Roles of Streptococcus mutans dextranase anchored to the cell wall by sortase

Abstract

In order to clarify the role that sortase (SrtA) plays in anchoring dextranase (Dex) to the cell wall of Streptococcus mutans, both Dex- and SrtA- mutants were constructed by insertional inactivation of the respective genes. Western blot analysis with a Dex antiserum showed that in the srtA mutant the Dex was not bound to the cell wall but was secreted into the culture supernatant. In contrast, in the wild type, Dex remained cell-wall-associated. Biological properties of the srtA mutant were examined in dextran fermentation, colony morphology and adherence to a smooth surface. The srtA mutant, as well as the wild type, retained the ability to ferment dextran. However, the colony morphology of the srtA mutant on Todd Hewitt agar containing sucrose was much larger than that of the wild type and showed a ring-like structure. In addition, the srtA mutant was more adhesive to a smooth surface than the wild type when sucrose was present. However, the adhesion of the srtA mutant remarkably decreased by addition of exogenous dextranase. These studies suggest that the SrtA mediates Dex-anchoring to the cell wall in S. mutans, and cell wall-anchored Dex plays a role in controlling both the adhesive properties of extracellular glucan and the ability to utilize extracellular glucan as a nutrient source. In contrast, extracellular Dex is only responsible for degrading extracellular glucan as a nutrient source.

Involvement of Sortase Anchoring of Cell Wall Proteins in Biofilm Formation by Streptococcus mutans

“…Recent studies demonstrated that the S. mutans sortase was involved in the cell wall anchoring of three of them, P1 (11,17), GbpC (13), and DexA (12). These results suggest that S. mutans cells lacking an active sortase may lose the biological function mediated by theses cell surface proteins.…”

Identification and Characterization of a Dextranase Gene of Streptococcus criceti

“…Western blot analysis revealed the cell-wall-associated form (92 kDa) of S. mutans dextranase (11). In S. mutans, a transpeptidase, designated sortase, is responsible for anchoring the dextranase to the cell wall and the cellassociated form of dextranase modulates the adhesive properties of extracellular glucan (11). It has been demonstrated in S. mutans that the release form (96 kDa) of dextranase was proteolytically cleaved into 78 kDa protein by serine protease (15).…”

“…To our knowledge, the cellassociated form of dextranase has not yet been demonstrated in oral streptococci except for S. mutans. Western blot analysis revealed the cell-wall-associated form (92 kDa) of S. mutans dextranase (11). In S. mutans, a transpeptidase, designated sortase, is responsible for anchoring the dextranase to the cell wall and the cellassociated form of dextranase modulates the adhesive properties of extracellular glucan (11).…”

Sortases and the Art of Anchoring Proteins to the Envelopes of Gram-Positive Bacteria

“…Dextranase, on the other hand, is an enzyme that hydrolyzes the ␣-1,6 bonds of certain glucan molecules. This results in the alteration of the solubility and adhesive properties of the glucan substrate and promotes S. mutans biofilm formation (80 (49,158). As may be expected from the lack of anchoring of several adhesins, S. mutans srtA variants displayed a remarkable reduction in their ability to form biofilms (107), in the adhesion to saliva-coated hydroxyapatite in vitro and the colonization of rat teeth in vivo (105), and in the ability to aggregate in the presence of dextrose (82).…”