Lipase

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A computer-generated image of a type of pancreatic lipase (PLRP2) from the guinea pig. PDB 1GPL.

A lipase is a water-soluble enzyme that catalyzes the hydrolysis of ester bonds in water–insoluble, lipid substrates. Most lipases act at a specific position on the glycerol backbone of a lipid substrate (A₁, A₂ or A₃). In the example of human pancreatic lipase (HPL), which is the main enzyme responsible for breaking down fats in the human digestive system, a lipase acts to convert triglyceride substrates found in oils from food to monoglycerides and free fatty acids. Myriad other lipase activities exist in nature, especially when the phospholipases and sphingomyelinases are considered.

Lipases are ubiquitous throughout living organisms, and genes encoding lipases are even present in certain viruses. While a diverse array of genetically distinct lipase enzymes are found in nature, and represent distinct types of protein folds and catalytic mechanisms, most are built on an alpha/beta hydrolase fold (see image) and employ a chymotrypsin-like hydrolysis mechanism involving a serine nucleophile, an acid residue (usually aspartic acid), and a histidine.

Some lipases work within the interior spaces of living cells to degrade lipids. In the example of lysosomal lipase, the enzyme is confined within an organelle called the lysosome. Other lipase enzymes, such as pancreatic lipases, are found in the spaces outside of cells and have roles in the metabolism, absorption and transport of lipids throughout the body. As biological membranes are integral to living cells and are largely composed of phospholipids, lipases play important roles in cell biology. Furthermore, lipases are involved in diverse biological processes ranging from routine metabolism of dietary triglycerides to cell signaling and inflammation. Several different types of lipases are found in the human body, including pancreatic lipase, hepatic lipase, lysosomal lipase, gastric lipase, endothelial lipase, as well as various different phospholipases.

At least three human genetic diseases are caused by mutations in lipase genes. Lipoprotein lipase deficiency is caused by mutations in the gene encoding lipoprotein lipase [1]. Cholesteryl ester storage disease (CESD) and Wolman disease are both caused by mutations in the gene encoding lysosomal lipase, also referred to as lysosomal acid lipase (LAL or LIPA) or acid cholesteryl ester hydrolase [2].

[edit] References

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• Carriere, F., C. Withers-Martinez, H. van Tilbeurgh, A. Roussel, C. Cambillau, and R. Verger. 1998. Structural basis for the substrate selectivity of pancreatic lipases and some related proteins. Biochim Biophys Acta 1376:417-32.
• Diaz, B. L., and J. P. Arm. 2003. Phospholipase A(2). Prostaglandins Leukot Essent Fatty Acids 69:87-97.
• Egmond, M. R., and C. J. van Bemmel. 1997. Impact of Structural Information on Understanding of Lipolytic Function, p. 119-129, Methods Enzymol vol. 284.
• Gilbert B, Rouis M, Griglio S, de Lumley L, Laplaud P. 2001. Lipoprotein lipase (LPL) deficiency: a new patient homozygote for the preponderant mutation Gly188Glu in the human LPL gene and review of reported mutations: 75 % are clustered in exons 5 and 6. Ann Genet 44(1):25-32.
• Girod, A., C. E. Wobus, Z. Zadori, M. Ried, K. Leike, P. Tijssen, J. A. Kleinschmidt, and M. Hallek. 2002. The VP1 capsid protein of adeno-associated virus type 2 is carrying a phospholipase A2 domain required for virus infectivity. J Gen Virol 83:973-8.
• Goni FM, Alonso A. 2002 Sphingomyelinases: enzymology and membrane activity. FEBS Lett. 531(1):38-46.
• Heikinheimo, P., A. Goldman, C. Jeffries, and D. L. Ollis. 1999. Of barn owls and bankers: a lush variety of alpha/beta hydrolases. Structure Fold Des 7:R141-6.
• Lowe, M. E. 1992. The catalytic site residues and interfacial binding of human pancreatic lipase. J Biol Chem 267:17069-73.
• Schrag, J. D., and M. Cygler. 1997. Lipases and alpha/beta hydrolase fold. Methods Enzymol 284:85-107.
• Spiegel, S., D. Foster, and R. Kolesnick. 1996. Signal transduction through lipid second messengers. Curr Opin Cell Biol 8:159-67.
• Svendsen, A. 2000. Lipase protein engineering. Biochim Biophys Acta 1543:223-238.
• Tjoelker, L. W., C. Eberhardt, J. Unger, H. L. Trong, G. A. Zimmerman, T. M. McIntyre, D. M. Stafforini, S. M. Prescott, and P. W. Gray. 1995. Plasma platelet-activating factor acetylhydrolase is a secreted phospholipase A2 with a catalytic triad. J Biol Chem 270:25481-7.
• Winkler, F. K., A. D'Arcy, and W. Hunziker. 1990. Structure of human pancreatic lipase. Nature 343:771-4.
• Withers-Martinez, C., F. Carriere, R. Verger, D. Bourgeois, and C. Cambillau. 1996. A pancreatic lipase with a phospholipase A1 activity: crystal structure of a chimeric pancreatic lipase-related protein 2 from guinea pig. Structure 4:1363-74.

[edit] External links

[edit] Calculated orientations of lipases in membranes

• Lipases from α/β hydrolase superfamily
• Phospholipases A2
• Outer membrane phospholipase A
• Cytosolic phospholipase A2 and patatin
• Bacterial and mammalian phospolipases C
• α-toxin (a bacterial phospholipase C)

[edit] See also

• Phospholipase A
• Phospholipase C
• Alpha toxin
• Peripheral membrane proteins