Research Progress of the Lipase Modification
Lipase is widely used in the fields of food, chemical industry and biotechnology. The reaction system involves solvent system and water phase system. In order to improve the activity and stability of lipase in the reaction, various methods can be used to modify lipase.
Lipase can catalyze the hydrolysis, alcoholysis, acidolysis, transesterification and esterification of fatty acid esters, and is widely used in food, chemical, pharmaceutical, textile and other fields. Lipase can be applied to water-phase reactions as well as non-aqueous-phase reactions. Lipase is a biocatalyst that is secreted by biological cells and uses protein as the main component. It has the characteristics of good selectivity, high catalytic activity, mild reaction conditions, environmental protection and no pollution. However, natural lipases still have some problems in practical applications, such as the difficulty of separating free enzymes from products, the difficulty of recycling free enzymes, and the poor stability of free enzymes.
In order to solve the problems of natural lipase in practical applications, researchers have used a variety of methods to modify it to improve its function. Enzyme modification technology began in the 1950s and was soon applied to industrial enzyme production. The purpose of enzyme modification is to directionally modify the amino acid residues in the catalytic active center of the enzyme, reveal the composition and catalytic mechanism of the enzyme active center, modify the amino acid side chains that are not related to the composition of the enzyme active center, improve the application performance of the enzyme and the original catalytic function of the enzyme or create new functions. The enzyme interacts with other substances (or compounds) through non-covalent bonds to improve the surface characteristics or application characteristics of the enzyme. According to the different forces between the enzyme and the modified molecule in the modification, the modification methods of the enzyme can be divided into covalent modification and non-covalent modification.
1. Covalent modification of lipase
1.1 Macromolecular modified lipase
Many macromolecules can be activated to modify lipases, such as polyethylene glycol, dextran, dextran, chitin, chitosan and their derivatives. Polyethylene glycol (PEG) is a monofunctional polymer with a series of products with different molecular weights. It has no toxic side effects, no irritation, no immunogenicity, and good water solubility.
In the late 1970s, there have been many reports on the chemical modification of proteins by PEG. Abuchowski's research found that PEG-modified proteins are much more effective as drugs than unmodified proteins. PEG mainly modifies lipase by changing the side chain group of the protein molecule or the main chain structure of the molecule. According to the different PEG modification groups, it can be divided into amino modification, sulfhydryl modification, carboxyl modification and so on. PEG must be activated for chemical modification of lipase, so PEG modification can generally be divided into two steps: First, PEG is activated to connect an active group so that it can bind to certain functional groups of the enzyme protein molecule. Then the activated PEG is covalently bound to the enzyme. At present, the most commonly used activators are: cyanuric chloride (cyanuric chloride), trifluoroethane sulfonyl chloride, chloroformic acid-P-nitrophenyl ester, N-hydroxysuccinimide, etc.
1.2 Small molecule compound modified lipase
Dissociable groups of lipase molecules, such as amino groups, carboxyl groups, hydroxyl groups, sulfhydryl groups, imidazol groups, etc., can all be modified by other active groups. The small molecule modification method uses small molecule compounds such as aldehydes, ketones, carboxylic acids, and fatty acids to react with these free groups such as alkylation, acylation, etherification, etc., to achieve the purpose of modification by changing the nature of the side chain hydroxyl groups.