lipase

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.^[1] Lipases thus comprise a subclass of the esterases.

Lipases perform essential roles in the digestion, transport and processing of dietary lipids (e.g. triglycerides, fats, oils) in most, if not all, living organisms. Genes encoding lipases are even present in certain viruses.^[2][3]

Function

Most lipases act at a specific position on the glycerol backbone of lipid substrate (A₁, A₂ or A₃). For example, human pancreatic lipase (HPL),^[4] which is the main enzyme to break down fats in the human digestive system, converts triglyceride substrates found in ingested oils to monoglycerides and free fatty acids.

Several other types of lipase activities exist in nature, such as phospholipases^[5] and sphingomyelinases^[6], however these are usually treated separately from "conventional" lipases.

Structure and Catalytic Mechanism

While a diverse array of genetically distinct lipase enzymes are found in nature, and represent several types of protein folds and catalytic mechanisms, most are built on an alpha/beta hydrolase fold^[7][8][9] (see image^[10]) and employ a chymotrypsin-like hydrolysis mechanism involving a serine nucleophile, an acid residue (usually aspartic acid), and a histidine.^[11][12]

Physiological distribution

Lipases are involved in diverse biological processes ranging from routine metabolism of dietary triglycerides to cell signaling^[13] and inflammation.^[14] Thus, some lipase activities are confined to specific compartments within cells while others work in extracellular spaces.

• In the example of lysosomal lipase, the enzyme is confined within an organelle called the lysosome.

• Other lipase enzymes, such as pancreatic lipases, are secreted into extracellular spaces where they serve to process dietary lipids into more simple forms that can be more easily absorbed and transported throughout the body.

• Fungi and bacteria may secrete lipases to facilitate nutrient absorption from the external medium (or in examples of pathogenic microbes, to promote invasion of a new host).

• Certain wasp and bee venoms contain phospholipases that enhance the "biological payload" of injury and inflammation delivered by a sting.

• As biological membranes are integral to living cells and are largely composed of phospholipids, lipases play important roles in cell biology.

• Malassezia globosa, a fungus that is thought to be the cause of human dandruff, uses lipase to break down sebum into oleic acid and increase skin cell production, causing dandruff. ^[15]

Human lipases

The main lipases of the human digestive system are human pancreatic lipase (HPL) and pancreatic lipase related protein 2 (PLRP2), which are secreted by the pancreas. Humans also have several other related enzymes, including hepatic lipase (HL), endothelial lipase, and lipoprotein lipase. Not all of these lipases function in the gut (see table).

Other lipases include LIPH, LIPI, LIPJ, LIPK, LIPM, LIPN, MGLL, DAGLA, DAGLB, and CEL.

There also are a diverse array of phospholipases, but these are not always classified with the other lipases.

Industrial uses

Lipases from fungi and bacteria serve important roles in human practices as ancient as yogurt and cheese fermentation. However, lipases are also being exploited as cheap and versatile catalysts to degrade lipids in more modern applications. For instance, a biotechnology company has brought recombinant lipase enzymes to market for use in applications such as baking, laundry detergents and even as biocatalysts^[22] in alternative energy strategies to convert vegetable oil into fuel.^[23][24]

Additional images

General formula of a carboxylate ester

Glycerol

General structure of a triglyceride

See also

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

References

External links

• MeSH Lipase
• Selective Inhibitors of Monoacylglycerol Lipase as a Treatment for Neurological Disorders 2004-637
• UMich Orientation of Proteins in Membranes families/superfamily-90 - Phospholipases A2
• UMich Orientation of Proteins in Membranes families/superfamily-29 - Outer membrane phospholipase A
• UMich Orientation of Proteins in Membranes families/superfamily-134 - Cytosolic phospholipase A2 and patatin
• UMich Orientation of Proteins in Membranes families/superfamily-126 - Bacterial and mammalian phospolipases C
• UMich Orientation of Proteins in Membranes families/superfamily-88 - α-toxin (a bacterial phospholipase C)