Analysis of a dextran-binding domain of the dextranase of Streptococcus mutans.
OBJECTIVE
To examine the dextran-binding domain of the dextranase (Dex) of Streptococcus mutans.


RESULTS
Deletion mutants of the Dex gene of Strep. mutans were prepared by polymerase chain reaction and expressed in Escherichia coli cells. Binding of the truncated Dexs to dextran was measured with a Sephadex G-150 gel. Although the Dexs which lacked the N-terminal variable region lost enzyme activity, they still retained dextran-binding ability. In addition, further deletion into the conserved region from the N-terminal did not influence the dextran-binding ability. However, the Dex which carried a deletion in the C-terminus still possessed both enzyme activity and dextran-binding ability. Further deletion into the conserved region from the C-terminal resulted in complete disappearance of both enzyme and dextran-binding activities.


CONCLUSIONS
Deletion analysis of the Dex gene of Strep. mutans showed that the C-terminal side (about 120 amino acid residues) of the conserved region of the Dex was essential for dextran-binding ability.


CONCLUSIONS
The dextran-binding domain was present in a different area from the catalytic site in the conserved region of the Dex molecule. The amino acid sequence of the dextran-binding domain of the Dex differed from those of glucan-binding regions of other glucan-binding proteins reported.
Department of Oral Microbiology, Showa University School of Dentistry, Shinagawa-ku, Tokyo, Japan. morisaka@dent.showa-u.ac.jp
H
H
Morisaki
T
T
Igarashi
A
A
Yamamoto
N
N
Goto
D000595:Amino Acid Sequence; D017124:Conserved Sequence; D003910:Dextranase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D003911:Dextrans / Q000378:metabolism*; D017353:Gene Deletion; D005936:Glucans / Q000378:metabolism; D008969:Molecular Sequence Data; D013295:Streptococcus mutans / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics*
D003911:Dextrans; D005936:Glucans; D003910:Dextranase