Lipase: Difference between revisions

Proteopedia Page Contributors and Editors (what is this?)Proteopedia Page Contributors and Editors (what is this?)

David Canner, Joel L. Sussman, Eran Hodis, Alexander Berchansky, Michal Harel, Stephanie Schell, Natalie Ziegler, Quinn R. Murray, Katelyn Clark, Leben Tadesse, Eric Martz

@@ Line 21: / Line 21: @@
 == '''Lipase Catalytic Mechanism''' ==
-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 which causes a surface change on lipase.  Colipase's 4 hydrophobic loops interact with the hydrophobic atmosphere of the triacylglyceride. This initiates active site binding to the lipid, and lid opening to reveal a more hydrophobic environment for the triacylglycerol.  This in turn, allows the triacylglycerol to interact with key active site residues like the catalytic triad.  A diverse array of lipase enzymes can be found in nature. Though the different forms occupy 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 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, aspartic acid forms 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>.
+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 which causes a surface change on lipase.  Colipase's four hydrophobic loops interact with the hydrophobic atmosphere of the triacylglyceride. This initiates active site binding to the lipid, and lid opening to reveal a more hydrophobic environment for the triacylglycerol.  This in turn, allows the triacylglycerol to interact with key active site residues like the catalytic triad.  A diverse array of lipase enzymes can be found in nature. Though the different forms occupy 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 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, aspartic acid forms 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>.
 [[Image:M0218.stg01.gif]]
@@ Line 27: / Line 27: @@
 [[Image:M0218.stg02.gif]]
-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).
+A water molecule then donates a proton to the histidine, creating a reactive hydroxyl anion. The hydroxyl anion can then attack the carbonyl carbon of the lipid, forming another negatively charged tetrahedral intermediate which is stabilized in the oxyanion hole (Reaction 3).
 [[Image:M0218.stg03.gif]]
@@ Line 38: / Line 38: @@
 MUP was shown to be <scene name='Lipase/C11p_bound_h_phobics/1'>further stabilized</scene> by van der Waals contacts with hydrophobic side chains Ala 178, Phe 215, Pro l80, Tyr ll4, Leu 213 (shown in blue).
+== '''Protein - Substrate Interactions''' ==
+Lipase binds <scene name='Lipase/Substrate_contacts/1'>substrates such as cholesteryl linoleate</scene> with numerous hydrophobic contacts.  As is seen here, the lipase interacts with the alkyl group of cholesteryl linoleate via a hydrophobic rift within the protein.  This rift orients the molecule to optimize the lipolysis reaction.
-== '''Protein - Substrate Interactions''' ==
-Lipase binds <scene name='Lipase/Substrate_contacts/1'>substrates such as cholesteryl linoleate</scene> with numerous hydrophobic contacts.  As is seen here the lipase interacts with the alkyl group of cholesteryl linoleate via a hydrophobic rift within the protein.  This rift orients the molecule to optimize the lipolysis reaction.
 Shown in this scene is lipase from the yeast ''Candida rugosa'' in <scene name='Lipase/Complex_2/1'>complex</scene> with two molecules of cholesteryl linoleate (grey).  The active site residues including Ser152, Asp176, and His263 are shown in red stick representation.  Lipase can accommodate two lipid molecules due to the fact that it's two identical subunits catalyze an identical reaction.  One lipase molecule can catalyze two lipolysis reactions at a time.
 == '''Clinical Significance''' ==
 Pancreatic lipase is secreted into the duodenum through the duct system of the pancreas. In a healthy individual, it is at very low concentration in serum. Under extreme disruption of pancreatic function, such as pancreatitis or pancreatic cancer, the pancreas may begin to digest itself and release pancreatic enzymes including pancreatic lipase into serum. Measurement of serum concentration of pancreatic lipase can therefore aid in diagnosis of acute pancreatitis.<ref>"Pancreatic lipase". Wikipedia: The Free Encyclopedia. 7 Nov 2011 [http://en.wikipedia.org/wiki/Pancreatic_lipase]</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 which 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>.
 </StructureSection>