title: Molecular characterization of cold-inducible beta-galactosidase from Arthrobacter sp. ON14 isolated from Antarctica.
abstract: A psychrotrophic bacterium, Arthrobacter sp. ON14, isolated from Antarctica, was shown to exhibit a high beta-galactosidase activity at a low temperature. A genomic library of ON14 was constructed and screened for beta-galactosidase genes on functional plates containing 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal) as the substrate. Two different beta-galactosidase genes, named as galA, galB, were found in ON14. Computational analyses of the genes revealed that the encoded protein GalA belongs to family 2 of glycosyl hydrolysases and is a cold-active protein, whereas GalB belongs to family 42 of glycosyl hydrolysases and is a mesophilic protein. Reverse transcription analyses revealed that the expression of galA is highly induced at a low temperature (4 degrees C) and repressed at a high temperature (28degreesC) when lactose is used as the sole carbon source. Conversely, the expression of galB is inhibited at a low temperature and induced at a high temperature. The purified GalA showed its peak activity at 15 degrees C and pH 8. The mineral ions Na+, K+, Mg2+, and Mn2+ were identified as enzyme activators, whereas Ca2+ had no influence on the enzyme activity. An enzyme stability assay revealed that the activity of GalA is significantly decreased when it is incubated at 45 degrees C for 2 h, and all its activity is lost when it is incubated at 50 degrees C.
authors.affiliation: School of Life Science, Xiamen University,Xiamen, P R China.
authors.forename: Ke
authors.initials: K
authors.lastname: Xu
authors.forename: Xixiang
authors.initials: X
authors.lastname: Tang
authors.forename: Yingbao
authors.initials: Y
authors.lastname: Gai
authors.forename: Muhammad
authors.initials: M
authors.lastname: Mehmood
authors.forename: Xiang
authors.initials: X
authors.lastname: Xiao
authors.forename: Fengping
authors.initials: F
authors.lastname: Wang
mesh_terms: D000595:Amino Acid Sequence; D000864:Antarctic Regions; D001173:Arthrobacter / Q000201:enzymology* / Q000302:isolation & purification; D002412:Cations / Q000378:metabolism; D003067:Coenzymes / Q000378:metabolism; D003080:Cold Temperature; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004795:Enzyme Stability; D005697:Galactosides / Q000378:metabolism; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D015723:Gene Library; D007211:Indoles / Q000378:metabolism; D007785:Lactose / Q000378:metabolism; D008670:Metals / Q000378:metabolism; D008969:Molecular Sequence Data; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D001616:beta-Galactosidase / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D002412:Cations; D003067:Coenzymes; D004269:DNA, Bacterial; D005697:Galactosides; D007211:Indoles; D008670:Metals; D001616:beta-Galactosidase; D007785:Lactose; C044888:5-bromo-4-chloro-3-indolyl beta-galactoside