title: Identification and characterization of a novel L-arabinose isomerase from Anoxybacillus flavithermus useful in D-tagatose production.
abstract: 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.
authors.affiliation: College of Food Engineering and Biotechnology, Tianjin University of Science and Technology, Tianjin, 300457, China.
authors.forename: Yanjun
authors.initials: Y
authors.lastname: Li
authors.forename: Yueming
authors.initials: Y
authors.lastname: Zhu
authors.forename: Anjun
authors.initials: A
authors.lastname: Liu
authors.forename: Yuanxia
authors.initials: Y
authors.lastname: Sun
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D000595:Amino Acid Sequence; D058677:Anoxybacillus / Q000145:classification / Q000201:enzymology* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001881:Borates / Q000737:chemistry; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000302:isolation & purification; D005690:Galactose / Q000378:metabolism*; D019015:Geologic Sediments / Q000382:microbiology; D006601:Hexoses / Q000378:metabolism*; D045482:Hot Springs / Q000382:microbiology; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D021521:Ribotyping; D020539:Sequence Analysis, Protein; D013379:Substrate Specificity; D013549:Sweetening Agents / Q000378:metabolism*; D014871:Water Microbiology
chemical_list: D001426:Bacterial Proteins; D001881:Borates; D004269:DNA, Bacterial; D006601:Hexoses; D012336:RNA, Ribosomal, 16S; D011994:Recombinant Proteins; D013549:Sweetening Agents; D019747:Aldose-Ketose Isomerases; C019715:L-arabinose isomerase; C030192:tagatose; D005690:Galactose