title: Optimizing lactose hydrolysis by computer-guided modification of the catalytic site of a wild-type enzyme.
abstract: Lactose intolerance is a serious global health problem. A lactose hydrolysis enzyme, thermostable β-galactosidase, BgaB (from Geobacillus stearothermophilus) has attracted the attention of industrial biologists because of its potential application in processing lactose-containing products. However, this enzyme experiences galactose product inhibition. Through homology modeling and molecular dynamics (MD) simulation, we have identified the galactose binding sites in the thermostable β-galactosidase BgaB (BgaB). The binding sites are formed from Glu303, Asn310, Trp311, His354, Arg109, Phe341, Try272, Asn147, Glu148, and H354; these residues are all important for enzyme catalysis. A ligand-receptor binding model has been proposed to guide site-directed BgaB mutagenesis experiments. Based upon the model and the MD simulations, we recommend mutating Arg109, Phe341, Trp311, Asn147, Asn310, Try272, and His354 to reduce galactose product inhibition. In vitro site-directed mutagenesis experiments confirmed our predictions. The success rate for mutagenesis was 66.7 %. The best BgaB mutant, F341T, can hydrolyze lactose completely, and is the most promising enzyme for use by the dairy industry. Thus, our study is a successful example of optimizing enzyme catalytic chemical reaction by computer-guided modifying the catalytic site of a wild-type enzyme.
authors.affiliation: State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi 214122, People's Republic of China.
authors.forename: Yi-Ning
authors.initials: YN
authors.lastname: Dong
authors.forename: Ling
authors.initials: L
authors.lastname: Wang
authors.forename: Qiong
authors.initials: Q
authors.lastname: Gu
authors.forename: Haiqin
authors.initials: H
authors.lastname: Chen
authors.forename: Xiaoming
authors.initials: X
authors.lastname: Liu
authors.forename: Yuanda
authors.initials: Y
authors.lastname: Song
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: Arnold T
authors.initials: AT
authors.lastname: Hagler
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang
authors.forename: Jun
authors.initials: J
authors.lastname: Xu
mesh_terms: D020816:Amino Acid Motifs; D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020134:Catalytic Domain; D017076:Computer-Aided Design; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005690:Galactose / Q000737:chemistry* / Q000378:metabolism; D001411:Geobacillus stearothermophilus / Q000737:chemistry* / Q000201:enzymology; D006868:Hydrolysis; D007700:Kinetics; D007785:Lactose / Q000378:metabolism*; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013816:Thermodynamics; D001616:beta-Galactosidase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D011994:Recombinant Proteins; D001616:beta-Galactosidase; D007785:Lactose; D005690:Galactose