Sandbox 49

From Proteopedia

(Difference between revisions)
Jump to: navigation, search
Line 12: Line 12:
==Lipase Active Sites==
==Lipase Active Sites==
-
The Lipase Active Sites consists of a catalytic triad of residues: Ser 152, Asp 176, and His 263. Residues Phe 77 and Leu 153 are also important for the mechanism of Lipase, functioning as residues to aid in the stabilization of the oxyanion. The catalytic triad is covered by a “lid” that protects the active site of the enyzyme, and prevents the binding of substrate when it is closed and covering the active site, the open lid is stabilized by the formation of hydrogen bonds to neighboring residues. In total lipase has 2 active sites, 1 for each of the domains that make up the enzyme.
+
The <scene name='Sandbox_49/Lipase_active_sites_final/1'>Lipase active sites</scene> consists of a catalytic triad of residues: Ser 152, Asp 176, and His 263. Residues Phe 77 and Leu 153 are also important for the mechanism of Lipase, functioning as residues to aid in the stabilization of the oxyanion. The catalytic triad is covered by a “lid” that protects the active site of the enyzyme, and prevents the binding of substrate when it is closed and covering the active site, the open lid is stabilized by the formation of hydrogen bonds to neighboring residues. In total lipase has 2 active sites, 1 for each of the domains that make up the enzyme.
==Mechanism==
==Mechanism==
Line 34: Line 34:
==Inhibition and Activation==
==Inhibition and Activation==
C11 alkyl phosphate is an effective inhibitor of pancreatic lipase, it was synthesized in an attempt to gain a better understanding of the enzyme’s active site. The inhibitor’s alkyl chain fits into the hydrophobic groove of the active site’s catalytic triad and covalently binds to Ser 152, but instead of reacting like the normal triacylglyceride substrate the inhibitor does not react and stays bound, effectively destroying the ability of the enzyme to function.
C11 alkyl phosphate is an effective inhibitor of pancreatic lipase, it was synthesized in an attempt to gain a better understanding of the enzyme’s active site. The inhibitor’s alkyl chain fits into the hydrophobic groove of the active site’s catalytic triad and covalently binds to Ser 152, but instead of reacting like the normal triacylglyceride substrate the inhibitor does not react and stays bound, effectively destroying the ability of the enzyme to function.
 +
Bile salts are steroids important for further degradation of the triacylglycerides processed by pancreatic lipase, however they are also inhibitors of the lipase as well. To prevent this inhibition the cofactor colipase is vital. Colipase is secreted by the pancreas in its inactive form procolipase, upon activation the protein binds to the noncatalytic C terminal arm of Lipase to activate the protein.
Bile salts are steroids important for further degradation of the triacylglycerides processed by pancreatic lipase, however they are also inhibitors of the lipase as well. To prevent this inhibition the cofactor colipase is vital. Colipase is secreted by the pancreas in its inactive form procolipase, upon activation the protein binds to the noncatalytic C terminal arm of Lipase to activate the protein.

Revision as of 16:59, 15 March 2012

Please do NOT make changes to this Sandbox. Sandboxes 30-60 are reserved for use by Biochemistry 410 & 412 at Messiah College taught by Dr. Hannah Tims during Fall 2012 and Spring 2013.

PDB ID 1hpl

Drag the structure with the mouse to rotate

Contents

Introduction

Lipases represent a critical class of enzymes that functions in the breakdown of triacylglycerides. Produced by the pancreas, lipase catalyzes the hydrolysis of triacylglyercols at their 1 and 3 carbons, resulting the in the production of 2-monoacylglycerols and free fatty acids. Modeled here is horse pancreatic lipase.

Structure

Lipase has 449 amino acid resiudes, and 2 domains, the is smaller with 112 residues, and the consists of 337 residues. Notice that each of these domains consist of 2 identical subunits. Lipase has an a chain and a b chain that each respectively contain 1 of the subunits of the C Terminal Domain and 1 of the subunits of the N terminal domains, all 4 parts come together to form the fully functional enzyme.

The secondary structural elements of Lipase, including the that make up 30 percent of the amino acid chain, and involving 139 residues as well as the that make up 22 percent and 102 residues characterize the structure of the protein.

Important for the tertiary structure of the protein, are several different factors that function to hold each of the domains together in the proper orientation, the certainly make a difference as one might expect, since all proteins generally fold to shield these from interaction with water, the cysteine residues that Lipase has also play a major role since they form , Lipase has 12 disulfide bonds in all.

Lipase Active Sites

The consists of a catalytic triad of residues: Ser 152, Asp 176, and His 263. Residues Phe 77 and Leu 153 are also important for the mechanism of Lipase, functioning as residues to aid in the stabilization of the oxyanion. The catalytic triad is covered by a “lid” that protects the active site of the enyzyme, and prevents the binding of substrate when it is closed and covering the active site, the open lid is stabilized by the formation of hydrogen bonds to neighboring residues. In total lipase has 2 active sites, 1 for each of the domains that make up the enzyme.

Mechanism

The mechanism of action for pancreatic lipase can be broken down into 4 main steps. In the first step His 263 deprotonates Ser 152 that in turn attacks the carboxy carbon of triacylglyceride substrate, it is a nucleophilic addition reaction. In the second step of the reaction the oxyanion hole collapses resulting in the elimination of the diacylglycerol product, that deprotonates His 263 and acylates Ser 152 as a result. In the third step His 263 deprotonates water, which in turn attacks the carboxyl carbon of the acylated Ser 152 in another nucleophilic addition reaction. And in the last step the oxyanion hole collapses again resulting in the elimination of the carboxylate product and Ser 152 which then deprotonates His 263. The reaction of pancreatic lipase is displayed in the following figures.

Reaction 1: Image:M0218.stg01.gif

Reaction 2: Image:M0218.stg02.gif

Reaction 3: Image:M0218.stg03.gif

Reaction 4: Image:M0218.stg04.gif

Ca Ligand

Lipase also has a Ca Ligand that noncovalently binds to residues: Glu 187, Arg 190, Asp 192, Asp 195. There is one Calcium ion bound per chain in the enzyme, so that makes a total of 2 calcium ligands per enzyme. The Ca ligand is an important factor involved in the activation of the enzyme.

Inhibition and Activation

C11 alkyl phosphate is an effective inhibitor of pancreatic lipase, it was synthesized in an attempt to gain a better understanding of the enzyme’s active site. The inhibitor’s alkyl chain fits into the hydrophobic groove of the active site’s catalytic triad and covalently binds to Ser 152, but instead of reacting like the normal triacylglyceride substrate the inhibitor does not react and stays bound, effectively destroying the ability of the enzyme to function.

Bile salts are steroids important for further degradation of the triacylglycerides processed by pancreatic lipase, however they are also inhibitors of the lipase as well. To prevent this inhibition the cofactor colipase is vital. Colipase is secreted by the pancreas in its inactive form procolipase, upon activation the protein binds to the noncatalytic C terminal arm of Lipase to activate the protein.


References


Retrieved from "http://52.214.119.220/wiki/index.php/Sandbox_49"
Personal tools