Structural Features of Lipases

The 3D structure of the lipase B from Candida antarctica was first reported by Brady et al. [3], in 1990, and subsequently other lipase structures have been solved [4]. The main features of lipase structures are as follows  

1) An a/p-hydrolase fold consisting of a hydrophobic sheet covered by a-helices on both sides. 

2) An active site located on a P-sheet containing a catalytic triad of serine, histidine and aspartate/glutamate characteristic of all lipases. 

3) An oxyanion hole able to form hydrogen bonds and hence stabilize transition- 

4) An a-hehx lid that covers the active site and ensures that it is not exposed to solvent 

---

The investigation of the unique structural features of lipases has improved our understanding of the mechanism of action of this class of enzymes. In the early 1990s, the first lipase three-dimensional structures were elucidated by X-ray crystallography of the lipases Mucor miehei, Geotrichum candi-dum, and the human pancreatic lipase. Studies revealed a characteristic surface loop (i.e., a lid domain) that covered the active site of the enzyme. 

Persson, B., Bentsson-Olivecrona, G., Enerback, S., Olivecrona, T. and Jorn-vall, H. (1989) Structural features of lipoprotein lipase. Lipase family relationships, binding interactions, non-equivalence of lipase cofactors, vitellogenin similarities and functional subdivision of lipoprotein lipase. Eur. J. Biochem. 179,... 

Inhibition of Lipid Absorption - Agents which decrease the absorption of dietary lipids specifically by inhibiting pancreatic lipase may be suitable for the treatment of obesity. The reduced rate of lipid absorption produced by fenfluramine in rats is probably due to an inhibition of pancreatic lipase. The structural features of a series of phenethylamines, including fenfluramine, required for lipase inhibition have been described using partially purified rat and human pancreatic lipase. Pluronic L-101, a hydrophobic surfactant is a potent inhibitor of pancreatic lipase vitro and reduces body weight gain and carcass lipid after chronic administration to rats. Fecal excretion of dietary lipid is enhanced by Pluronic L-101, thus supporting its action as a lipase inhibitor. 

Mala, J. G. S., and S. Takeuchi. 2008. Understanding Structural Features of Microbial Lipases An Overview. Journal of Analytical Chemistry Insights 3 9—19. 

The book looks deeper into lipases, which are hydrolytic enzymes that have great potential in many industrial applications. The main sources, structure, and features of lipases are presented, with an emphasis on their specificity and interfacial activity. Various industrial applications and property improvements are also discussed. The book focuses on lipase immobilization and its advantages over soluble lipases, where its effects on the physiochemical characteristics, namely, activity and stability, of lipases are discussed. Different immobilization techniques are described, and examples of various immobilization materials are given. In addition, different bioreactor configurations using immobilized lipases are described. 

Mala JGS, Takeuchi S (2008) Understanding structural features of microbial lipases an overview. Anal Chem 3 9-19... 

R. M. Stroud, Structure of Bovine Pancreatic Cholesterol Esterase at 1.6 A Novel Structural Features Involved in Lipase Activation , Biochemistry 1998, 37, 5107-5117. 

Chemoenzymatic polymerizations have the potential to further increase macro-molecular complexity by overcoming these limitations. Their combination with other polymerization techniques can give access to such structures. Depending on the mutual compatibility, multistep reactions as well as cascade reactions have been reported for the synthesis of polymer architectures and will be reviewed in the first part of this article. A unique feature of enzymes is their selectivity, such as regio-, chemo-, and in particular enantioselectivity. This offers oppormnities to synthesize novel chiral polymers and polymer architectures when combined with chemical catalysis. This will be discussed in the second part of this article. Generally, we will focus on the developments of the last 5-8 years. Unless otherwise noted, the term enzyme or lipase in this chapter refers to Candida antarctica Lipase B (CALB) or Novozym 435 (CALB immobilized on macroporous resin). 

Lipases are ester hydrolases acting on triacylglycerols. They achieve their highest catalytic rate at oil-water interfaces. Though they widely differ in size, substrate and catalytic rate and show little sequence similarity, the Ser...His...Asp(Glu) triad in the active site is a structural feature common to serine proteases (cf. Section 3.1.1.) and lipases. Their mechanism of action is not yet fully revealed. X-ray diffraction studies suggest that the putative hydrolytic site is covered by a surface loop and is therefore inaccessible to solvent (Brady et al., 1990 Winkler et al., 1990). Therefore the enzyme... 

The crystal structure of the HGL, expressed in baculovirus/insect ci ll system was obtained at 3 A resolution [35]. This structure was the first to be resolved within the acidic lipases family. HGL is a globular protein that exhibits the a/ hydrolase fold (Fig. 9.2). The final model contains residues 9 to 53 and 57 to 379, six sugar residues located on the four potential N-glycosylation sites and a disulfide bridge Cys 227-Cys 236, whereas Cys 244 is free (Fig. 9.2). In hpases, as weU as in serine proteases [36], the catalytic machinery consists of a triad and an oxyariiori hole. In HGL, the nucleophilic serine (Ser 153) belonging to the usual consensus sequence G-X-S-X-G is located at the cormection between an a hehx and a f strand has an e conformation, which are characteristic features of all enzymes within the alP hydrolase fold family ]21]. His 353 and Asp 324 are the other two residues... 

Again, the use of lipase catalyst for interesterification of edible fats and oils has advantages over the classical chemical catalysts. One of the most attractive features is the unique specificities possible with their use. Nonspecific lipases provide reactions like the random chemical catalyzed interesterification. Specific lipases make it possible to produce fats and oils with a customized triglyceride structure. The enzymatic process can be selective with the use of a positional specificity lipase. These processes are usually much slower and more sensitive to the reaction conditions to provide a better control over the reaction results. Also, the lipases can operate under milder reaction conditions, temperature and pressure, that minimize the formation of side products. 

Zeolite membranes indicate inorganic membranes with a selective/cata-lytic layer composed of a zeolite which is crystalline aluminosilicate with the feature of a high ordered porous structure with size comparable to molecular dimension. An example of the use of zeolites as a catalyst in a multi-phase membrane reactor can be found in Shukla and Kumar (2004) who have immobilized a lipase on a zeolite-clay composite membrane by using glu-taraldehyde as a bifunctional ligand in order to carry out the hydrolysis of olive oil. An application of a zeolite-based membrane in a three-phase membrane reactor has been reported by Wu et al. (1998), where TS-1 zeoUte crystallites were embedded in a polydimethylsiloxane (PDMS) membrane in order to catalyse the oxyfunctionalization of n-hexane (from a gas phase) with hydrogen peroxide (from a liquid phase). 

The most important and typical enzymes that function at lipid-water interfaces in micelles, liposomes, emulsions, etc., are lipases. Lipases are carboxylic ester hydrolases and have been termed glycerol ester hydrolases (EC3.1.1.3) in the international system of classification. They differ greatly as regards both their origins (bacterial, fungal, plant, mammalian, etc.) and their properties, and they can catalyze the synthesis as well as the hydrolysis of a wide range of different carboxylic esters. Numerous reports have appeared about the structure and function of pancreatic lipases, because they are ubiquitous in mammalian species and play important roles in dietary fat absorption [29,30]. In this part, I will describe a structural feature and its relation to catalytic mechanism at the interfaces of lipases, particularly pancreatic lipases. 

Lipases are hydrolytic enzymes that have received extensive attention in food, pulp and paper and fuels industries. They can be found in microorganisms, plants, and animals with ability to breakdown of lipids. In this chapter, lipases are introduced and there is a brief discussion about their functions. This is followed by a short description of their main sources, structure, and features with an emphasis on their specificity and interfacial activity. The chapter focuses on microbial lipases, which are usually preferred for commercial applications due to their favorable properties, easy extraction, and unlimited supply. The chapter concludes with a discussion on the various industrial applications of lipases and properties improvement. 

Aloulou, A., Rodriguez, JA Frederic, C. (2006). Exploring the specific features of interfacial enzymology based on lipase studies. Biochimica et Biophysica Acta(Molecular cell biology og lipids), Vol. 1761,Vol.9, pp. 995-1013 Bockmann, A. C. R. (2006). Structural and dynamic studies of proteins by high-resolution solid-state NMR Chimie, Vol 9, No.3-4, pp 381-392 Auld, D. S. (1997). Zinc Catalysis in Metalloproteases. Structure and Bonding, Vol. 89, pp. 29-50... 

Further information about general properties, structural features, and applications of lipases in organic synthesis is available in a review (Schmid and Verger, 1998), a book chapter (Kazlauskas and Bornscheuer, 1998), and a book (Bomscheuer and Kazlauskas, 1999). 

---