Lipase is a subclass of esterases which catalyzes the hydrolysis of ester bonds in lipid substrates and is essential for fat digestion. It is primarily produced in the pancreas, but can be found in the mouth and stomach as well. The typically digests fat lipids into monoglycerides and free fatty acids, with the resulting monomers subsequently shuttled to the small intestine and eventually absorbed into the lymphatic system. See also Molecular Playground/Pancreatic Lipase.
Introduction
Lipase is a hydrolase that catalyzes the breakdown of lipids by hydrolyzing the esters of fatty acids. Lipases are important in digestion, promoting absorption of fats in the intestines. Lipase is primarily found in the pancreas but is also found in the mouth and the stomach. Pancreatic lipase (PDB ID: 1HPL) which is pictured below is a carboxylic ester hydrolase. It is also commonly called pancreatic triacylglycerol lipase and its enzyme class number is E.C. 3.1.1.3 [1]. The reaction catalyzed by this enzyme is shown below. 
Further breakdown ultimately results in 2-monoacylglycerols and free fatty acids [2]. Pancreatic liapase is a 50 kDa protein, consisting of two identical, 449 residue chains [3]. The determination of the structure and function of lipase was a gradual process. Lipase activity was first demonstrated in the pancreas by Claude Bernard in 1846. It wasn't until 1955 that Mattson and Beck demonstrated a high-specificity of pancreatic lipase for triglyceride primary esters [4]. In recent years, determination of the crystal structure of pancreatic lipase has become the focus and many scientists have worked to further this.
Structure
Hydrophobicity/Hydrophillicity
The is a useful representation of the distribution of hydrophobic and hydrophillic residues. Hydrophobic residues are shown in red and hydrophillic residues in blue. When the hydrophillic residues are removed and only are shown, it is clear that the core of the enzyme is made of hydrophobic residues while the hydrophillic residues are mainly located on the surface of the enzyme.
Lipase Catalytic Mechanism
Although a diverse array of lipase enzymes are found in nature, occupying diverse protein scaffolds, most are built upon an alpha/beta hydrolase fold[5][6] and possess a chymotrypsin-like comprised of an acidic residue, a histidine, and a serine nucleophile. In the case of the images above of a horse pancreatic lipase, the catalytic triad is comprised of [7]
This catalytic triad functions like most found in nature, first with the Aspartic acid forming 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 glycerol backbone of the lipid substrate. A water molecule then donates a proton to the histidine, creating a reactive hydroxyl anion, which can attack the carbonyl carbon of the lipid, releasing the catalytic serine and creating monoglyceride and fatty acid monomers that diffuse away.
Inhibition of Pancreatic Lipase
In this structure, only one of the two identical chains is shown for lipase and colipase to better visualize the interaction of substrates and ligands with the protein. , a C11 alkyl phosphonate, is a competitive inhibitor of pancreatic lipase which binds to the active site. It is highlighted in purple. There are also five B-octylglucoside molecules in association with lipase. They are shown in grey and red. MUP forms hydrogen bonds with : Ser 152 and His 263, which are part of the catalytic triad, and Phe 77 and Leu 153 which are the stabilizing residues located in the oxyanion hole [8].
added by biochem class
Reaction 1:
Image:M0218.stg01.gif
Reaction 2:
Image:M0218.stg02.gif
Reaction 3:
Image:M0218.stg03.gif
Reaction 4:
Image:M0218.stg04.gif
Seen here is the Candida rugosa lipase in
with two molecules of cholesteryl linoleate (grey).
Clinical Significance
Pancreatic lipase is secreted into the duodenum through the duct system of the pancreas. In a healthy individual, it is in 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.[9]
Here, lipase and colipase can be seen
The N-terminal domain also contains a that blocks solvent from entering the active site.
3D Structures of Lipase
Update November 2011
Eukaryote natives:
1hpl – hLip – horse
1hlg – hLip – human - gastric
3jw8, 3hju – mono-glyceride hLip
1jmy – hBSSL
1akn – cBSSL – cattle
2bce - cBSSL (mutant)
1f6w - cBSSL – catalytic domain
3o0d – Lip – Yarrowia lipolytica
1gpl – Lip – Guinea pig
Prokaryote natives:
3guu, 1lbs, 1lbt, 1tca, 1tcb, 1tcc – CaLipA – Candida antarctica
2veo – CaLipA – closed state
3icv – CaLipB (mutant)
1gz7, 1lpm, 1lps– CrLip 2 – Candida rugosa - closed state
1crl, 1trh – CrLip – open state
1llf – Lip – Candida cylindracea
3g7n – Lip - Penicillium expansum
1tia - Lip – Penicillium camemberti
2qua, 2qub – LipA – Serratia marcescens
2hih – Lip – Staphylococcus hyicus
2fx5 – Lip – Pseudomonas mendocina
1yzf – Lip – Enterococcus faecalis
1dt3, 1dt5, 1dte, 1du4, 1ein, 1tib – TlLip - Thermomyces lanuginose
1jfr – Lip – Streptomyces exfoliates
1oil – BcLip - Burkholderia cepacia
2lip – BcLip – open state
1cvl – Lip – Chromobacterium viscosum
1lgy – Lip II – Rhizopus niveus
1tic - Lip – Rhizopus oryzae
1thg – Lip – Geotrichum candidum
3tgl, 4tgl, 1tgl – RmLip– Rhyzomucor miehei
2zvd – PsLip - Pseudomonas sp. – open state
2z8x - PsLip – extracellular
2zj6, 2zj7 – PsLip (mutant)
2z8z – PsLip(mutant) – closed state
3lip, 3a6z - Lip - Pseudomonas cepacia – open state
1qge, 1tah – Lip – Pseudomonas glumae
2w22 – Lip – Geobacillus thermocatenulatus
1ji3, 1ku0 – Lip – Bacillus stearothermophilus
1ah7 - Lip – Bacillus cereus
2qxt, 2qxu, 1isp, 1i6w - BsLip – Bacillus subtilis
3d2a, 3d2b, 3d2c, 1t2n, 1t4m, 3qmm - BsLip (mutant)
2ory – Lip – Photobacterium lypoliticum
2z5g, 2dsn – Lip T1 – Geobacillus zalihae
3p94 – Lip – Parabacteroides distasonis
3ngm – Lip – Gibberella zeae
Lipase/colipase complexes. The colipase is a co-enzyme whose binding to lipase optimizes the enzymatic activity
1n8s – hLip+colipase II
1eth, 1lpa - Lip+colipase II - pig
Hormone-sensitive-lipases (LIPE) hydrolyze the first fatty acid of the triacylglycerol substrate
3k6k – EstE7(LIPE) – metagenome library
3fak, 3dnm – EstE5(LIPE) – metagenome library
1evq – AaEst2(LIPE) – Alicyclobacillus acidocaldarius
1u4n – AaEst2(LIPE) (mutant)
Putative lipases; Proteins with unknown function but structural similarity to lipase obtained in structural genomics projects.
2rau - Lip – Sulfolobus solfataricus
3bxp, 3d3n - Lip – Lactobacillus plantarum
3e0x - Lip – Clostridium acetobutylicum
1z8h – Lip – Nostoc sp. PCC 712
1vj3 - Lip – Nostoc sp.
3bzw – Lip - Bacteroides thetaiotaomicron
2pbl – Lip - Silicibacter
Lipase + inhibitors
3jwe, 3pe6 - mono-glyceride hLip + SAR629 – covalent inhibitor
3l1h – EstE5(LIPE)+FeCl3 – noninvasive inhibitor
3l1i, 3l1j - EstE5(LIPE)+CuSO4 – noninvasive inhibitor
3lij - EstE5(LIPE)+ZnSO4– noninvasive inhibitor
3h18, 3h17 - EstE5 (LIPE)+PMSF
3h19, 3h1b, 3h1a – EstE5 (LIPE)+methyl alcohol
3h1a – EstE5 SLIPE)+ethyl alcohol
3h19 – EstE5 SLIPE)+isopropyl alcohol
3g9t, 3g9u - EstE5 (HSLIPE)+p-nitrophenyl butyrate
3g9z - EstE5 (LIPE) +p-nitrophenyl caprylate
2nw6 – BcLip+ S inhibitor
4lip, 5lip, 1r4z, 1r50 – BcLip+ Rc-(Rp,Sp)-1,2-dioctylcarbamoyl-glycero-3-O-phosphonate
1r4z – BsLip+Rc-IPG-phosphonate
1r50 - BsLip+Sc-IPG-phosphonate
1k8q - Lip+phosphonate – dog
1ex9 – Lip+Rc-(Rp,Sp)-1,2-dioctylcarbamoyl-glycero-3-O-phosphonate – Pseudomonas aeruginosa
5tgl – RmLip+N-hexyl-phosphonate
1lpb – Lip (pig)+colipase+C11 alkyl phosphonate
3icw – CaLipB (mutant) +methyl hydrogen R hexylphosphonate
3a70 – PsLip+diethyl phosphate
Lipase conjugated with analogs to its reaction intermediates
1lpn, 1lpo, 1lpp – CrLip+ sulfonates
3rar – CrLip+ phosphonate
1qz3 – EaEst2(mutant) (LIPE)+hexadecanesulfonate
Lipase showing bile-salt binding site
1aql – cBSSL+taurocholate
Lipase with substrate bound at active site
2zyh – AfLip (mutant)+fatty acid – Archaeoglobus fulgidus
2zyi - AfLip+fatty acid+Ca
2zyr - AfLip+fatty acid+Mg
2zys - AfLip+fatty acid+Cl
1gt6 – TlLip+oleic acid - lipid ligand
Lipase conjugated to transition-state analogs showing the binding mode of the enzyme catalysis
1ys1 – BhLip+hexylphosphonic acid (R) 2-methyl-3-phenylpropyl ester
1ys2 – BhLip+hexylphosphonic acid (S) 2-methyl-3-phenylpropyl ester
1hqd – Lip+1-phenoxy-2-acrtoxy butane – Pseudomonas cepacia
Lipase+lipase chaperone
2es4 – Lip+lipase chaperone C-terminal - Burkholderia glumae
References
- ↑ [1] 1HPL PDB SUM
- ↑ [2] A cross-linked complex between horse pancreatic lipase and colipase
- ↑ [3] 1HPL PDB
- ↑ [4] History of Lipids
- ↑ Sussman JL, Harel M, Frolow F, Oefner C, Goldman A, Toker L, Silman I. Atomic structure of acetylcholinesterase from Torpedo californica: a prototypic acetylcholine-binding protein. Science. 1991 Aug 23;253(5022):872-9. PMID:1678899
- ↑ Ollis DL, Cheah E, Cygler M, Dijkstra B, Frolow F, Franken SM, Harel M, Remington SJ, Silman I, Schrag J, et al.. The alpha/beta hydrolase fold. Protein Eng. 1992 Apr;5(3):197-211. PMID:1409539
- ↑ Bourne Y, Martinez C, Kerfelec B, Lombardo D, Chapus C, Cambillau C. Horse pancreatic lipase. The crystal structure refined at 2.3 A resolution. J Mol Biol. 1994 May 20;238(5):709-32. PMID:8182745 doi:http://dx.doi.org/10.1006/jmbi.1994.1331
- ↑ [5] 1LPB PDB SUM
- ↑ "Pancreatic lipase". Wikipedia: The Free Encyclopedia. 7 Nov 2011 [6]
