Identification and characterization of a novel l-arabinose isomerase from Anoxybacillus flavithermus useful in d-tagatose production

• Published in: Extremophiles : life under extreme conditions Vol. 15; no. 3; pp. 441 - 450
• Main Authors: Li, Yanjun, Zhu, Yueming, Liu, Anjun, Sun, Yuanxia
• Format: Journal Article
• Language: English
• Published: Japan Springer Japan 01.05.2011; Springer; Springer Nature B.V
• Subjects: Aldose-Ketose Isomerases - chemistry; Aldose-Ketose Isomerases - genetics; Aldose-Ketose Isomerases - isolation & purification; Aldose-Ketose Isomerases - metabolism; Amino Acid Sequence; Animal, plant and microbial ecology; Anoxybacillus - classification; Anoxybacillus - enzymology; Anoxybacillus - genetics; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; Bacterial Proteins - isolation & purification; Bacterial Proteins - metabolism; Biochemistry; Biological and medical sciences; Biomedical and Life Sciences; Biotechnology; Borates - chemistry; Cloning, Molecular; DNA, Bacterial - isolation & purification; E coli; Enzymes; Fundamental and applied biological sciences. Psychology; Galactose - metabolism; Genomics; Geologic Sediments - microbiology; Hexoses - metabolism; Hot springs; Hot Springs - microbiology; Hot Temperature; Hydrogen-Ion Concentration; Kinetics; Life Sciences; Microbial Ecology; Microbiology; Molecular Sequence Data; Molecular Weight; Original Paper; Phylogeny; Recombinant Proteins - metabolism; Ribotyping; RNA, Ribosomal, 16S - genetics; Sequence Analysis, Protein; Sludge; Substrate Specificity; Sweetening Agents - metabolism; Water Microbiology; tagatose; arabinose isomerase; Thermophilic; Alkaliphilic enzyme; Anoxybacillus flavithermus; D-tagatose; Intramolecular oxidoreductases; Enzyme; Alkalophily; Thermophily; Identification; L-Arabinose isomerase; Characterization; Isomerases; Extreme environment
• ISSN: 1431-0651; 1433-4909
• DOI: 10.1007/s00792-011-0375-2

d -Tagatose is a highly functional rare ketohexose and many attempts have been made to convert d -galactose into the valuable d -tagatose using l -arabinose isomerase ( l -AI). In this study, a thermophilic strain possessing l -AI gene was isolated from hot spring sludge and identified as Anoxybacillus flavithermus based on its physio-biochemical characterization and phylogenetic analysis of its 16s rRNA gene. Furthermore, the gene encoding l -AI from A. flavithermus (AFAI) was cloned and expressed at a high level in E. coli BL21(DE3). l -AI had a molecular weight of 55,876 Da, an optimum pH of 10.5 and temperature of 95°C. The results showed that the conversion equilibrium shifted to more d -tagatose from d -galactose by raising the reaction temperatures and adding borate. A 60% conversion of d -galactose to d -tagatose was observed at an isomerization temperature of 95°C with borate. The catalytic efficiency ( k cat /K m ) for d -galactose with borate was 9.47 mM −1  min −1 , twice as much as that without borate. Our results indicate that AFAI is a novel hyperthermophilic and alkaliphilic isomerase with a higher catalytic efficiency for d -galactose, suggesting its great potential for producing d -tagatose.