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Journal of Bacteriology, September 2001, p. 5050-5057, Vol. 183, No. 17
CREST1 and
Department of Biotechnology, Graduate School of Engineering,
Osaka University, 2-1 Yamadaoka, Osaka
565-0871,2 and Department of Synthetic
Chemistry and Biological Chemistry, Graduate School of Engineering,
Kyoto University, Sakyo-ku, Kyoto 606-8501,3
Japan
Received 11 December 2000/Accepted 4 June 2001
A unique extracellular and thermostable cyclomaltodextrin
glucanotransferase (CGTase) from the hyperthermophilic archaeon Thermococcus sp. strain B1001 produces predominantly
(>85%)
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.17.5050-5057.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Extracellular Synthesis, Specific Recognition, and
Intracellular Degradation of Cyclomaltodextrins by the
Hyperthermophilic Archaeon Thermococcus sp. Strain
B1001

and
-cyclomaltodextrin (
-CD) from starch (Y. Tachibana, et
al., Appl. Environ. Microbiol. 65:1991-1997, 1999). Nucleotide
sequencing of the CGTase gene (cgtA) and its flanking
region was performed, and a cluster of five genes was found, including
a gene homolog encoding a cyclomaltodextrinase (CDase) involved in the
degradation of CDs (cgtB), the gene encoding CGTase
(cgtA), a gene homolog for a CD-binding protein (CBP)
(cgtC), and a putative CBP-dependent ABC transporter
involved in uptake of CDs (cgtDE). The CDase was expressed
in Escherichia coli and purified. The optimum pH and
temperature for CD hydrolysis were 5.5 and 95°C, respectively. The
molecular weight of the recombinant enzyme was estimated to be 79,000. The CDase hydrolyzed
-CD most efficiently among other CDs. Maltose
and pullulan were not utilized as substrates. Linear maltodextrins with
a small glucose unit were very slowly hydrolyzed, and starch was
hydrolyzed more slowly. Analysis by thin-layer chromatography revealed
that glucose and maltose were produced as end products. The purified
recombinant CBP bound to maltose as well as to
-CD. However, the CBP
exhibited higher thermostability in the presence of
-CD. These
results suggested that strain B1001 possesses a unique metabolic
pathway that includes extracellular synthesis, transmembrane uptake,
and intracellular degradation of CDs in starch utilization. Potential advantages of this starch metabolic pathway via CDs are discussed.
*
Corresponding author. Mailing address: Department of
Synthetic Chemistry and Biological Chemistry, Graduate School of
Engineering, Kyoto, University, Sakyo-ku, Kyoto 606-8501, Japan. Phone:
(81) 75-753-5568. Fax: (81) 75-753-4703. E-mail:
imanaka{at}sbchem.kyoto-u.ac.jp.
Present address: Institute of Applied Biochemistry, The University
of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
Present address: School of Materials Science, Japan Advanced
Institute of Science and Technology, Hokuriku, 1-1 Asahidai
Tatsunokuchi, Ishikawa 923-1292, Japan.
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