Sandbox 44: Difference between revisions
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<p>When lipid micelles are present, the 25-residue "lid" over the active site undergoes a conformational changes in order that the active site may be exposed. At the same time, the beta 5 loop (consisting of 10 residues) also undergoes a conformational change to make an oxyanion hole for the enzyme, thereby creating a hydrophobic surface close to the active site entryway. This beta 5 loop had previously (before the coenzyme's binding) served to protect the oxyanion hole, but now it can reveal the hole for the reaction to proceed.<ref>Lennens, M. & Lowe, Mark. "A surface loop covering the active site of human pancreatic lipase influences interfacial activation and lipid binding." 14 Oct, 1994 The Journal of Biological Chemistry, 269, 25470-25474. [http://www.jbc.org/content/269/41/25470.full.pdf+html]</ref> As colipase binds, it forms three additional hydrogen bonds to the recently opened "lid" of the active site so as to most effectively stabilize the lid in its open position.<ref>Eydoux, C., et al. "Structure of human pancreatic lipase-related protein 2 with the lid in an open conformation." 15 Aug, 2008. DOI: 10.1021/bi8005576 [http://pubs.acs.org/doi/abs/10.1021/bi8005576]</ref> After the binding of colipase, lipase completes a hydrolysis very similar to that of a serine protease through the use of its catalytic triad. This hydrolysis eventually releases the desired broken-down lipid products.</p> | <p>When lipid micelles are present, the 25-residue "lid" over the active site undergoes a conformational changes in order that the active site may be exposed. At the same time, the beta 5 loop (consisting of 10 residues) also undergoes a conformational change to make an oxyanion hole for the enzyme, thereby creating a hydrophobic surface close to the active site entryway. This beta 5 loop had previously (before the coenzyme's binding) served to protect the oxyanion hole, but now it can reveal the hole for the reaction to proceed.<ref>Lennens, M. & Lowe, Mark. "A surface loop covering the active site of human pancreatic lipase influences interfacial activation and lipid binding." 14 Oct, 1994 The Journal of Biological Chemistry, 269, 25470-25474. [http://www.jbc.org/content/269/41/25470.full.pdf+html]</ref> As colipase binds, it forms three additional hydrogen bonds to the recently opened "lid" of the active site so as to most effectively stabilize the lid in its open position.<ref>Eydoux, C., et al. "Structure of human pancreatic lipase-related protein 2 with the lid in an open conformation." 15 Aug, 2008. DOI: 10.1021/bi8005576 [http://pubs.acs.org/doi/abs/10.1021/bi8005576]</ref> After the binding of colipase, lipase completes a hydrolysis very similar to that of a serine protease through the use of its catalytic triad. This hydrolysis eventually releases the desired broken-down lipid products.</p> | ||
<p>Chemically, the mechanism of triacylglycerol by lipase is achieved only through the reactions of the His, Ser, and Asp residues of the active site, as well as with aid from the stabilizing effects of nearby Phe 77 and Leu 153 found in the oxyanion hole.</p> | <p>Chemically, the mechanism of triacylglycerol by lipase is achieved only through the reactions of the His, Ser, and Asp residues of the active site, as well as with aid from the stabilizing effects of nearby Phe 77 and Leu 153 found in the oxyanion hole.</p> | ||
<p>[[Image:lipase.gif]]<ref>Reetz, M. "Controlling the enantioselectivity of enzymes by directed evolution: Practical and theoretical ramifications." 20 Apr 2004, doi: 10.1073/pnas.0306866101 [http://www.pnas.org/content/101/16/5716.full]</ref> | <p>[[Image:lipase.gif]]<ref>Reetz, M. "Controlling the enantioselectivity of enzymes by directed evolution: Practical and theoretical ramifications." 20 Apr 2004, doi: 10.1073/pnas.0306866101 [http://www.pnas.org/content/101/16/5716.full]</ref></p> | ||
<p>Mechanistically, the reaction begins as Asp abstracts a proton from the His residue, which in turn acts as a base by deprotonating Ser. This deprotonation allows Ser to attack the carbonyl of the substrate group, which then shifts its electrons in a manner so that its oxygen now has a negative charge, generating a covalent bond between the carbonyl cation and Ser. This formation is what is referred to as the "oxyanion" intermediate, a tetrahedral intermediate with a negative charge on the central oxygen. It is at this step that Phe 77 and Leu 153 stabilize the oxyanion intermediate in its oxyanion hole. However, the carbonyl soon is reformed, which breaks the bond and generates the acyl enzyme intermediate and an alcohol group. This acyl enzyme intermediate is, in turn, attacked at its carbonyl carbon, leading to the production of a regenerated Ser residue and a fatty acid, hence displaying the mechanism by which lipase cuts a large triacylglyceride into significantly smaller fatty acids.</p> | |||
</StructureSection> | </StructureSection> | ||
==Applications== | ==Applications== | ||
<StructureSection load='1hpl' size=' | <StructureSection load='1hpl' size='300' side='right' caption='Lipase (PDB entry [[1hpl]])' scene=''> | ||
Since human pancreatic lipase plays such a vital function on the breakdown and storage of fats in the human body, there are no doubt a wealth of applications stemming from lipase manipulation. The inhibition of lipase, in particular, has been studied in great detail by pharmaceutical companies, as when lipase in inhibited, it cannot properly store and absorb fat. If the human body cannot store fat properly, it likely will lose weight- naturally a result upon which pharmaceutical companies can capitalize today in our obese society! <p> | Since human pancreatic lipase plays such a vital function on the breakdown and storage of fats in the human body, there are no doubt a wealth of applications stemming from lipase manipulation. The inhibition of lipase, in particular, has been studied in great detail by pharmaceutical companies, as when lipase in inhibited, it cannot properly store and absorb fat. If the human body cannot store fat properly, it likely will lose weight- naturally a result upon which pharmaceutical companies can capitalize today in our obese society! <p> | ||
One particular such <scene name='Sandbox_44/Inhibitor/1'>lipase inhibitor</scene> under research is a C11 alkyl phosphonate compound that inhibits lipase through its binding of Ser 152 in the active site. <ref>1HPL PDB [http://www.pdb.org/pdb/explore/explore.do?structureId=1LPB] </ref> The inhibitor fits into a hydrophobic groove within the molecule and thus is believed by scientists to be a mimic of a fatty acid which would have been produced from the binding of a triacylglyceride and the enzyme. Such devious maneuvers by lipase inhibitors may truly be the face of tomorrow's weight-loss drugs as they prevent the storage and absorption of fats by the body. Of course, caution must naturally be taken with the promise of such drugs, as a complete lack of fat absorption and/or storage by the body could be potentially fatal.</p><p> | One particular such <scene name='Sandbox_44/Inhibitor/1'>lipase inhibitor</scene> under research is a C11 alkyl phosphonate compound that inhibits lipase through its binding of Ser 152 in the active site. <ref>1HPL PDB [http://www.pdb.org/pdb/explore/explore.do?structureId=1LPB] </ref> The inhibitor fits into a hydrophobic groove within the molecule and thus is believed by scientists to be a mimic of a fatty acid which would have been produced from the binding of a triacylglyceride and the enzyme. Such devious maneuvers by lipase inhibitors may truly be the face of tomorrow's weight-loss drugs as they prevent the storage and absorption of fats by the body. Of course, caution must naturally be taken with the promise of such drugs, as a complete lack of fat absorption and/or storage by the body could be potentially fatal.</p> | ||
<p>There are also significant clinical applications of pancreatic lipase, as we know it to be in very low concentration in serum in the duodenum. If something goes wrong in the pancreas and it begins to behave irregularly, such as is the case in pancreatitis and/or pancreatic adenocarcinoma, the concentration of pancreatic lipase in the duodenum will be extreme, as the pancreas may initiate an autolysis, resulting in far more secretion of pancreatic lipase into the duodenum than is usual, necessary, or healthy. Since this is a dangerous condition, careful monitoring of the serum concentration of lipase in the pancreas is a useful way to diagnose pancreatitis.<ref>"Pancreatic lipase." Wikipedia, the free encyclopedia</ref></p> | |||
</StructureSection> | </StructureSection> | ||
==References== | ==References== | ||
<references /> | <references /> | ||
