Effects of antibodies against a fusion protein consisting of parts of cell surface protein antigen and glucosyltransferase of Streptococcus sobrinus on cell adhesion of mutans streptococci.

BACKGROUND/AIMS: The cell surface protein antigen (PAg) and glucosyltransferases (GTFs) produced by Streptococcus sobrinus are considered to be major colonization factors of the organism. METHODS: We constructed a fusion gene encoding a protein composed of the alanine-rich region of PAg (PAgA) and the glucan-binding domain (GB) of GTF-I, which catalyzes the synthesis of water-insoluble glucan in S. sobrinus. The fusion protein PAgA-GB was purified from cell extracts of Escherichia coli harboring the fusion gene, and antibodies against the fusion protein were prepared in rabbits. RESULTS: In the presence of sucrose, the antibody against PAgA-GB significantly inhibited the adhesion of both S. sobrinus MT8145 and Streptococcus mutans Xc to saliva-coated hydroxyapatite beads, and the inhibitory effect on S. sobrinus was stronger than that on S. mutans. In the absence of sucrose, the antibody against PAgA-GB significantly inhibited the adhesion of both S. sobrinus and S. mutans, however the inhibitory effect on S. sobrinus was unexpectedly weaker than that on S. mutans. A similar result was observed with the antibody against the intact recombinant PAg protein (rPAg), while the same antibody reacted more strongly against S. sobrinus than against S. mutans cells. CONCLUSION: Taken together, these results show that the antibody against S. sobrinus GTF-I may be useful for effective inhibition of the sucrose-dependent adhesion of S. sobrinus. However, PAg of S. sobrinus may not function primarily as a receptor for acquired pellicles, and other cell surface proteins may be involved in the sucrose-independent adhesion of S. sobrinus.

Cysteine biosynthesis in Saccharomyces cerevisiae: a new outlook on pathway and regulation.

Using a Saccharomyces cerevisiae strain having the activities of serine O-acetyl-transferase (SATase), O-acetylserine/O-acetylhomoserine sulphydrylase (OAS/OAH SHLase), cystathionine beta-synthase (beta-CTSase) and cystathionine gamma-lyase (gamma-CTLase), we individually disrupted CYS3(coding for gamma-CTLase) and CYS4 (coding for beta-CTSase). The obtained gene disruptants were cysteine-dependent and incorporated the radioactivity of (35)S-sulphate into homocysteine but not into cysteine or glutathione. We concluded, therefore, that SATase and OAS/OAH SHLase do not constitute a cysteine biosynthetic pathway and that cysteine is synthesized exclusively through the pathway constituted with beta-CTSase and gamma-CTLase; note that OAS/OAH SHLase supplies homocysteine to this pathway by acting as OAH SHLase. From further investigation upon the cys3-disruptant, we obtained results consistent with our earlier suggestion that cysteine and OAS play central roles in the regulation of sulphate assimilation. In addition, we found that sulphate transport activity was not induced at all in the cys4-disruptant, suggesting that CYS4 plays a role in the regulation of sulphate assimilation.

Evaluation of human tooth structure with the ultrasonic imaging technique.

In recent years, ultrasonic waves have been an interesting subject for studies due to their wide range of applications in medical diagnoses. In this study, the acoustic properties of the structure of human teeth was determined with the ultrasonic imaging technique. This study may offer some fundamental findings related to the clinical application of the ultrasonic imaging technique in the further development of a virtual system for dental education and research. Twenty freshly-extracted permanent human teeth (10 molars and 10 premolars) were used to investigate their acoustic velocity and impedance by the ultrasonic image analyzing system with a high-resolution focusing probe. Additionally, the relationship between the acoustic properties and the hardness of the teeth was evaluated. It was found that the acoustic properties of the human teeth were influenced by factors related to their structure, such as degree of calcification, distribution of dentinal tubules, and volume of the dentin matrix. The acoustic velocity and impedance showed an apparent correspondence to the hardness of tooth. This analyzing system provides visual information related to tooth structure that can easily quantitatively evaluate their acoustic properties. It is expected that this system will have a wide range of applications and be further developed for clinical uses.

Regulation of sulphate assimilation in Saccharomyces cerevisiae.

We examined how the activity of O-acetylserine and O-acetylhomoserine sulphydrylase (OAS/OAH) SHLase of Saccharomyces cerevisiae is affected by sulphur source added to the growth medium and genetic background of the strain. In a wild-type strain, the activity was repressed if methionine, cysteine or glutathione was added to the growth medium. However, in a strain deficient of cystathionine gamma-lyase, cysteine and glutathione were repressive, but methionine was not. In strains deficient of serine O-acetyltransferase (SATase), OAS/OAH SHLase activity was low regardless of sulphur source and was further lowered by cysteine and glutathione, but not by methionine. From these observations, we concluded that S-adenosylmethionine should be excluded from being the effector for regulation of OAS/OAH SHLase. Instead, we suspected that S. cerevisiae would have the same regulatory system as Escherichia coli for sulphate assimilation; i.e. cysteine inhibits SATase to lower the cellular concentration of OAS which is required for induction of the sulphate assimilation enzymes including OAS/OAH SHLase. Subsequently, we obtained data supporting this speculation.

Structure of a 2,6-pyridinophane.

2,5,11,14-Tetraoxa-19,20-diazatricyclo-[13.3.1.1(6,10)] icosa-1(19),6,8,10(20),15,17-hexaene, C14H14N2O4, Mr = 274.3, monoclinic, P2(1)/c, a = 9.354(2), b = 9.011(3), c = 7.954(2) A, beta = 101.75(2) degrees, V = 656.4(6) A3, Z = 2, Dx = 1.388 g cm-3, lambda(Mo K alpha) = 0.71073 A, mu = 0.97 cm-1, F(000) = 288, T = 299 K, R = 0.035 for 834 observations with I greater than 3 sigma(I). The molecule lies on an inversion center and is in the anti or stepped conformation. The ethylene glycol chains are fully extended, and the two N-C-O-C torsion angles about the ring-O bonds are near zero, 1.6(2) and -2.3(2) degrees.