Novel substrates of a ribose-5-phosphate isomerase from Clostridium thermocellum.
A substrate specificity study of the recombinant D-ribose-5-phosphate isomerase (RpiB) from Clostridium thermocellum was performed. Among all aldopentoses and aldohexoses, the RpiB enzyme displayed activity with L-talose, D-ribose, D-allose, L-allose, L-ribose, and D-talose in decreasing order. The products released were L-tagatose, D-ribulose, D-psicose, L-psicose, L-ribulose, and D-tagatose, respectively. The enzyme showed specificity for aldose substrates possessing hydroxyl groups oriented in the same direction at the C2, C3, and C4 positions. Molecular modeling of the enzyme suggests that the novel substrate specificity may be explained by substrate interactions with residues Tyr42, His98, and His9, which interact with the hydroxyl groups of C2, C3, and C4, respectively, oriented in the same direction. L-Talose and D-ribulose exhibited the highest activity among the aldoses and ketoses, respectively. Ribose 5-phosphate isomerase catalyzed the conversion of L-talose to L-tagatose with an 89% conversion yield after approximately 90 min, while D-ribulose was converted to D-ribose with a 38% conversion yield.
Yoon
Ran-Young
RY
Department of Bioscience and Biotechnology, 1 Hwayang-dong, Gwangjin-gu, Konkuk University, Seoul 143-701, Republic of Korea.
Yeom
Soo-Jin
SJ
Kim
Hye-Jung
HJ
Oh
Deok-Kun
DK
D019747:Aldose-Ketose Isomerases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D048013:Acetivibrio thermocellus / Q000201:enzymology* / Q000235:genetics; D003198:Computer Simulation; D004926:Escherichia coli / Q000235:genetics; D005947:Glucose / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D007783:Lactones / Q000737:chemistry / Q000378:metabolism; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009005:Monosaccharides / Q000737:chemistry / Q000378:metabolism*; D010429:Pentoses / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012266:Ribose / Q000737:chemistry / Q000378:metabolism; D013237:Stereoisomerism; D013379:Substrate Specificity
D001426:Bacterial Proteins; C510913:L-talo-gamma-lactone; D007783:Lactones; D009005:Monosaccharides; D010429:Pentoses; D011994:Recombinant Proteins; C100182:ribulose; C002055:allose; D012266:Ribose; D019747:Aldose-Ketose Isomerases; C022548:ribosephosphate isomerase; D005947:Glucose