serine nucleophile. In the case of the images above of a horse pancreatic lipase, the catalytic triad is comprised of <scene name='Lipase/Catalytic_triad/4'>Ser 152, Asp 176 and His 263. </scene><ref>PMID:8182745</ref>. This catalytic triad functions like most found in nature, first with the Aspartic acid forming a hydrogen bond with His 263, increasing the pKa of the histidine imidazole nitrogen. This allows the histidine to act as a powerful general base and deprotonate the serine. The deprotonated serine then can serve as a nucleophile and attack the ester carbonyl of one of the fatty acids on the 1 or 3 carbons of the glycerol backbone of the lipid substrate. Upon attacking the lipid, a negatively charged tetrahedral intermediate is formed (Reaction 1). It is stabilized in the oxyanion hole by two residues: <scene name='Lipase/Catalytic_triad_with_oxyanion/2'>Phe 77 and Leu 153</scene>. The carbonyl reforms with the glycerol backbone segment acting as the leaving group (Reaction 2). A water molecule then donates a proton to the histidine, creating a reactive hydroxyl anion, which can attack the carbonyl carbon of the lipid, forming another negatively charged tetrahedral intermediate which is stabilized in the oxyanion hole (Reaction 3). Upon reformation of the carbonyl, the catalytic serine is released and monoglyceride and fatty acid monomers diffuse away (Reaction 4).

~~Reaction 4:~~

~~[[Image:M0218.stg04.gif]]~~

== '''Inhibition of Pancreatic Lipase''' ==

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 Lipase is activated by the coenzyme colipase, which binds to the C-terminal non-catalytic domain of lipase.  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 and acts as a bridge between lipase and the lipid.  Without colipase present, the accumulation of amphiphiles at the oil/water interface in the duodenum would prevent pancreatic lipase from binding. <ref>Crandall,W., Lowe, M. "Colipase Residues Glu64 and Arg65 Are Essential for Normal Lipase-mediated Fat Digestion in the Presence of Bile Salt Micelles" Journal of Biological Chemistry, 2001, (276) 12505-12512</ref>.  Colipase is 10kDA protein, secreted by the pancreas in its inactive form, which must be activated by trypsin before interacting with lipase.  Colipase is a small protein cofactor with 5 conserved disulfide bonds <ref>"Colipase". Wikipedia: The Free Encyclopedia. 5 July 2011 [http://en.wikipedia.org/wiki/Colipase]</ref>, and 2 surfaces- a hydrophilic surface (site of lipase C-terminal interaction) and a hydrophobic surface (contains multiple hydrophobic loops to bridge the lipid)<ref>"Colipase Residues..."</ref>.  Colipase and lipase <scene name='Lipase/Contacts/1'>contacts</scene> are opposite of the active site on the C-terminal (contacts are regions of pink and yellow, with water molecules shown in darker blue).  The enzymes are bound by polar interactions such as <scene name='Lipase/Salt_bridges/2'>salt bridges</scene>, <scene name='Lipase/Hphobic_interactions/1'>hydrophobic interactions</scene> and <scene name='Lipase/Hydrogen_bonds_non_water/1'>hydrogen bonds</scene> <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>.
-== '''Lipase Catalytic Mechanism''' ==
+[[Image:M0218.stg01.gif|200px|left|thumb|Lipase Mechanism Part 1]]
-Lipase activation at the lipid-water interface of triacylglycerides, in the presence of colipase and bile salts, is known as interfacial activation.   For the hydroloysis reaction to take place, colipase anchors lipase to the lipid-water membrane of the micelle and a surface change occurs on lipase.  Colipase's 4 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.  Although a diverse array of lipase enzymes are found in nature, occupying diverse protein scaffolds, most are built upon an alpha/beta hydrolase fold<ref>PMID: 1678899</ref><ref>PMID:1409539 </ref>  and possess a [[chymotrypsin]]-like <scene name='Lipase/Catalytic_site_outerview/1'>catalytic triad </scene>comprised of an acidic residue, a histidine, and a serine nucleophile. In the case of the images above of a horse pancreatic lipase, the catalytic triad is comprised of <scene name='Lipase/Catalytic_triad/4'>Ser 152, Asp 176 and His 263. </scene><ref>PMID:8182745</ref>.  This catalytic triad functions like most found in nature, first with the Aspartic acid forming a hydrogen bond with His 263, increasing the pKa of the histidine imidazole nitrogen. This allows the histidine to act as a powerful general base and deprotonate the serine. The deprotonated serine then can serve as a nucleophile and attack the ester carbonyl of one of the fatty acids on the 1 or 3 carbons of the glycerol backbone of the lipid substrate.  Upon attacking the lipid, a negatively charged tetrahedral intermediate is formed (Reaction 1).  It is stabilized in the oxyanion hole by two residues:  <scene name='Lipase/Catalytic_triad_with_oxyanion/2'>Phe 77 and Leu 153</scene>.  The carbonyl reforms with the glycerol backbone segment acting as the leaving group (Reaction 2).  A water molecule then donates a proton to the histidine, creating a reactive hydroxyl anion, which can attack the carbonyl carbon of the lipid, forming another negatively charged tetrahedral intermediate which is stabilized in the oxyanion hole (Reaction 3).  Upon reformation of the carbonyl, the catalytic serine is released and monoglyceride and fatty acid monomers diffuse away (Reaction 4).
+[[Image:M0218.stg02.gif|200px|left|thumb|Lipase Mechanism Part 2]]
-Reaction 1:
+[[Image:M0218.stg03.gif|200px|left|thumb|Lipase Mechanism Part 3]]
-[[Image:M0218.stg01.gif]]
-Reaction 2:
+[[Image:M0218.stg04.gif|200px|left|thumb|Lipase Mechanism Part 4]]
-[[Image:M0218.stg02.gif]]
-Reaction 3:
+== '''Lipase Catalytic Mechanism''' ==
-[[Image:M0218.stg03.gif]]
+Lipase activation at the lipid-water interface of triacylglycerides, in the presence of colipase and bile salts, is known as interfacial activation.   For the hydroloysis reaction to take place, colipase anchors lipase to the lipid-water membrane of the micelle and a surface change occurs on lipase.  Colipase's 4 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.  Although a diverse array of lipase enzymes are found in nature, occupying diverse protein scaffolds, most are built upon an alpha/beta hydrolase fold<ref>PMID: 1678899</ref><ref>PMID:1409539 </ref>  and possess a [[chymotrypsin]]-like <scene name='Lipase/Catalytic_site_outerview/1'>catalytic triad </scene>comprised of an acidic residue, a histidine, and a serine nucleophile. In the case of the images above of a horse pancreatic lipase, the catalytic triad is comprised of <scene name='Lipase/Catalytic_triad/4'>Ser 152, Asp 176 and His 263. </scene><ref>PMID:8182745</ref>.  This catalytic triad functions like most found in nature, first with the Aspartic acid forming a hydrogen bond with His 263, increasing the pKa of the histidine imidazole nitrogen. This allows the histidine to act as a powerful general base and deprotonate the serine. The deprotonated serine then can serve as a nucleophile and attack the ester carbonyl of one of the fatty acids on the 1 or 3 carbons of the glycerol backbone of the lipid substrate.  Upon attacking the lipid, a negatively charged tetrahedral intermediate is formed (Reaction 1).  It is stabilized in the oxyanion hole by two residues:  <scene name='Lipase/Catalytic_triad_with_oxyanion/2'>Phe 77 and Leu 153</scene>.  The carbonyl reforms with the glycerol backbone segment acting as the leaving group (Reaction 2).  A water molecule then donates a proton to the histidine, creating a reactive hydroxyl anion, which can attack the carbonyl carbon of the lipid, forming another negatively charged tetrahedral intermediate which is stabilized in the oxyanion hole (Reaction 3).  Upon reformation of the carbonyl, the catalytic serine is released and monoglyceride and fatty acid monomers diffuse away (Reaction 4).
-Reaction 4:
-[[Image:M0218.stg04.gif]]
 == '''Inhibition of Pancreatic Lipase''' ==