Role of Streptococcus gordonii Amylase-Binding Protein A in Adhesion to Hydroxyapatite, Starch Metabolism, and Biofilm Formation

Abstract

Interactions between bacteria and salivary components are thought to be important in the establishment and ecology of the oral microflora. ␣-Amylase, the predominant salivary enzyme in humans, binds to Streptococcus gordonii, a primary colonizer of the tooth. Previous studies have implicated this interaction in adhesion of the bacteria to salivary pellicles, catabolism of dietary starches, and biofilm formation. Amylase binding is mediated at least in part by the amylase-binding protein A (AbpA). To study the function of this protein, an erythromycin resistance determinant [erm(AM)] was inserted within the abpA gene of S. gordonii strains Challis and FAS4 by allelic exchange, resulting in abpA mutant strains Challis-E1 and FAS4-E1. Comparison of the wild-type and mutant strains did not reveal any significant differences in colony morphology, biochemical metabolic profiles, growth in complex or defined media, surface hydrophobicity, or coaggregation properties. Scatchard analysis of adhesion isotherms demonstrated that the wild-type strains adhered better to human parotid-saliva-and amylase-coated hydroxyapatite than did the AbpA mutants. In contrast, the mutant strains bound to whole-saliva-coated hydroxyapatite to a greater extent than did the wild-type strains. While the wild-type strains preincubated with purified salivary amylase grew well in defined medium with potato starch as the sole carbohydrate source, the AbpA mutants did not grow under the same conditions even after preincubation with amylase. In addition, the wild-type strain produced large microcolonies in a flow cell biofilm model, while the abpA mutant strains grew much more poorly and produced relatively small microcolonies. Taken together, these results suggest that AbpA of S. gordonii functions as an adhesin to amylase-coated hydroxyapatite, in salivary-amylase-mediated catabolism of dietary starches and in human saliva-supported biofilm formation by S. gordonii.

Amylase-binding proteins A (AbpA) and B (AbpB) differentially affect colonization of rats' teeth by Streptococcus gordonii

“…Salivary amylase retains its enzymic activity while bound to ABS and may facilitate dietary bacterial starch utilization (Douglas, 1990;Rogers et al, 2001;Scannapieco et al, 1990). Amylase binds to high affinity receptors on S. gordonii that cluster around surface cell division sites .…”

“…Amylase binds to high affinity receptors on S. gordonii that cluster around surface cell division sites . Bacterial cells in exponential growth bind more amylase than stationaryphase ones (Rogers et al, 2001;Scannapieco et al, 1992). Amylase-binding components of 20 and 82 kDa are released into culture liquors of S. gordonii strains (Douglas, 1990;Gwynn & Douglas, 1994).…”

Effects of saliva or serum coating on adherence of Streptococcus oralis strains to titanium

“…The major early colonizers of dental biofilms are streptococci, such as Streptococcus oralis, Streptococccus mitis and Streptococcus gordonii, which express adhesins recognizing specific motifs on host proteins (Schachtele et al, 2007;. S. gordonii expresses the SspA/B and Hsa adhesins which recognize sialylated structures on, for example, salivary agglutinin (Jakubovics et al, 2005), as well an amylase-binding protein (AbpA) (Rogers et al, 2001), and has been shown to bind to these proteins in vitro (Murray et al, 1992). However, although S. oralis has been shown to bind to multiple salivary proteins including MUC7, proline-rich proteins and amylase (Murray et al, 1992), the adhesins responsible have not yet been identified.…”

Structure-function relationships in human salivary α-amylase: role of aromatic residues in a secondary binding site

“…Two S. gordonii proteins, AbpA (20 kDa) and AbpB (80 kDa), mediate binding of HSAmy to the bacteria (Douglas et al 1990;Gwynn & Douglas 1994; Rogers et al 1998; Scannapieco et al 1992). The gene encoding the 20 kDa AbpA has been cloned and studied extensively (Rogers et al 1998;Rogers et al 2001) and its role in biofilm formation has been reported (Loo et al 2000). A recent study provided further support for the role of AbpA in human saliva-supported biofilm formation by S. gordonii (Rogers et al 2001).…”

“…The gene encoding the 20 kDa AbpA has been cloned and studied extensively (Rogers et al 1998;Rogers et al 2001) and its role in biofilm formation has been reported (Loo et al 2000). A recent study provided further support for the role of AbpA in human saliva-supported biofilm formation by S. gordonii (Rogers et al 2001). While significant progress has been made in studies regarding bacterial proteins that bind to HSAmy, very little is known about the molecular determinants of HSAmy that are essential for the interaction.…”