Kinase activity of the dgk gene product is involved in the virulence of Streptococcus mutans.
C-terminal deletion of the diacylglycerol kinase (Dgk) homologue of the cariogenic oral bacterium Streptococcus mutans resulted in loss of aciduricity. To confirm the role of the C terminus of the Dgk homologue in aciduricity, various mutants of S. mutans UA159 with a C-terminally truncated Dgk homologue were constructed. The deletion of one or two amino acid residues at the C terminus had no effect on the acid-tolerance properties of mutants. When further amino acid residues at the C terminus were removed, mutants became more acid-sensitive. The mutant with deletion of eight amino acid residues at the C terminus did not grow at pH 5.5, suggesting that the C-terminal tail of the Dgk homologue was indispensable for tolerance to acid stress in S. mutans. Kinase activity assays revealed that deletion of the C-terminal amino acids of Dgk led to a reduction of kinase activity for undecaprenol. A truncated mutant that had completely lost kinase activity was unable to grow at pH 5.5. These results suggest that the acid tolerance of S. mutans is closely related to kinase activity of the Dgk homologue. Additionally, the dgk deletion mutant exhibited markedly reduced levels of smooth-surface carious lesions in pathogen-free rats, despite there being no difference between the mutant and the parental organism in the extent of total smooth surface plaque. The results suggest that Dgk activity may play a direct role in the virulence of S. mutans.
Shibata
Yukie
Y
Department of Preventive Dentistry, Kyushu University Faculty of Dental Science, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
van der Ploeg
Jan R
JR
Institute for Oral Biology, University of Zürich, Plattenstrasse 11, CH-8032 Zürich, Switzerland.
Kozuki
Takeshi
T
The Biosignal Research Center, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.
Shirai
Yasuhito
Y
The Biosignal Research Center, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.
Saito
Naoaki
N
The Biosignal Research Center, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan.
Kawada-Matsuo
Miki
M
Department of Preventive Dentistry, Kyushu University Faculty of Dental Science, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Takeshita
Toru
T
Department of Preventive Dentistry, Kyushu University Faculty of Dental Science, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Yamashita
Yoshihisa
Y
Department of Preventive Dentistry, Kyushu University Faculty of Dental Science, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
D000143:Acids / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019852:Diacylglycerol Kinase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D051381:Rats; D017384:Sequence Deletion; D013290:Streptococcal Infections / Q000382:microbiology*; D013295:Streptococcus mutans / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity*; D014774:Virulence
D000143:Acids; D001426:Bacterial Proteins; D019852:Diacylglycerol Kinase