Lipase: Difference between revisions
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== '''Lipase Catalytic Mechanism''' == | == '''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 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>. | 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>. | ||
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The carbonyl reforms with the glycerol backbone segment acting as the leaving group (Reaction 2). | The carbonyl reforms with the glycerol backbone segment acting as the leaving group (Reaction 2). | ||