Interactions of antisera, sera, and oral fluid with glucosyltransferases

Effects of antibodies to glucosyltransferase on soluble and insolubilized enzymes

OBJECTIVE

Previous studies have shown that glucosyltransferase enzymes (Gtfs) of Streptococcus mutans adsorbed to saliva coated hydroxyapatite (sHA) have distinct properties from the same enzymes in solution. The purpose of the present study was to determine the effects on enzyme activity of polyclonal antibodies raised to Gtfs in a soluble form and bound to sHA.

MATERIALS AND METHODS

Antiserum was raised in six New Zealand White rabbits using the purified glucosyltransferase enzymes (Gtfs) of S. mutans, GtfB, GtfC, or GtfD as soluble antigens or adsorbed to hydroxyapatite (HA, insolubilized). The antisera were examined for their ability to react to these Gtfs and Gtf from Streptococcus sanguis (GtfSs) in Western blot formats as well as inhibit enzyme activity in solution and insolubilized.

RESULTS

Antibodies raised against GtfB or GtfC detected all Gtf enzymes examined in Western blots; antibodies raised to GtfD reacted strongly to GtfD and GtfSs, poorly to GtfC, and was non-reactive with GtfB. Antibodies to GtfB or GtfC inhibited activity of GtfB and GtfC in solution by 90% or more. Enzyme activity adsorbed to sHA was inhibited from 70% to 80% by the same antisera. These same antibodies possessed no specific effect on the activities of either GtfD or GtfSs. Antibodies raised to the GtfD enzyme inhibited activity of GtfD (80% to 90% inhibition) and GtfSs activity (50% to 80%) in solution. In contrast the GtfD antibodies had no effect on the activity of either GtfB or GtfC enzymes in solution. Modest inhibitory effects were noted on GtfC and GtfSs enzymes bound to sHA, but no inhibition was observed for sHA-bound GtfB or GtfD.

CONCLUSION

These data show that some antibodies effective against enzymes in solution may have significantly lesser inhibitory effects against the same enzymes insolubilized. Further, presentation of Gtf antigen immobilized to HA has only a minor influence on the production of antibodies inhibitory to Gtf activity.

Dextran-induced aggregation in a mutant of Streptococcus sobrinus 6715-13

A mutant of wild-type Streptococcus sobrinus 6715-13 has been isolated which resists aggregation by exogenous dextran. This variant is able to form adherent plaque deposits in vitro when cultured in the presence of sucrose and has dextranase activity. In these respects it is the complement of previously described isolates which are plaque formation defective but aggregation normal. Measurements of the incorporation of glucose from glucosyl-labeled sucrose into glucan by cell-associated glucosyltransferase enzyme activity and the thermal labilities of catalytic and receptor functions, as well as the binding of labeled dextrans to the cells, provide evidence that neither dextranase nor glucosyltransferase is the receptor involved in dextran-induced aggregation. Blockage of such bacterial aggregation by anti-glucosyltransferase or anti-dextranase sera suggests cross-reactivity between the antigenic determinants of proteins which recognize alpha(1-6) glucan linkages. A model is proposed, consistent with these and previous findings, in which enzymatic function precedes dextran receptor activity in emergence from the cell. It is also proposed that dextran receptor components of the multireactive glucosyltransferase enzyme(s) and dextranase(s) are spatially separate from, although functionally and antigenically related to, the receptors on the bacterial surface involved in dextran-induced aggregation.

Adsorption of glucosyltransferase to saliva coated hydroxyapatite. Possible mechanism for sucrose dependent bacterial colonization of teeth

Glucosyltransferase (GTF) adsorbed to hydroxyapatite and to saliva coated hydroxyapatite in vitro. Several proteins which are known to be present in the "pellicle" which forms on hydroxyapatite when this mineral is exposed to whole saliva were shown to stimulate or inhibit GTF. It is suggested that these proteins may interact with GTF and cause binding of the enzyme to saliva coated hydroxyapatite. A model is suggested where GTF adsorbed to tooth surfaces may induce binding of microorganisms to tooth surfaces.

Biology, immunology, and cariogenicity of Streptococcus mutans

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Interaction of alpha 2-macroglobulin with L-asparaginase

Obvious protection of the catalytic activity of Esch. coli L-asparaginase by alpha 2-macroglobulin (alpha 2M) was observed under conditions otherwise propitious to the dissociation of the tetrameric molecule into inactive subunits, i.e. very diluted enzyme solutions or the presence of either SDS or urea. The degree of protection depended on enzyme and alpha 2M concentrations respectively, and on the preincubation time of the alpha 2M-enzyme mixture prior to substrate addition. The formation of a catalytically active complex between alpha 2M and L-asparaginase was confirmed by gel filtration on a Sephadex-G column and by polyacrylamide gel electrophoresis. The fact that the migration distance of the active complex corresponded to the migration of alpha 2M and the absence in that case of a migration band corresponding to the intact molecule suggest that complexing of the enzyme with alpha 2M prevented its dissociation into subunits and thus its inactivation. Addition of alpha 2M to the already dissociated enzyme molecule did not restore its catalytic activity. Alpha2-macroglobulin was shown to have an inhibiting effect on the proteolytic activity of almost all proteases and no effect on their esterolytic activity. Furthermore, it prevents the inhibition of esterolytic activity by some natural compounds. The effect of alpha 2M on other types of catalytic activity has not been investigated enough to afford a generalization of the possible role of this macroglobulin in the control of enzyme activity in the body. This paper reports the results of an in vitro study of the effect of alpha 2M on the catalytic activity of an important amidase, i.e. L-asparaginase (L-asparagine amidohydrolase 3.5.1.1), which in recent years has been used in the treatment of acute lymphocytic leukemia in children.

Streptococcus mutans dextransucrase: stimulation by phospholipids from human sera and oral fluids

Serum, gingival crevicular fluid, and parotid, submandibular, and labial minor gland saliva from four individuals stimulated glucan formation from sucrose by the Streptococcus mutans strain 6715 dextransucrase (EC 2.4.1.5). At final dilutions of 1:10 all of the fluids stimulated crude enzyme preparations approximately 1.8-fold. The fluids stimulated the purified water-insoluble glucan-synthesizing form of the dextransucrase approximately 3.2-fold and the water-soluble glucan-producing form of the enzyme approximately 2.4-fold. The fluids all contained concentrations of stimulatory material that could be reduced to undetectable levels only after dilutions of greater than 1:1,000. The increased rates of glucan formation caused by the fluids and dextran were additive, indicating that stimulation by the fluids was primarily due to interactions with entities other than glucan primer molecules. In contrast, the elevated levels of glucan formation in the presence of the fluids was not further enhanced by the addition of lysophosphatidylcholine. Lysophosphatidylcholine purified from parotid and submandibular saliva by solvent extraction and thin-layer chromatography stimulated the dextransucrase as effectively as egg yolk lysophosphatidylcholine. Thus, phospholipids normally found in human oral fluids can enhance the activity of an enzyme believed to be directly associated with the cariogenic potential of S. mutans.

Immunogenic properties of the glucosyltransferase from Streptococcus sanguis OMZ 9: kinetic study of inhibition by antibodies

An anti-glucosyltransferase serum was prepared against a pure enzyme preparation from Streptococcus sanguis OMZ 9, which synthesized both soluble and insoluble dextran. Sera, crude gamma globulins, and antibody fractions obtained after gel filtration on a Bio-Gel P200 column were used to study enzyme-antibody interactions. A strong inhibition of glucosyltransferase activity was obtained only with the purified antibody fraction. Kinetics studies showed that the anti-glucosyltransferase antibodies acted as noncompetitive inhibitors with respect to the substrate (sucrose). The addition of primer dextran in the reaction mixture during preincubation produced a diminution of the inhibition, and the antibodies acted as mixed type inhibitors with respect to dextran. The simultaneous addition of dextran and antibodies can protect the enxyme against antibody inhibition.

Streptococcus mutans dextransucrase: stimulation of glucan formation by phosphoglycerides

Lysophosphatidylcholine (LPC) and other phosphoglycerides stimulated water-insoluble and water-soluble glucan production by the Streptococcus mutans 6715 dextransucrase (EC 2.4.1.5). LPC stimulated crude extracellular dextransucrase 1.7-fold, the water-insoluble glucan-producing alpha form of the enzyme 6.5-fold, the water-soluble glucan-producing beta form of the enzyme 2.1-fold, and the cell-associated dextransucrase 2.0-fold. Kinetic studies demonstrated that LPC did not change the K(m) for sucrose of alpha or beta but increased the maximum velocity of the enzymes. The K(m) for LPC of the alpha enzyme was 10(-5) M. LPC from various sources and synthetic preparations of lauroyl-LPC, myristoyl-LPC, and palmitoyl-LPC all stimulated glucan formation. Portions of phosphoglyceride molecules including fatty acids, phosphatidic acid, glycerophosphoric acid, glycerophos-phorylcholine, and choline, when tested individually or in combinations, did not enhance dextransucrase activity. The increased rates of glucan production caused by LPC and primer dextran were additive. Enzyme incubated with LPC before addition of sucrose was stimulated by dextran primer, and, conversely, enzyme treated with dextran was stimulated by addition of LPC with the sucrose substrate. Thus, dextransucrase can be activated by binding of intact phosphoglyceride molecules to a site on the enzyme that is distinct from either the glucosyl donor or glucosyl acceptor (primer) binding sites. Interactions between the S. mutans dextransucrase and amphipathic phosphoglycerides may explain properties of this enzyme which contribute to the cariogenicity of S. mutans.

Antigens of Streptococcus mutans implicated in virulence--production of antibodies

The present studies assayed antibody activities in serum and saliva of animals immunized by different routes, with cells of S. mutans or cell-free preparations containing GTF, FTF, LTA and/or dextranase synthesized by S. mutans. The results show that the type of immunogenic preparation and the route of its administration can elicit different antibody response and may in part explain the disparity of results achieved by different investigators. The results further emphasize the need to use standardized preparations and carefully described protocols for vaccination.

Antibodies against Streptococcus mutans and glucosyltransferases in caries-free and caries-active military recruits

1) Plaque samples from caries-active recruits showed a higher incidence of S. mutans than plaque samples from caries-free recruits. The persistance of the S. mutans serotypes in the individual plaque samples attested to the consistency of S. mutans in human dental plaque. 2) S. mutans serotype d is predominantly present in approximal plaque of caries-active subjects. 3) Serum antibody titers against S. mutans are higher in caries-active individuals. 4) Sera from caries-free or caries-active individuals inhibit the insoluble glucan synthesis by the cellbound GTF to the same extent. 5) It is unlikely that antibodies against S. mutans in parotid saliva or serum play a major role in the protection against dental caries in Dutch military recruits.

Streptococcus mutans dextransucrase: phosphoglycerides and the detection of inhibitory antibodies in sera

1) Rabbit and human sera contain high concentrations of phospholipids which can interact with dextransucrase causing enhanced glucan production. 2) Antibody in sera capable of blocking glucan synthesis can be accurately detected by adding excess LPC and dextran to the enzyme prior to incubating with antiserum and assaying with sucrose.

Ultrastructural localization of sucrases in Streptococcus mutans GS-5 and an extracellular polysaccharide mutant: a comparative cytochemical and immunocytochemical study

Electron microscopy and cytochemical and immunocytochemical procedures were used to study the ultrastructural distribution of sucrase enzymes in two strains of Streptococcus mutans. In a strongly adherent and virulent parent strain, GS-5, most of the invertase and fructosyltransferase activities were demonstrated extracellularly or bound to the cell surfaces. Intracellularly, enzymatic sites were detected near the plasma membrane on the periphery of the nucleoid and central mesosome. In GS-511, a mutant of diminished virulence and adherence, most of the enzymatic activity was not located on the cell surfaces, but was found away from the cell walls and associated with extracellular polysaccharides. Intracellularly, GS-511 manifested the same distribution of invertase and fructosyltransferase as did GS-5; however, the close association of these enzymes with the plasma membrane was not shown in GS-511. In both strains, extracellular areas near regions associated with cross wall formation appeared to show localized concentrations of these sucrases. Antibodies against partially purified glucosyltransferase (GTF) enzymes from GS-5 were used to localize GTF by immunocytochemical techniques. Indirect ferritin localization procedures showed that the extracellular and cell-bound GTF enzymes were distributed in similar locations as the fructosyltransferase and invertase enzymes. By absorption of the antiserum with whole GS-511 cells, the location of extracellular GTF and surface antigens unique to GS-5 was demonstrated. The dramatically reduced levels of cell-bound sucrase activity in GS-511 indicates the significant role of these enzymes in adherence and cariogenicity.

Antigenic relatedness of glucosyltransferase enzymes from streptococcus mutans

The antigenic relationship of glucosyltransferases (GTF) produced by different serotypes of Streptococcus mutans was studied by using a functional inhibition assay. Rat, rabbit, or hamster immune fluids, directed to cell-associated or supernatant-derived GTF, were tested against ammonium sulfate-precipitated culture supernatants containing GTF from seven strains of S. mutans representing six different serotypes. An antigenic relationship was shown to exist among GTF from serotypes a, d, and g, since both rat and rabbit antisera directed to serotype a or g GTF inhibited GTF of serotypes d and g similarly and both antisera also inhibited serotype a GTF. Furthermore, serum inhibition patterns indicated that GTF of serotypes c and e, and possibly b, are antigenically related to each other, but are antigenically distinct from GTF of serotype a, d, or g. Serum antibody directed to antigens other than enzyme (e.g., serotype-specific antigen or teichoic acid) had little effect on the inhibition assay. Salivas from rats immunized with cell-associated or supernatant-derived GTF exhibited low but consistent inhibition of GTF activity, which generally corresponded to the serum patterns. The sera of two groups of hamsters immunized with GTF (serotype g), enriched either in water-insoluble or water-soluble glucan synthetic activity, gave patterns of inhibition quite similar to those seen with sera from more heterogenous cell-associated or crude supernatant-derived GTF preparations. Both groups of hamster sera also gave virtually identical patterns, suggesting that the two enzyme forms used as antigen share common antigenic determinants. The results from the three animal models suggest that among the cariogenic organisms tested, two (serotypes a, d, g and b, c, e), or perhaps three (serotypes a, d, g; b; and c, e), different subsets of GTF exist that have distinct antigenic determinants within a subset.