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

Abstract

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 glucanproducing 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.

Biology, immunology, and cariogenicity of Streptococcus mutans.

“…The increased rates of glucan synthesis by lysophosphatidylcholine and primer dextran are additive (248). In a subsequent study, phospholipids normally detected in human oral fluids, e.g., saliva from various glands, gingival crevicular fluids, and serum, enhanced the activity of GTase (503). The GTase level is reported to be increased about fivefold in the presence of 1.0% Tween 80; alteration of the fatty acid composition of the S. mutans cells also occurs (583).…”

Sucrose-promoted accumulation of growing glucosyltransferase variants of Streptococcus gordonii on hydroxyapatite surfaces

“…An alternative explanation is that molecules adsorbed to the surface or sequestered by the attached bacterial populations cause conformational changes in the GTF molecule which favor insoluble glucan production. This has been demonstrated for S. mutans GTF, the conformation of which is altered by high salt concentrations or salivary phospholipids to favor insoluble polymer production (26). It is not known if the GTF activity of S. gordonii is modified in surface-associated populations, although it is known that a 156-kDa form of GTF predominates within the BPM, whereas a 170-kDa form is associated with the unattached cells in the presence of sucrose (30).…”

Incorporation of fatty acids by Streptococcus mutans

“…Salivary lipids potentially influence glucan production by two mechanisms: affecting GTF activity and GTF secretion. More extensive studies, so far focused on the former mechanism, have elucidated a high affinity between GTF and specific lipids which enhance its activity [2,3] and stimulation of glucan synthesis by lysophosphatidylcholine purified from salivary glands [4].…”