Triacylglycerol lipase (pancreatic)

 

Pancreatic lipase from Equus caballus catalyses the conversion of triacylglycerol to 2-monoacylglycerol and free fatty acids. This occurs in the intestine and plays a key role in dietary fat digestion. This is important as it is converting an insoluble substrate into soluble products.

 

Reference Protein and Structure

Sequence
P29183 UniProt (3.1.1.3) IPR002331 (Sequence Homologues) (PDB Homologues)
Biological species
Equus caballus (Horse) Uniprot
PDB
1hpl - HORSE PANCREATIC LIPASE. THE CRYSTAL STRUCTURE AT 2.3 ANGSTROMS RESOLUTION (2.3 Å) PDBe PDBsum 1hpl
Catalytic CATH Domains
3.40.50.1820 CATHdb (see all for 1hpl)
Click To Show Structure

Enzyme Reaction (EC:3.1.1.3)

triglyceride
CHEBI:17855ChEBI
+
water
CHEBI:15377ChEBI
→
hydron
CHEBI:15378ChEBI
+
fatty acid anion
CHEBI:28868ChEBI
+
diacylglycerol
CHEBI:18900ChEBI
Alternative enzyme names: GA 56, GEH, Meito MY 30, PPL, Takedo 1969-4-9, Tween hydrolase, Tweenase, Tweenesterase, Amano AP, Amano B, Amano CE, Amano CES, Amano P, Amno N-AP, Butyrinase, Cacordase, Capalase L, Glycerol ester hydrolase, Glycerol-ester hydrolase, Heparin releasable hepatic lipase, Hepatic lipase, Hepatic monoacylglycerol acyltransferase, Lipase, Lipazin, Liver lipase, Meito Sangyo OF lipase, Post-heparin plasma protamine-resistant lipase, Salt-resistant post-heparin lipase, Steapsin, Triacetinase, Triacylglycerol ester hydrolase, Tributyrase, Tributyrin esterase, Tributyrinase, Triglyceridase, Triglyceride hydrolase, Triglyceride lipase, Triolein hydrolase, Tween-hydrolyzing esterase,

Enzyme Mechanism

Introduction

The negative charge on Asp 176 acts to affect the pKa of His 263, making it more basic. His 263 acts as a general base, by deprotonating Ser 152, activating it for nucleophilic attack on the carbonyl carbon of the ester bond. This forms a negatively charged tetrahedral intermediate which is stabilised by the oxyanion hole formed by the main chain amides of Phe 77 and Leu 153. As the carbonyl is reformed, the ester bond is broken, the leaving group being protonated by His 263. His 263 then acts as a general base again, this time by deprotonating a water molecule, activating it for nucleophilic attack on the substrate carbonyl. Another negatively charged tetrahedral intermediate is formed, and again is stabilised by the oxyanion hole. As the carbonyl is reformed, the substrate-Ser 152 bond is broken, and Ser 152 is then re-protonated by His 263.

Catalytic Residues Roles

UniProt PDB* (1hpl)
Leu166 (main-N) Leu153(154)A (main-N) The main chain amide of Leu 153 acts to stabilise the negatively charged, tetrahedral intermediates. hydrogen bond donor, electrostatic stabiliser
Ser165 Ser152(153)A Part of the Ser-His-Asp catalytic triad. Acts as a nucleophile. covalently attached, hydrogen bond acceptor, hydrogen bond donor, nucleophile, nucleofuge, proton acceptor, proton donor
Asp189 Asp176(177)A The negatively charged Asp 176 helps to activate His 263 to become more basic. activator, hydrogen bond acceptor
His276 His263(264)A Activates Ser 152 by deprotonating it. Donates a proton to the leaving acylglycerol. Activates a water molecule by deprotonating it. Donates a proton back to the leaving group Ser 152. hydrogen bond acceptor, hydrogen bond donor, proton acceptor, proton donor
Phe90 (main-N) Phe77(78)A (main-N) The main chain amide of Phe 77 acts to stabilise the negatively charged, tetrahedral intermediates. hydrogen bond donor, electrostatic stabiliser
*PDB label guide - RESx(y)B(C) - RES: Residue Name; x: Residue ID in PDB file; y: Residue ID in PDB sequence if different from PDB file; B: PDB Chain; C: Biological Assembly Chain if different from PDB. If label is "Not Found" it means this residue is not found in the reference PDB.

Chemical Components

proton transfer, bimolecular nucleophilic addition, overall reactant used, enzyme-substrate complex formation, intermediate formation, unimolecular elimination by the conjugate base, overall product formed, intermediate terminated

References

  1. Lowe ME (1997), J Nutr, 127, 549-557. Molecular mechanisms of rat and human pancreatic triglyceride lipases. PMID:9109604.
  2. Eydoux C et al. (2008), Biochemistry, 47, 9553-9564. Structure of human pancreatic lipase-related protein 2 with the lid in an open conformation. DOI:10.1021/bi8005576. PMID:18702514.
  3. Bourne Y et al. (1994), J Mol Biol, 238, 709-732. Horse Pancreatic Lipase. DOI:10.1006/jmbi.1994.1331. PMID:8182745.
  4. Kazlauskas RJ (1994), Trends Biotechnol, 12, 464-472. Elucidating structure-mechanism relationships in lipases: Prospects for predicting and engineering catalytic properties. DOI:10.1016/0167-7799(94)90022-1. PMID:7765546.
  5. van Tilbeurgh H et al. (1993), Nature, 362, 814-820. Interfacial activation of the lipase–procolipase complex by mixed micelles revealed by X-ray crystallography. DOI:10.1038/362814a0. PMID:8479519.
  6. Winkler FK et al. (1990), Nature, 343, 771-774. Structure of human pancreatic lipase. DOI:10.1038/343771a0. PMID:2106079.

Step 1. His263 (part of a Ser-His-Asp triad) deprotonates Ser152, which attacks the carboxy carbon on the Re face [PMID:7765546] of the triacylglycerol substrate in a nucleophilic addition.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Leu153(154)A (main-N) hydrogen bond donor, electrostatic stabiliser
Ser152(153)A hydrogen bond donor
Phe77(78)A (main-N) hydrogen bond donor, electrostatic stabiliser
His263(264)A hydrogen bond acceptor, hydrogen bond donor
Asp176(177)A activator, hydrogen bond acceptor
Ser152(153)A nucleophile, proton donor
His263(264)A proton acceptor

Chemical Components

proton transfer, ingold: bimolecular nucleophilic addition, overall reactant used, enzyme-substrate complex formation, intermediate formation

Step 2. The oxyanion collapses, initiating an elimination of the diacylglycerol product, which deprotonates His263 and acylated Ser152.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Leu153(154)A (main-N) hydrogen bond donor, electrostatic stabiliser
Ser152(153)A covalently attached
Phe77(78)A (main-N) hydrogen bond donor, electrostatic stabiliser
His263(264)A hydrogen bond donor
Asp176(177)A activator, hydrogen bond acceptor
His263(264)A proton donor

Chemical Components

proton transfer, ingold: unimolecular elimination by the conjugate base, overall product formed, intermediate formation

Step 3. His263 deprotonates water, which attacks the carboxyl carbon of the acylated Ser152 in a nucleophilic addition.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Leu153(154)A (main-N) hydrogen bond donor, electrostatic stabiliser
Ser152(153)A covalently attached
Phe77(78)A (main-N) hydrogen bond donor, electrostatic stabiliser
His263(264)A hydrogen bond acceptor, hydrogen bond donor
Asp176(177)A activator, hydrogen bond acceptor
His263(264)A proton acceptor

Chemical Components

proton transfer, ingold: bimolecular nucleophilic addition, overall reactant used, enzyme-substrate complex formation, intermediate formation

Step 4. The oxyanion collapses, initiating an elimination of the carboxylate product, and Ser152, which deprotonates His263.

Download: Image, Marvin File

Catalytic Residues Roles

Residue Roles
Leu153(154)A (main-N) hydrogen bond donor, electrostatic stabiliser
Ser152(153)A covalently attached, hydrogen bond acceptor
Phe77(78)A (main-N) hydrogen bond donor, electrostatic stabiliser
His263(264)A hydrogen bond donor
Asp176(177)A activator, hydrogen bond acceptor
Ser152(153)A nucleofuge, proton acceptor
His263(264)A proton donor

Chemical Components

proton transfer, ingold: unimolecular elimination by the conjugate base, overall product formed, intermediate terminated
Download: Image, Marvin File

Step 1. His263 (part of a Ser-His-Asp triad) deprotonates Ser152, which attacks the carboxy carbon on the Re face [PMID:7765546] of the triacylglycerol substrate in a nucleophilic addition.

Step 2. The oxyanion collapses, initiating an elimination of the diacylglycerol product, which deprotonates His263 and acylated Ser152.

Step 3. His263 deprotonates water, which attacks the carboxyl carbon of the acylated Ser152 in a nucleophilic addition.

Step 4. The oxyanion collapses, initiating an elimination of the carboxylate product, and Ser152, which deprotonates His263.

Products.

Contributors

Gemma L. Holliday, Ellie Wright, James Willey